MarkT

Check the USB cable isn't a just a charging cable - #1 problem people have...

These two synths were built about a year or so apart, both controlled by Teensy 4.1 chips at their hearts, the Teensy manages MIDI, the front panel, voice assignments, arpeggiator functions, patch memory on SD, keyboard and modulation.

More info on why its bad to slug CMOS inputs with an RC filter: https://www.ti.com/lit/wp/slla364a/slla364a.pdf

Also using an RC filter places the input voltage in the forbidden region for significant periods which can drain a lot of power on a low power CMOS system. Though the T4 isn't very low power of course.

You forget that a slow moving signal to a logic input may make dozens or hundreds of transitions anyway due to the high gain of an input buffer - the simplest way to handle the bouncing is poll the signals at a sensible rate like 1kHz - then high...

Ever used a debugger with templated code? Or worse with STL classes? Heavy obfuscation is commonplace.

Paragraphs exist for a purpose! A large block of text like that will put people off reading it.

Are the switches remote or close to the Teensy? If close the internal pullups will be enough, else add external pullups. Capacitors wouldn't help I don't think.

Either version requires you to have relevant page of the datasheet to understand - if your field names were readable then it would be better, but probably multi-line! Perhaps best to wrap all the register encoding in functions/macros with well...

Suspicious of this, the 2222 is actually slow compared to logic speeds (try reducing the base resistor to 1k though), and not push-pull (totem pole). A 74HCTxx gate would do the job properly as they run at 5V and are 3.3V input compatible. You...

And note there are also capacitors in series with many signals, so DC and AC impedances are different!

It is a structural error, whether benign or not it should be fixed to prevent confusion in the future...

I find it usually much easier (quicker) to use explicit hex constants so that the code can be compared to the information in the chip datasheet register diagrams directly - naming every little field in every register is not always a good thing...

Yes I think so - Schottky diodes are better due to their lower on-voltage. You might want to bias the input to mid rail rather than ground though.

The incredible ZTX751/851 and similar super-beta devices have ~50mV saturation voltages if you ever have to drive a heavy load or need a smaller package size.

Or its simply been X-rayed in transit? Cargo X-raying apparently uses very high X-ray energues to penetrate the steel shipping containers and this can be enough to disrupt electronics.

Maybe a medical-grade USB supply?

Series resistors (around 22 to 100 ohms often) damp reflections/ringing on fast logic and thus stop double-clocking which can cuase malfunctioning, particularly for clock signals - they are not doing a lot for EMI though. Think of this as like...

For using a BJT as a switch the hFE value is not relevant - that applies only to the active, linear area of operation (where the collector-emitter voltage is significantly more than one diode drop). Switching uses cutoff and saturation modes...

More flux; less solder.... Silicon devices are very robust to high temperatures. Back in the days of germanium devices this wasn't so and it was easy to cook a device, but silicon devices, unpowered, can usually tolerate higher temperatures...

Yes, 1N4148 handles 75mA, the relay uses 12mA, not a problem. Base resistor for the 2N3904 should be about 2k2, giving > 1mA into the base. For switching make the base current about 10% of the load current. The hfe is not relevant to switching...

1) LEDs will produce heavy switching noise as they have logic-fast drive and take a lot more current than a logic signal (think ~100A/µs current slew rates!) - keep separate from analog stuff by distance, avoid large loop area in the current...

Some more progress. I have now added more Teensys :-) the synth is now 8-way multi-timbral, had independent arps for each channel, plus drum machine channel. I also added foot controller (based on basic Arduino Mini) that sends MIDI to main...

Common mode noise is ignored by a differential receiver, that's why they are used for encoders in industrial environments. If the differential mode signal is clean there is no problem.

If they are differential you need to look at the differential mode noise, can you use math mode to plot the difference and see what the true differential noise is like?

Can you swap the cables to see if the problem moves with the old cables? Do the noisy channels have wiring that runs next to high power cabling? Are the encoders differential? If so that level of noise isn't a concern unless its...

Four NiMH's in series make a 5V supply that's rechargable in-place with care - NiMH are about 1.3V each charged, dropping to 1.15V or so when drained, giving 5.2V down to 4.6V. NiMH has no fire risk either.

With high density expansion connector comes: flexibility