Month: October 2021

#0034: Repair and analysis of a tap cartridge

Otto

#0034: Repair and analysis of a tap cartridge

Preamble

I recently had to repair a constantly dripping kitchen faucet, and thought that I may as well document it. Especially since I found the construction of the cartridges within the tap to be rather interesting. Although I must say that the title does make me feel a bit silly.

Tools and Materials used

Tools:

  • crescent wrench / 17mm wrench
  • nylon spudger / pry tool
  • phillips screwdriver
  • soft bristle toothbrush
  • plastic container
  • pipette
  • teaspoon

Materials:

  • petroleum jelly / plumber’s grease
  • vinegar
  • water

Tap cartridge inspection

I’d like to start by examining the water faucet’s cartridges themselves, as this information will be relevant later during the repair. The two pictured cartridges were taken from a quarter turn kitchen tap. This is a tap that only requires the handle to be turned 90 degrees around it’s axis, in order for it to go from a fully shut to a fully open state, and vice versa.

This type of cartridge is designed so that water flows into it from the central hole at it’s bottom inlet. This water then flows up inside it’s shaft, and through the two holes within the first ceramic disc. It is then diverted out through the two radial holes on it’s side via the second ceramic disc. At which point the water has a direct route to the faucet head.

This particular type of cartridge has two ceramic/plastic discs within it, that in conjunction with each other operate as a single water control valve. They do this by establishing a water tight seal between them; a press fit seal that is created by the two discs merely pressing against each other in a way that eliminates any gaps between them.

This seal is demonstrated within the video below, where you can see a suction effect take place between the two discs. This suction helps the two discs adhere to each other when wet. This is only possible due to the absolutely smooth surface of the first disc, coupled with the hollow cups present on the second disc’s contacting surface.

These two ceramic valve discs are both keyed to fit into their brass metal shaft in one particular orientation. This orientation has the bottom disc operate as a fixed or stationary valve. Whose job it is to split the ingressing water into two separate streams. It does this via the two distinct triangular quarter-circle holes within it. This lower disc is keyed to fit into the inner wall of the cartridge’s cylindrical housing in a way that makes it immovable.

Whereas the top disc is keyed into the rotating tap handle cylinder attachment. This allows the tap handle to control the rotation of the upper disc. This upper disc is cut in a way that either blocks the two water channels provided by the bottom disc when closed; or when open: diverts water from the holes of the bottom disc outwards to the radial holes in the cartridge housing. This water is then further diverted up and out of the tap for use.

The reason why it only takes a quarter turn to fully open the water channels of this type of cartridge: is due to the placement of holes and channels within these ceramic discs. The first (bottom) disc has two oppositely placed holes within it. Each taking up approximately a quarter section of the circular valve.

This quartering is then reflected within the top ceramic disc. Which consists of two opposing cupped flat plates, and two opposing angled wedges: which veer off to the radial holes within the brass cartridge housing. And since these channels take up opposing quarters of their discs – it only takes a quarter turn to either align both holes of the bottom plate with the upper disc’s water outlet ramps, which then allows water to pass; or with the flat plates, which then blocks the water at both holes.

Cartridge operation demo video

Valve operation demo video

Suction effect demo video

Dripping fault Analysis

Dripping fault cause theory

The fault that causes a dripping tap can be due to a number of different factors. Probably the most straight forward scenario includes water simply making it’s way around the rubber o-rings and/or water gasket. This could happen if the rubbers have gotten old or heat damaged, and started contracting or cracking as a result. Alternatively, they could’ve been disturbed or are otherwise not seated correctly in order to form an effective water barrier.

This means that whatever water does manage to get around these seals can then bypass the cartridge altogether and shortcut it’s way to the faucet head. The severity of the leak in this case would be directly proportionate to the ineffectiveness of the rubbers to seal out water.

Another issue could be within the cartridge itself. With water entering the cartridge and then passing through the cartridge valve by squeezing between the two ceramic disc plates due to an imperfect seal. This pressure fit seal between the two disc plates could be undermined by a number of different factors.

The most likely of which are a build up of limescale on the the ceramic discs themselves. Limescale is a broad term to encompass residual build up of the carbonates present in drinking water; such as calcium and magnesium carbonate. Water rich in minerals like this is often referred to as “hard water”.

Limescale build up on the contact surfaces between the ceramic discs, can cause them to then become uneven as the limescale adheres to them. Specifically the drip issue is caused because the valleys in this now uneven surface provide the water a small pathway across the pressure seal’s threshold when it is closed.

Another issue that could cause the valve to no longer function effectively is scoring of the inter-disc surface. Essentially scratches that then allow some water to pass through their valleys when the valve is closed. A likely cause of this could be something as basic as wear and tear. The two discs grinding each other down over an extended period period of time due to standard use. This happening with just the minor friction created from repeated opening and closing over time, eventually compromising the watertight seal as disc surface material is lost.

Before moving on, I should mention that this section is largely speculation. Basically educated guesses based on my observations during the disassembly. That being said these theories above are the one’s that I went into this repair with.

Dripping fault effect

A continuous drip may initially seem like a minor fault, because it is. However, this fault incurs a waste of resources. A slow but continuous one, that is hard to easily assess. Simply put it wastes water, and probably more than you might expect as well. Just because it only wastes a drop at a time, it doesn’t mean that it isn’t wasting a lot cumulatively. It just makes it difficult to easily see the totality of wastage.

Sampling methodology

Let’s try to get a rough idea of how much water is lost due to this fault. Note that this is not going to be very scientific. It is just a test to get a rough idea of water wastage. With that in mind, there are two discrete pieces of information that are required: 1) is the average water droplet volume; and 2) the number of water drips within a set period of time. In this case the sample time will be 1 minute.

I captured a single drop using a teaspoon. Then sampled it using a random plastic pipette that I had on hand. I repeated this a few times and found the droplets to be rather consistent in volume. Unfortunately, due to the pipette’s lack of precision, I was forced to visually estimate this volume between it’s labelled increments.

