DIY keycaps

 I'm trying to make some keycaps for the Cherry ML that are smaller than the standard square ones. My first try was mildly successful:

These were made using 0.8mm matte black acrylic. The text is engraved while the outline is cut. On the one with text, the hole has been cut as well, and we can see that it got too hot - the thin part below the hole is bent. 

On the second one, the hole has been made by engraving 6-7 times. This generates a lot less heat. Unfortunately, I chose to cut the outline afterwards, which made the thin part bend again. I think that cutting first, then engraving, would solve the problem.

I intend to mount the 0.8mm on top of a 3-4mm clear acrylic piece. It would also be worth trying to glue the pieces first to see if the cut gets better. I could then engrave the hole and stop once I reach the clear acrylic.

The text will be filled with white Lacquer-Stik.

I will glue the keycap on top of a fastening mechanism from other keycaps. The only issue is to get a good bond between the acrylic and the ABS which the keycap is probably made of. I've found a glue that promises ok results - Acri Bond 120.

Finally, I did the cutting with less powerful settings than our laser manual states.

3mm clear/black: speed 40, power 100

0.8mm black: speed 100, power 100

VCO retesting and more detailed sync tests

 I retested the PW on my VCO and discovered that I had forgotten to ground two points. After fixing this, my own PWM works fine without pitch dropping.

I also did a more thorough test of various sync modes:

CEM Hard sync

- Datasheet says to sync against pulses, 1volt minimum, 3v maximum

In practice in my circuit

- Needs 1nF input cap

- Square wave with 50/50 duty cycle, +/-5v works fine.

- Saw wave, rising +/-5v works but only gives half sync

- Saw wave, falling +/-5v works but only gives the other half sync, and weird (but cool) behaviour when synced oscillator frequency is higher than master.

- Amplitude and offset of sync signal does not affect it.

- Strongly affected by PW, not in a good way

Conventional HS

- Datasheet says to use -negative pulses only, 8-10V

In practice in my circuit

- Saw wave, rising, +/-5v works. Falling does not work

- Square wave with 50/50 duty cycle, +/-5v works just like saw wave (but saw wave has a slight clip on top)

- Square wave with other duty cycle than 50% does not work well.    

- Not affected by offset

- Affected by amplitude, +/-5v works best

- Strongly affected by PW, not in a good way

CEM Soft sync

- Datasheet says to use negative pulses, max 5V

In practice in my circuit

- Needs 1nF input cap

- Square wave with 50/50 duty cycle, +/-5v works fine

- Saw wave, +/-5v, rising and falling works fine and sound the same, has a darker tone than square wave???

- Strongly affected by PW, not in a good way

Sync circuit conclusion

- I think I should build at least the prototype voice card with selectable saw, inverse saw or square wave input. 

- All waves should be +/-5v

- Waves should be tapped pre-VCA/mixer. Square should have its own square wave generator that is unaffected by PW and pulse VCA.

- I should give the option to switch between all three modes - to see how it sounds in practice

- I seem to remember that there was talk about constant frequency offset vs constant pitch offset in syncs, maybe worth investigating (but is a software issue, not hw).

LED ring update

 I got some work done on testing the LED ring with the MAX7221 7 segment encoder today, and the results are great. Both single led and multi led indicators are feasible and each has its own use. 

I tried with various lenses but my current conclusion is that no diffuser, red lense and a black panel definitely looks the best. Using a diffuser only made it look muddy.

The MAX7221 greatly simplifies the design/code. Multiple ICs can be chained, and I also think multiple parallel devices on the SPI bus are possible. One IC covers two pots with 32 leds.

I also got some amazingly good looking knobs today, matt aluminum, no indicator. Unfortunately, they have knurled, not D shaft, so it may be hard to find an endless potentiometer to fit it.

Great looking encoder knobs!

I've ordered a bunch of various knobs lately. I'm trying to find some that work with endless potentiometers/encoders, preferably D-shaft. It's harder than you'd think - most cheap knobs are for knurled/flower shafts, and almost all have some kind of groove or print to indicate position, which I guess almost everyone want.

It's really hard to tell from the photos on ebay and aliexpress etc if the knobs have an indicator, and sometimes they even try to hide it. Today I got the first delivery, and lo and behold - they look amazing! Just what I was looking for. Black spun  aluminum, D-shaft with no indicator! 

Here is the original description:

https://www.aliexpress.com/item/32924107059.html?spm=a2g0s.9042311.0.0.56d34c4dRi6Wum

Breadboards - distance between power busses

 I am making some utility boards for breadboard power supplies and i/o. 

This means I have to know the exact dimensions of the breadboards. 

The senter piece is easy - holes are about 0.1" apart (though measuring the exact dims it seems that they are often a little off, just not enough to be a problem). In addition there are two holes missing in the middle. Distance between the two outer holes is then 1.1" or 27.94mm.

By looking at the cards I expected the same to be true for the distance between the columns and the horizontal "busses", after all, this would seem the reasonable thing to do. But this turned out to be a mistake! 

I did some googling, and found a site that showed a board that had the distance between the outer busses as 1.85" (the expected would be 1.9 if all holes were 2.54" apart).

I then made my cards to this standard, but when doing a test print, this turned out to be too little... The busses on MY breadboards at least are further apart. To make things worse, there are differences between cards that look similar but are from different vendors/orders ("luckily" there is also differences in the spacing of the tabs that connects the cards so cards from different batches cannot be connected properly - making it easy for me to know what cards are from what batch).

So, I have to take some accurate measurements to figure out what is going on.

Here are the dimensions of my two batches of boards:

A: Power busses: 9.40mm, main part: 35.45mm, total w/gaps: 54.58mm

- gaps are 0.17mm

- padding around busses is 3.43mm per side

- padding on main part is 3.76mm per side

- calculated distance between outer bus lanes is 47.74mm = 1.879 inches

B: Power busses: 9.45mm, main part: 35.5mm, total w/gaps:54.64mm

- gaps are 0.12mm

- padding around busses is 3.46mm per side

- padding on main part is 3.78mm per side

- calculated distance between outer bus lanes is 47.74mm = 1.879 inches

Wow, that was a bit surprising. Even though things looked very different, the inaccuracies evened out to make the end result equal for both batches. With the pretty lose tolerances in the making of these cards, I'd say that 1.88 inches is probably the distance to aim for. Measuring using digital callipers give a very similar result for both cards. 

As for the bus distances between cards with two and tree busses between them, they should be:

2 busses (four lanes) - distance between outermost lanes of each card: 

A: 2 * 3.43mm + 0.17mm = 7.03mm

B: 2 * 3.46mm + 0.12mm = 7.04mm

0.275 inches is 6.99mm, which is a good approximation

3 busses (six lanes) - distance between outermost lanes of each card:

A: 2*3.43mm + 0.17mm + 9.40mm = 16.43mm

A: 2*3.46mm + 0.12mm + 9.45mm = 16.49mm

0.65 inches is 16.51mm, which is a good approximation