Collected observations

  • This leaky tap consistently provided around 13 drips within any one minute period.
  • With each drop having a volume of approximately 0.3 ml each.

Water drip rate and predictive volume lost

  • 1 minute: 13 drips @ 3.9 ml
  • 1 hour: 780 drips @ 234 ml
  • 1 day: 18720 drips @ 5616 ml (~5.6 litres)
  • 1 week: 131040 drips @ 39312 ml (~39 litres)
  • 1 month: 524160 drips @ 157248 ml (~157 litres)

Leaking faucet demo videos

Droplet sampling demo video

Leak conclusion

Interesting result. If a household either has a limited water supply (e.g. off-grid), or is on a metered supply where they pay for water by volume; then 157 litres lost in wastage in a single month by a single tap is not insignificant.

I hope this has illustrated how important it is to fix even minor faults such as this as soon as possible. 157 litres of water used could very well cost a metered household more money on the fault’s first month on the household’s monthly water consumption bill, than a complete cartridge replacement for that tap otherwise would have.

Repair process

Getting at the parts

First thing first. Common sense. I switched off the water by closing the main water valve for the house. This was located under the kitchen sink for me. This is an essential step in the same way as one would switch off the electricity before working on an electrical outlet, one needs to turn off the water before working on a water outlet. You’d think that was common sense right? But I have seen too many plumber fail videos online that say otherwise.

After giving the kitchen faucet a once over, and looking online I decided that the tap cartridges are the most likely suspects for the drip, so I set upon getting at them. Since I have never taken a kitchen sink tap apart before, I engaged in what I call an exploratory disassembly. Prodding and poking the device looking for hidden clips and screws.

To cut to the point: I used a nylon spudger to pry open the (metal coloured) plastic screw cover on each tap. I recommend using a plastic pry tool to avoid scratching the finish off of any part of the tap. Next. I unscrewed the phillips metal screws which attached each tap handle to the rotatable cartridge cylinder section below them. After setting aside the tap handles, I then removed the full cartridge assembly from the faucet housing using a wrench. As for disassembling the cartridges themselves, they come apart toolessly in-hand. That’s it. Easy.

Inspection

Like every repair, this one begun with a thorough inspection. A basic visual inspection did not reveal anything obviously wrong with either cartridge to my eyes. However once I disassembled both hot and cold units, I noticed that the internal plastic disc valves on the cold water side felt rough to the touch. Likely indicating a build up of limescale. Most notably this was even apparent on the surfaces between the two valves. And since these two surfaces come together to form the press fit seal that controls water flow: I concluded that this was likely the specific cause to this particular leak.

Limescale build up is nothing unusual for my particular location, as I do live in a heavy water area. However the odd part was that all the limescale build up was on the cold water side cartridge of our kitchen tap. With little to none on the hot water cartridge. This is really unusual in my opinion because I believe that higher temperatures should exacerbate limescale build up. The average water kettle should be a testament to this theory. However in this case the limescale build up was only sufficiently present on the cold water side.

A working theory I have concerns the on demand water heater which directly supplies this tap – a boiler which my household recently (1.5 years) had professionally installed. I believe that it has some-kind of water filter (or softener, or descaler…) that has been fitted to minimize limescale build up within the unit as it heats water. This means that the hot water provided by it to the tap would have less mineral contaminants (i.e. be softer) than the cold side. I would verify this, but it is not a pressing issue and not worth digging the unit out at this moment to confirm.

Cleaning the cartridge

Once I decided that it was limescale that was undermining the valves press-fit seal, I decided to take the already disassembled cartridges and submerged them into a vinegar solution. The idea is that the mild acid of vinegar will react with the alkaline limescale and dissolve it into the liquid solution.

After about an hour, I removed the parts and brushed them all down with a basic toothbrush in order to remove any loosened remaining debris. I did however take care not to scratch or score the plastic valves as any scoring would also undermine their ability to form a watertight seal; as this would allow water would pass through the miniscule divots that would be present on the seal’s contacting surfaces.

With regards to this method, I should note that I made exceptions for the rubber parts of the cartridges. The blue o-rings and red/blue rubber gasket. I just did not feel comfortable submerging them in an acidic solution for extended periods. I feared that it may affect the chemistry of the rubber material and ‘dry’ it out. Thus causing it to crack or split; and consequently be no longer effective as a waterproof seal. (FYI the pictures below are lying.)

Testing

After a quick rinse in tap water I decided to reassemble the cartridges and put them back into service for extended testing. Although the leaking was significantly reduced as it didn’t drip continuously as before: it still dripped regularly. This was tested by leaving an empty cup under the tap head overnight. I’d regularly find the typical coffee cup I used at least half-full come morning.

This lead me to surmise a number of scenarios:

1) That the water was making it in between the the plastic valve seals. Likely due to surface scoring caused by either my cleaning/brushing of the valve discs; or the limescale itself being ground into the discs as they operated over the years.

2) Water is making it’s way around the gaskets and o-rings, in addition to bypassing the valves. And that I have only remedied/alleviated one issue.

Greasing the cartridge components

With these conclusions I decided to then purchase some plumber’s grease. Thinking that it would be perfect for the application of assisting the plastic disc valves and rubber gaskets to form water tight seals. The Ebay listing for it explicitly stated just that.

However once the product arrived, I decided that I wouldn’t be testing it’s efficacy as I decided that it was not fit for use. The reason why: was that the little tin came with a whole host of warnings on it’s label. Warnings typically associated with poisonous chemical products.

Particularly the “Do not eat, drink, or smoke …” around this product warning gave me pause. Especially when coupled with the fact that the very vapours from this thing were an irritant. It emitted a vapour that was a mild irritant to the eyes and nose, smelling almost minty like the ointment “tiger balm”.

So despite the labelling assuring me that it is indeed appropriate for use within water faucets, I decided that this was not something that I wanted coming in contact with my drinking water – and ultimately ending up inside me. Maybe I am just paranoid. Maybe not.

Either way if an irritant chemical has warnings not to ingest it, and by using it for it’s intended purpose you are essentially guaranteeing ingestion. Maybe don’t use that chemical. Ultimately, it all just comes down to personal choice, and how much you trust anonymous Ebay sellers over your own intuition.

Personally I just found a substitute: Petroleum Jelly. A non irritant, non toxic chemical that routinely comes in contact with human skin and lips. So chances are good that it won’t do any harm if you accidentally ingest some with your drinking water.

Additionally unlike the plumber’s grease, the jelly can be used with rubbers like the o-rings and gaskets. I used to use some back in school within the science lab. A small amount was applied to the mouth of a bunsen burner’s rubber gas hose in order to help form a gas-tight seal between it and it’s brass attachment. I remember it even hydrating the dry red rubber of those hoses. Although I am pretty sure that petroleum jelly is also flammable so I’m not sure if that was a particularly safe application for it. :/

However within this application: my only concern with petroleum jelly is it’s longevity in the system, and heat resistance. However those are considerably less concerning than putting poison in a drinking tap. So after greasing everything up: the o-rings, the rubber gasket, and the plastic valve discs, then tighten everything down properly – I did note further improvement. Now the faucet barely leaks at all. Barely being the keyword here.

Jobs a gudd’un mate.

Post repair review

I left some time after the repair for observation before writing this review and it seems the leak is slowly returning after a month. A month of constant use keep in mind. I am still chalking it up as a success because this repair really only needed some basic tools and materials. The only consumables used are just household sundries like vinegar and pure petroleum jelly. So it can be done for next to nothing.

There are even more things I could do short of purchasing replacement cartridges, and that would be to use an additional o-ring under the main water ingress rubber gasket. This will put more pressure on the plastic disc valves. Squashing them together to form an even tighter pressure fit seal between them.

Although there are likely drawbacks to this, including and not limited to: firstly, a stiffer tap – the more downward pressure on the cartridge mechanism, the harder it would be to rotate it; and secondly, the higher pressure on the discs themselves would cause them to grind against each other more, and likely shorten their lifespan by promoting scraping of their contact surfaces.

Although if you are repairing it in the first place, chances are that they are already well towards their end-of-life, in which case this fix will extend it couple of months before they likely fail into a unrepairable state. At which point replacing the ceramic discs will be needed. Just my guess.

Closing thoughts

Not much to say here really, I surmised my thoughts on the repair itself within the Post repair review above. So I’ll go with a more personal note here.

I actually enjoyed looking at this tap cartridge more than I thought I would. It really is amazing what people are capable of creating through iterative design and mass production. It reminds me of the gaming concept of min-maxing: of getting the most out of the lest.

I mean look at the simple design and construction of this cartridge. It uses two plastic/ceramic discs to create a watertight seal by just pressing against each other. Undoubtedly the results of iterative cost cutting to the point of being adequate or acceptable, and little more.

I know that when I usually talk about cost cutting, especially when discussing mass produced goods: its usually in a negative light. That’s because the stimuli or catalyst for those tangential rants tends to be a product that is sub par, and in my opinion not fit for purpose. Products that I refer to as “factory fresh e-waste”.

However that is not the case here, these cartridges are fit for purpose. But they are also (in my humble opinion) built down to a price point. One that makes economical sense. Look at the bill of materials here for example: a brass housing and insert, a retaining clip for the insert, a metal washer, two o-rings, a water gasket, a metal screw, two plastic/ceramic discs, and maybe one or two additional miniscule hidden parts that I missed. That is a list that has been reduced to the absolute necessities and little more, but nothing less either. I admire the philosophy honestly.

Anyway, enough gushing about the tap. Since I repaired it: it’ll do that itself in a year or two ;). Upon looking up the Ebay prices for replacements, I noticed that they are very cheap. (At least the generic versions.) The average price for a set of two is £10; and if you wanted to repair your own two cartridges with a kit of replacement o-rings, gaskets, and ceramic discs, then that’ll set you back around £2.50. Very doable.

As a final note, if you found yourself confused as to why I kept referring to the cartridge discs as both made out of plastic and ceramic. Well, this is because the unit I was working on (pictured) felt like plastic to me. A hard somewhat brittle plastic.

However upon looking them up online, apparently they are all ceramic. I also wrote the repair section during the repair process prior to this; and I decided to leave it as plastic because that’s what I felt that material was while I was handling it. Although I am by no means an expert on such things, if the internet says that it’s ceramic then I guess it likely is.

Thank you for reading.

Links, references, and further reading

https://en.wikipedia.org/wiki/Hard_water

#0033: Repair and modification of a Stylophone

Otto

#0033: Repair and modification of a Stylophone

Preamble

As a bid to get myself into creating music – or at the very least something music adjacent: I decided to purchase a Stylophone. A simple and cheap electronic synthesiser. Something budget friendly and fun looking with which to test out the waters.

What is a Stylophone and how does it function?

If you are unfamiliar with what a Stylophone is, I will briefly explain. A Stylophone is a handheld electronic musical instrument. A synthesiser that creates audible waveforms from electricity.

The most notable feature of this instrument is it’s set of oversized PCB (Printed Circuit Board) pads, which operate as musical keys. These keys are accompanied by an electrically wired stylus, which functions as their activator. To play a note, one just has to touch the stylus to a keypad. This then closes an electrical circuit within the device, in essence mimicking a keyboard (button) press.

Broadly speaking, component-wise: at the heart of a typical Stylophone lies a voltage controlled oscillator. This component creates a waveform when fed a DC voltage. This waveform is then fed to the speaker to create an audible tone. Since this is a voltage controlled oscillator, it means that it’s output waveform is dependant on the input voltage supplied. Thus voltage is used to control the specific sounds produced.

To control the oscillator input voltage, each musical note key on a Stylophone has it’s own circuit with it’s own unique resistor values that are different from all the other note keys. These resistors are used with the intention of stepping down the 9 volts input into whatever each note-key’s desired oscillator supply voltage is.

Although there is undoubtedly more to discuss on Stylophones; such as how the pitch change, or vibrato functions operate: they are largely out-of-scope for this simple introduction. Although I will go into further detail if/when I do a full device analysis on this Stylophone. (Link below when/if that article is written.) However in general Stylophones like this one are really not too complicated devices.

Tools and equipment

Tools:

  • soldering iron
  • hot glue gun
  • toothbrush
  • tweezers
  • desoldering pump

Consumables:

  • hot glue
  • isopropyl alcohol
  • desoldering braid
  • (leaded) solder
  • solder flux

Components:

  • red 5mm⌀ through-hole LED
  • ethernet wire (multi-strand copper wire)
  • 10kΩ potentiometer
  • toggle switch

Device Repair

Fortunately (or perhaps unfortunately for this article) the device needed very little fixing. It’s main faults were either cosmetic in nature or trivial to fix; and since the Stylophone was basically fully functional, other than the dirt and grime that had gotten into it over the years: there’ll consequently be little to say about it in this regard.

I will say that the sound it produced was a bit choppy (intermittent), probably due to dirty contacts on the keypad. This issue of dirty contacts applied to the two built in slide switches as well, as they where notably unresponsive. Flicking them produced unreliable results.

More specifically: flicking the power switch on didn’t always cause the device to power on. I had to toggle it a couple of times for it to operate as expected. Additionally I couldn’t even tell at the time that the “Vibrato” button wasn’t functioning. It was only until after it was cleaned and started working, that I realised what it actually did. It makes the sound of the notes “wobble”.

Since these slide switches were built into the PCB itself, rather than a discrete component than can be easily removed: I decided that the best course of action was to simply inject some isopropyl alcohol into them. Then work the switches on and off until they self cleaned. The combination of the alcohol breaking down the embedded grime chemically, and the friction from mechanical manipulation cleaned the electrical contacts.

Moving on. I cleaned the PCB keypad in a similar way. Dousing it in alcohol and scrubbing it with a toothbrush to remove any loosened debris. This simple cleaning fixed both the intermittent connection issues of the switches and keypad.

Another small but annoying issue I encountered was with the stylus’s wired cord. It was damaged. The cord had a deep nick on the inner side of a loop that it had to fold in on, in order for the stylus to fit into it’s receptacle. Because of the location of this damage, it meant that I couldn’t simply just put a layer of heat-shrink tubing over it and call it a day, as it would limit the cord’s flexibility. Which in turn would make it no longer able to fold up and fit into place.

Instead I decided to just replace the entire wire. This lead to the next issue. The stylus’s original wire is somewhat unique. It’s inner structure consists of loose bundles of stranded metal conductors (presumably aluminium) interlaced with plastic (nylon?) fibres. This made it significantly more flexible than any of my wire stock. This flexibility allowed the wire to fold in tight under the stylus when placed into it’s receptacle.

Since I didn’t have an appropriate substitute wire, I decide to just use the best that I had on hand. This consisted of a single line of pure copper multi-stranded wire that was salvaged from an ethernet cable. Since this wire was considerably less flexible than the original, it meant that I could not use the original cable hole to enter the stylophone, if I also wanted to use the stylus receptacle as well. This is because the new cable could not fold into the same tight space under the stylus the old one did. Prioritising the stylus’s use of it’s holder, I decided to just drill another hole for the wire towards the back of the stylophone’s plastic housing.

Now, with regards to the more cosmetic elements of this repair: firstly, I removed and straighten the bent metal grill top plate. I then scraped it and the plastic housing clean of all that yellow hard glue using a scalpel. Ultimately I replaced all the old yellow glue with hot glue after I cut up the grill to fit my additions.

Although as a whole, probably the most noticeable thing about this Stylophone: was the prominent yellowing of the plastic housing. This yellowing is caused by ultraviolet (UV) radiation in sun light. The more sunlight a plastic enclosure like this gets in it’s lifetime, the more yellowed (or even brown) it becomes. Ironically to restore these plastics to their original colouring, one has to use a UV light in conjunction with hydrogen peroxide.

I briefly considered whether or not I wanted to restore the plastics to their original white. And if this was a full restoration project I would have done just that. However this wasn’t the point of this project, since at the end of the day: I was planning to add some crappy home-brew mods to it.

Additionally, I actually rather like the yellowing of older machines. Computers especially. I find it nostalgic. It reminds me of a simpler time: of a young boy listening to the hum of a beige box as it powered on, and the clicking and chittering of the various drives as they promised quality escapism. Insert Sierra logo tune here.

Device Modifications

First things first: for anyone who might raise an eyebrow at my choice of components below, I wish you to know that I basically decided to modify this Stylophone with whatever junk I happen to have on hand at the time. I was unwilling (and somewhat unable) to purchase or salvage more appropriate components for the task.

Not a single part that I put into this machine works as well as they could if I did take the time to source (or install) things properly. However I think that for this particular use-case, such perfectionism is unnecessary. It was just a fun and experimental hack together; and ultimately a learning experience.

With that in mind, I made three simple mods. These were made with the aim to better facilitate my particular use case of this instrument. Something I will explain as I go on.

These mods are:

  • a power indicator
  • an internal speaker cut-off switch
  • and a volume dial for the internal speaker

1) Power indicator

The necessity of an indicator was made apparent to me: when I first picked up the Stylophone to find that I had left it on between sessions, and that the battery was now flat. Now that isn’t to say that the Stylophone definitively uses power when on but not actually playing. I’d need to test whether or not that is the case to say for sure. Either way really, a power status indicator is needed on this device to remind me to turn it off when putting it away. Simple as that.

To install a power indicator, I just used a basic 5mm⌀ red through-hole LED paired with a 330 ohm resistor. I tapped into the 9 volt positive side just after the power switch, and the negative side to the common device ground.

Unfortunately, this resulted in the LED being far too bright for my liking; with a light output that is more applicable for illumination, than as a device power status indicator. I really should have ran some basic ohm’s law calculations on this. Instead I simply used the same resistor value that I was accustomed to pairing with these types of LEDs on the 5 volt circuits that I am used to. Even then, they were rather bright. Now they are even brighter. I should have used a resistor with a much higher value. 1kΩ would likely do for a status indicator on a 9v circuit.

RED 5mm⌀ LED amperage and brightness comparisons

  • maximum continuous amperage: 30mA
  • recommended continuous amperage: 20mA
  • setup I am used to: 5v/330Ω=0.015A (or 15mA) –> reasonably bright
  • current setup: 9v/330Ω=0.027A (or 27mA) –> too bright
  • future amendment: 9v/1000Ω=0.009 (or 9mA) –> perfect for a status indicator

I should state that in my experience using ohm’s law like this is a good guide for component choice. However components are all variable. The vast majority of components all operate within certain tolerances of their stated values. Additionally they can also behave differently once within a circuit.

For example I tested a red LED with a 330Ω (actual value 329Ω) resistor in series on a breadboard and provided it with 9 volts. It’s current draw was 22mA. I don’t really know why. It should still be 27mA. I’m guessing that I am likely not adjusting for something, such as the inline resistance of the breadboard and it’s contacts. Either way, these simple calculations still allow a technician to set their general expectations with regards to component behaviour.

2) Internal speaker cut-off switch

In addition to the internal speaker the Stylophone also comes with an amplifier output socket (3.5mm audio jack socket). I intend to use this socket to sample the audio. Either directly, or via an intermediary signal amplifier of some sorts. This is an alternative to recording using a microphone as you would with an acoustic instrument for example. I think direct sampling like this would produce a cleaner signal, and ultimately better audio.

I added the speaker cut-off switch because I didn’t want the Stylophone itself emitting sound while I was sampling it using a computer. Additionally, since I am likely to be plugged in to PC audio using headphones during the process: the Stylophone playing to the room is unnecessary in this scenario. Hence it might as well be silenced in order to minimised noise pollution and/or disturbance to others.

To make this happen, I just added a switch to the line between the main PCB and the speaker. I decided to use a toggle switch because they are cool. Very simple stuff. That being said, I probably wouldn’t have bothered with a speaker cut off switch if I though of installing the volume dial first. This is because it effectively performs the same function. By lowering the speaker volume to virtually nothing, it does the same job of silencing the speaker.

This was however the first thing that I installed into the device, and I have to confess it was predominantly because I thought that toggle switches were rather neat. I like the tactile feedback of flicking a switch like this, and because of that, I then went looking for a reason to install it into something. I actually almost used two switches like this to replace the two built in slide switches; but decided against it when I saw how they where integrated into the actual PCB itself. Too much work for too little return.

As it is I did notice something interesting about this toggle switch. When flicked off, the signal outputted to the 3.5mm audio jack socket lowers in volume. I think this might have something to do with the cut-off switch taking the internal speaker out of the loop. Perhaps the lower impedance of the speaker coil draws a higher amperage. Which would provide a stronger signal which then would have access to the audio out socket: since it has been place in circuit parallel with the internal speaker.

It’s just a guess, I honestly don’t know why removing the internal speaker from the circuit would result in the signal volume on the audio output lowering. I’ll look into it further when it comes time for a full device overview of this Stylophone. Just for clarity, I should also mention that this does not happen when the internal speaker’s volume dial is set to lower the volume to zero. With it’s potentiometer adding ~10kΩ in series with the speaker in the process. It only happens when the switch cuts the speaker out of circuit entirely. Hmm. :/

  • pins bent to fit space

3) Volume dial

This is probably the only add-on of mine that is actually an absolute necessity in my opinion. Simply put: the Stylophone’s default volume is too loud. It’s tinny high pitched notes can easily come across as obnoxious and irritating at it’s default volume. Especially, when the player is using it to learn by playing the same little tune again and again, and fucking it up half the time.

To install a volume dial, I placed a potentiometer in series with the speaker. That’s it. In this case I used a 10kΩ pot as that’s what I had to hand. Once it came to testing however: it became apparent that I was using less than a quarter turn to effectively move the volume from 100% to 5% volume. With the other approximate two quarters moving the volume from 5% to 1%. Interestingly, the volume never does go down to zero. Even with the full 10kΩ of inline resistance: I can still hear the notes coming out of the speaker faintly. (For context: this pot only rotates to approximately 225 degrees; i.e. to a little under three quarter turns.)

I think this may be the reason why older devices’ volume dials ended with switches. For example with mono-sound CRT televisions: they’d work the volume level with a potentiometer, and then once the volume was below a certain threshold the dial switch would click on to either mute the volume entirely, or switch the device off all together. With that in mind, it makes the unnecessary speaker cut off switch sound almost useful. Eh?

If I were to redo this add-on: I would probably replace the potentiometer, with one with a smaller resistance value range. Maybe a pot that caps at 2500Ω. This is because only the first quarter of the current 10kΩ pot is in effective use, as it represents the most dramatic change in resultant volume.

The main reason why I may want to use a smaller value potentiometer is because it will increase the amount of incremental control the user has over the volume. This increase in precision is caused by adding a larger number of degrees that the dial needs to be rotated in order to increment the volume. Ideally this will result in a full turn of the pot corresponding to the volume scaling accordingly (100% to 5%). As opposed to the current setup of 0 to 90° rotation representing a 100% to 5% volume level, with the other 160° of rotation essentially going to waste.

Another way I could possibly achieve this is by using the same 10kΩ potentiometer and pairing it with a fixed value resistor in parallel in order to bring it’s effective max resistance value down to around the 2.5kΩ I desire. I am honestly not sure how that would work out, as I am only thinking of this while writing. I will experiment with putting resistors in parallel with the potentiometer when it comes time to revise this device.

  • only 1 side of the pot is used

Before & After

Before

After

Video Demonstrations

Mod demo #1

Mod demo v1:

  • internal speaker output
  • vibrato function
  • speaker cut-off switch demo
  • volume dial demo

Mod demo #2

Mod demo v2:

  • power LED
  • internal speaker output
  • vibrato function
  • volume dial
  • speaker cut-off switch

Sound output demo

Sound output demo:

  • external output plugin
  • external & internal speaker dual output
  • internal speaker output
  • internal speaker cut-off switch w/ external output demo
  • internal speaker volume dial w/ external output
  • volume dial unable to mute completely
  • volume differences on external output w/ using speaker cut-off switch

Music demo (internal speaker)

Music demo (external speaker)

Closing thoughts

Ya’know reading back on this: it really is funny how much I could say about so little. At the end of the day all I did was purchase an old Stylophone, clean it up, and then stick a bunch of bullshit in it.

Now, some people may be mad that I did this to such an old device. I noticed that it was made in the 1970’s; and honestly it’s age did give me pause. However I paid very little for this Stylophone, and bought it for the express purpose to tinker with. Additionally, it was literally the cheapest one I could find. Spares and repair condition, economy delivery, no returns accepted. You know the drill.

Also let’s be honest here: not everything old is an antique (e.g. your mum ;)). A mass produced low price point item like this Stylophone is not going to be worth much any time soon. However my innate preservationist did have to hold his breath while I butchered this wee lad. I’ll say that much.

I will be revisiting it, mostly to repair my repairs. To lower the power LED’s brightness, to decrease the volume potentiometer value, and to look into the utility of the speaker cut-off switch. I did have a few other mods in mind as well for it. Such as a 9 volt DC barrel jack socket and power source switch. That way I can run it off a wall charger in addition to battery.

That’s right you heard me. If I am going to butcher a beloved piece of British history, I am going to go all out.

Thank you for reading.

Term glossary

CRT – Cathode Ray Tube
DC – Direct Current
LED – Light Emitting Diode
PCB – Printed Circuit Board
UV – Ultra Violet

Links, reference, further reading

https://en.wikipedia.org/wiki/MIDI
https://en.wikipedia.org/wiki/Stylophone
https://en.wikipedia.org/wiki/Synthesizer
https://en.wikipedia.org/wiki/Voltage-controlled_oscillator

https://www.youtube.com/watch?v=VU7vXMezW_I

[wikipedia]_MIDI_2021-08-31Download
[wikipedia]_Stylophone_2021-08-24Download
[wikipedia]_Synthesizer_2021-08-31Download
[wikipedia]_Voltage-controlled_oscillator_2021-09-17Download

#0032: Instructions on digitising physical documents

Otto

#0032: Instructions on digitising physical documents

Preamble

This will be a quick guide to anyone who may be interested in creating their own digital archives of physical documents. Although there are undoubtedly any number of different ways to achieve this task: I only intend to show you one method. The method that I specifically use (at the time of writing) in order to create, label, modify, and archive document files. Files such as the ones hosted on this website’s “Device Document Scans” page.

Hyperlink: https://www.tinkerersblog.net/device-document-scans

Tools and equipment

Hardware:

  • flatbed scanner
  • personal computer

Software:

  • Linux Mint (operating system)
  • Bash terminal (TUI program for accessing other TUI programs)
  • simple-scan (GUI scanning program)
  • GIMP (GUI WYSIWYG image manipulation program)
  • ImageMagick convert (TUI image manipulation program)
  • img2pdf (TUI file format conversion program)
  • xviewer (GUI image displayer program)
  • xreader (GUI PDF displayer program)

Process overview

1) Scanning the physical document.
2) Initial edit, and virtual file export of scanned images.
3) Edit of image dimensions and watermark application.
4) Creation of alpha-less versions of the edited images.
5) Compilation of all alpha-less images into a single PDF file.
6) Test, organisation, and archiving of files.

Process explained

1) Scanning the physical document.

I use the flat bed scanner on a Pantum M6607NW laser printer scanner combo, in conjunction with a standard GUI GNU/Linux program called simple-scan. One by one I scan all the document’s pages using a 300 DPI (Dots Per Inch) image fidelity setting.

2) Initial edit, and virtual file export of scanned images.

I use simple-scan to export all the raw scanned images in a lossless PNG image file format.

Although simple-scan has some basic image editing functionality, such as image rotation and cropping; I tend to shy away from cropping images here due to the lack of precision available with the tool. However a rough crop to minimize image file size can be useful at this stage. Especially when scanning documents with a smaller page size (e.g. A5); which would otherwise have a lot of needless (memory consuming) white-space in each image.

Additionally, I find that rotating whole images at this stage using simple-scan to be a better experience than rotating them later using GIMP (or even xviewer). This is because, anecdotally: it seems to use less system resources for some reason. It’s just a smoother experience.

As for the outputted files themselves: I like suffixing metadata information onto the file name. In this case “_300DPI_scan”. This is to help identify specific files when they all get archived together.

It also adds a certain element of future-proofing because I may want to create higher or lower DPI versions of the same documents for specific purposes in the future; without it causing a naming conflict, and upsetting my global naming scheme.

Output:

generic_manual_p1_300DPI_scan.PNG
generic_manual_p2_300DPI_scan.PNG
generic_manual_p3_300DPI_scan.PNG …

3) Edit of image dimensions and watermark application.

I use GIMP (GNU Image Manipulation Program) to crop each page image with pixel perfect uniformity (i.e to the same image dimensions). Then I apply my watermark to each page and then export them as PNG images again. I mark the exported PNG files with the ‘WM_’ prefix to differentiate them from the original PNG images, which would otherwise have the same file name.

For the sake of clarity I should state that I keep all the original files (raw scan images) just incase I need to work with them again, and for some reason I do not wish to use the edited versions. It’s good practice to always keep and archive the original unadulterated images for instances like these.

Input:

generic_manual_p1_300DPI_scan.PNG
generic_manual_p2_300DPI_scan.PNG
generic_manual_p3_300DPI_scan.PNG …

Output:

generic_manual_p1_300DPI_scan.PNG
generic_manual_p2_300DPI_scan.PNG
generic_manual_p3_300DPI_scan.PNG …

WM_generic_manual_p1_300DPI_scan.PNG
WM_generic_manual_p2_300DPI_scan.PNG
WM_generic_manual_p3_300DPI_scan.PNG …

4) Creation of alpha-less versions of the edited images.

I use the terminal “convert” program to remove the alpha layers of every PNG image. This is because “img2pdf” can not compile PNG images into a PDF that contains alpha layers. (I.e. clear sections/layers within an image). If you try to, img2pdf will return an error message that contains additional instructions. Unfortunately it will still also output a 0 byte PDF file which you will have to delete.

Error message:

WARNING:root:Image contains transparency which cannot be retained in PDF.
WARNING:root:img2pdf will not perform a lossy operation.
WARNING:root:You can remove the alpha channel using imagemagick:
WARNING:root: $ convert input.png -background white -alpha remove -alpha off output.png
ERROR:root:error: Refusing to work on images with alpha channel

The “convert” command options assigns the background colour to the image as white. This is the colour that replaces any clear (or alpha) sections of the image. Next the alpha sections of the image are removed, then all alpha functionality of the PNG file is switched off.

Please note the exact order that the command options are passed to the program is not important, I only state this order for human understandability. Additionally the “convert” program does not actually convert the original files inputted into it, it instead outputs a modified copy. It will however overwrite the original file if you give the output file an identical name.

I suffix the “_no_alpha” label onto the the outputted files to differentiate them from their predecessors. Although as you can see the file names are getting long and unwieldy, especially if the manual itself already has a long name. However the various prefixes and suffixes all serve a purpose and are necessary for file version distinction.

Command:

convert WM_generic_manual_p1_300DPI_scan.PNG -background white -alpha remove -alpha off WM_generic_manual_p1_300DPI_scan_no_alpha.PNG

Input:

WM_generic_manual_p1_300DPI_scan.PNG
WM_generic_manual_p2_300DPI_scan.PNG
WM_generic_manual_p3_300DPI_scan.PNG …

Output:

WM_generic_manual_p1_300DPI_scan.PNG
WM_generic_manual_p2_300DPI_scan.PNG
WM_generic_manual_p3_300DPI_scan.PNG …

WM_generic_manual_p1_300DPI_scan_no_alpha.PNG
WM_generic_manual_p2_300DPI_scan_no_alpha.PNG
WM_generic_manual_p3_300DPI_scan_no_alpha.PNG …

5) Compilation of all alpha-less images into a single PDF file.

I compile all the watermarked no alpha layer versions of the image files into a single PDF file using “img2pdf” via the terminal.

Command:

img2pdf WM_generic_manual_p1_300DPI_scan_no_alpha.PNG WM_generic_manual_p2_300DPI_scan_no_alpha.PNG … -o generic_manual_300DPI_scan.PDF

Input:

WM_generic_manual_p1_300DPI_scan_no_alpha.PNG
WM_generic_manual_p2_300DPI_scan_no_alpha.PNG
WM_generic_manual_p3_300DPI_scan_no_alpha.PNG …

Output:

generic_manual_300DPI_scan.PDF

6) Test, organisation, and archiving of files.

This stage firstly involves testing if the PDF actually works as expected. Whether or not it is functional and whether or not all the pages contained therein are in the correct order. As well as rendering and scaling correctly. To do this I just try to open the file using Mint’s default PDF viewer program (namely xreader), and skim through the document’s pages.

This stage also involves putting each different collection of images from the various stages of this process into their own labelled ZIP format archive file. Then placing all these files into another container ZIP alongside the ultimate resultant PDF.

It is then placed into the local “device_document_scans” folder. Which is then copied over to the backups. Finally, I also upload the PDF by itself onto this website.

Output:

generic_manual_300DPI_scan.ZIP

Containing:

generic_manual_300DPI_scan.PDF
imageset_no_alpha.ZIP
imageset_raw.ZIP
imageset_watermarked.ZIP

Thoughts on tools and equipment

Hardware

As far as hardware requirements go, its just the bare essentials really: a decent scanner and computer. Neither devices need to be anything special, just fit for purpose.

Computer

As for computers, whatever computer you are currently using is likely to be just fine. The main thing that may become an issue is probably system RAM size; and even then only when scanning large (600+ DPI) multi-page documents at the same time.

This is because the scanning program will have to hold all these rather large images uncompressed within the RAM as you scan through the document. RAM may also become an issue when using image manipulation software like GIMP. If it is too low it may limit how many images you may work on concurrently. At the very lest it may limit your ability to do other things on the machine as you process these images. For example running a RAM greedy application such as a modern internet browser (e.g. Firefox or Google Chrome).

Another thing that may be a limiting factor with computers is CPU processing power. When converting file formats or compiling a series of images into a portable document file: your system may freeze or become unresponsive. Especially if the programs used/running aren’t optimised to be multithreaded. Resulting in the instruction sets all getting queued on the same CPU core and thread. This in turn causes the unresponsiveness as user input is queued behind these instruction sets.

To sum it up, any computer with more than 2-4 gigabytes of RAM and an early generation Intel i3 processor will likely suffice. However there are too many variables that may affect whether or not these system requirements are adequate; such as the desired scan image size, resource use of the operating system, scanning program, as well as background processes.

Scanner

Now onto the scanner. Most if not all modern flat bed scanners should be adequate. Chances are if they connect to your computer via USB 2.0 protocol or better than they are new enough to provide the 300 DPI (dots per inch) image quality that I use for digitising my manuals. If you are scanning photographs you may require a higher DPI rate such as 600 DPI to maximize image detail retention.

However since the value of my manuals is rather utilitarian in nature, 300 DPI is a fine image quality for my use case. By ‘utilitarian’ I mean that the information printed onto the manuals is what I am primary preserving, and not each page’s visual aesthetic. Because of this I just need them to be legible without necessarily preserving every minute page detail.

Heck, an argument could even be made to go down to a 75 DPI scan setting: as it’s perfectly useable whilst also minimizing all file sizes; including all intermediary portable network graphic images, as well the final portable document file.

However I find that working with 300 DPI images (which translate to a maximum of 2550*3507 pixels for an uncropped full scan) are a good compromise between image detail and workability/use-ability.

Example of 1200 DPI scanned image unable to be displayed with xviewer

Scan DPI example files

example_0075DPI_scanDownload
example_0150DPI_scanDownload
example_0300DPI_scanDownload
example_0600DPI_scanDownload
example_1200DPI_scanDownload
example_2400DPI_scanDownload


(Feel free to download and test these files on your own system.)

Scan image metadata translations

(Translations based on a scan of the full scanner bed of a PANTUM M6607NW)

Key: scan quality (Dots Per Inch) / image dimensions (pixels) / file size (bytes)

  1. 75 DPI / 637*876 p / 870.9 kB (lossless PNG)
  2. 150 DPI / 1275*1753 p / 4.2 MB (lossless PNG)
  3. 300 DPI / 2550*3507 p / 17.5 MB (lossless PNG)
  4. 600 DPI / 5100*7014 p / 62.8 MB (lossless PNG)
  5. 1200 DPI / 10200*14028 p / 211.9 MB (lossless PNG)

Software

Since my operating system of choice is Linux Mint running the Cinnamon desktop environment, I just use the programs that are either available with the initial install package as standard; or downloaded from the standard Ubuntu repository if necessary.

Simple-scan comes preinstalled with Linux Mint. It is the default scanning utility program. There are more robust alternatives such as ‘xsane’; however my philosophy with regards to tools like this is that one only upgrades tools or seeks alternative tools when the default tools are found to be wanting. I.e. when there’s a particular functionality or quality that the current toolset doesn’t provide; and since the default simple-scan program provides adequate functionality, I don’t need to seek alternatives just for the sake of it.

Moving on. Both GIMP, Image Magick and ‘img2pdf’ are available within the standard Ubuntu software repository. So both can be downloaded using the ‘sudo apt-get install’ commands. However it is recommended that you first use “apt-cache search [program]” command to ascertain whether or not they are available within whatever repository that you are using, if you are using another Linux distro to Linux Mint.

sudo apt-get install gimp
sudo apt-get install imagemagick
sudo apt-get install img2pdf

To sum up GIMP. If you are coming from Windows, you may be used to other image manipulator programs like ‘paint.net’ or ‘Adobe Photoshop’, if not GIMP itself since it is a multiplatform program and available on Windows. Anyway if you have used any modern full-suite WYSIWYG image manipulation program, then GIMP will be an easy enough program to jump on to.

Finally Image Magick. This is a software toolkit that you access via the Bash terminal. Many people, including myself prefer TUI based programs like this due to their ease of use, user interface uniformity, and functional robustness.

I often write scripts including commands that utilise programs that can be accessed via Bash. The programs provided by Image Magick are no different. Once a person gets used to using them, it becomes a natural progression to create scripts which then automate the process.

This would be useful for situations such as batch conversion of multiple files: as scripting allows the user to go AFK or do something else, rather than babysit the process. Scripting and chaining commands like this is probably the greatest strength of CLI/TUI programs over GUI programs.

Closing thoughts

If you aren’t already accustomed to using any Linux based distro, then one thing I recommend keeping in mind is hardware compatibility. It is probably this platforms biggest weakness.

This is specifically because most companies build their products to target the Windows platform. Often facilitating device functionality by using proprietary drivers, and oft times even programs: such as with proprietary controller programs for LED keyboards. These drivers are sometimes absent in Linux. However in most cases there are open-source alternatives.

In the past this used to be a bigger issue. Thankfully the list of supported peripheral devices has gotten much better as of late. As it is at the time of writing, and according to my personal experience as well as as some online reading: most devices work flawlessly plug-and-play; however, some devices work for the most part but are missing some advanced functionality, and some devices don’t work at all.

Unfortunately the best way to tell whether or not your device will work, is by simply plugging it in and fiddling with settings and open source drivers; until it either eventually works, or you give up. Whichever comes first.

As an example: I had quite a few issues with my system not recognising my Pantum M6607NW printer-scanner combo properly, despite official Linux drivers being available on the standard repository, and via the companies website. Even now, after resolving that problem and getting the thing working, I am still having some minor issues with the device.

For example if you paid attention to the images above, you may have noticed that Simple-scan allows for a 2400 DPI scan in conjunction with the Pantum M6607NW. Unfortunately this setting doesn’t work as expected. It does scan the document, and it does it noticeably slower than on the 1200 DPI setting. Which is as expected, due to scan heads collecting more detail from each page segment. However the resultant image has the same pixel dimensions as a 1200 DPI scan. So if there is a higher detail density, it isn’t reflected in a larger image dimension – as is the case with all other DPI settings.

Although xviewer failed to open images of this size, the Firefox browser did not; and upon visual inspection and detail comparison between the 1200 and the 2400 DPI scans: I have concluded that they are identical. See for your self, the files are listed in this article. Knowing this, it is likely that simple-scan is providing an option that the scanner can not support. Although the Pantum’s slower read speed on the 2400 setting has me doubting this conclusion. Since it seems to exhibit a programmed hardware response to this setting.

I could likely find the solution eventually by combing through the official generic M6600 series online manual for my machine, then hunt down more specific documentation … although it is frankly not a priority at this point. As I am not planning on using a 2400 DPI scan setting anytime soon. I only highlight this specific issue to make you aware of the kind of troubleshooting fun to expect on this platform.

So if you are moving to a Linux based platform for productivity purposes, well you can’t say that you haven’t been warned. Having said that, don’t let that stop you from using this platform for this purpose. When it works it works fantastically, and when it doesn’t there is always something that you can do yourself to make it work. You have to get used to being your own tech support.

Best of luck archiving your documents, and as always:
Thank you for reading.

Glossary of terms

AFK: Away From Keyboard
Bash: Bourne Again SHell
CLI: Command Line Interface
DPI: Dots Per Inch
GIMP: GNU Image Manipulation Program
GUI: Graphics User Interface
PDF: Portable Document File
PNG: Portable Network Graphic
PnP: Plug and Play
TUI: Text User Interface
WYSIWYG: What You See Is What You Get

Links, references, and further reading

man_bashDownload
man_convertDownload
man_gimpDownload
man_imagemagickDownload
man_img2pdfDownload
man_simple-scanDownload
man_xreaderDownload
man_xviewerDownload