Circuit question

[giff25]

How does the snare avoid noise over a shared 3.3v line on a max velocity hit?

I am trying to extend prototype 2 to 10 piezos and ive gotten most of it down, except I keep getting false triggering over other channels that share the 3.3v line (im assuming this is because the excess voltage from the hit is being dumped through the schottkey diode then into 3.3v line then to other channels).

I want to check if this is intended and accounted for or if I did something wrong.

[3hhh]

On Thu, 26 Mar 2026 06:19:59 -0700 Victor Butkov ***@***.***> wrote: giff25 created an issue (corrados/edrumulus#179) How does the snare avoid noise over a shared 3.3v line on a max velocity hit? I am trying to extend prototype 2 to 10 piezos and ive gotten most of it down, except I keep getting false triggering over other channels that share the 3.3v line (im assuming this is because the excess voltage from the hit is being dumped through the schottkey diode then into 3.3v line then to other channels).

So you believe that your micro controller cannot hold 3V3 against a piezo current? I don't think that's the root cause, but you could probably check with a secondary power source.

I want to check if this is intended and accounted for or if I did something wrong.

I recall that I had similar issues in the beginning though. For me back then the root cause was that I had apparently fried the ADC during one of my tests and it had started to see phantom voltages from previous reads etc. You may also have chosen the wrong diodes: For example p-n diodes usually have a forward voltage of 0,6-0,7V meaning that there may be up to 4V at the 3V3 input. Micro Controllers however often have a +-0,3V acceptance range for their 3V3 power, i.e. stuff may break... Schottkies in turn usually are within that 0,3V forward voltage range. Using a fast Schottky should also help. Then it may also be loose or unstable connections. I had much more issues with a breadboard than with a printed circuit. You can also try to dampen the snare by increasing the resistance in series, i.e. R1/R3.

[3hhh]

Another possible reason I forgot: It may also just be cross-talk caused by you playing your pads. Move them far away from each other to make sure it's not that. There are software means to fix such cross-talk though (see my xtalk repository).

[giff25]

The problem isn’t that it’s not holding the current. When I’m measuring a different input channel (input wire that goes from a different piezo on the snare to its respective input pin) I get an “echo” over the 3.3v rail. As a result the other piezo is acting as if it was hit. Is this crosstalk? If so I thought crosstalk was from the physical vibrations affecting the piezo

[3hhh]

On Thu, 26 Mar 2026 11:15:29 -0700 Victor Butkov ***@***.***> wrote: giff25 left a comment (corrados/edrumulus#179) The problem isn’t that it’s not holding the current. When I’m measuring a different input channel (input wire that goes from a different piezo on the snare to its respective input pin) I get an “echo” over the 3.3v rail. As a result the other piezo is acting as if it was hit. Is this crosstalk? If so I thought crosstalk was from the physical vibrations affecting the piezo

Yes, cross-talk should be from physical vibrations only. Anyway what you're describing sounds like your ADC broke as well from overvoltage. You might be able to devise some sanity tests for your ADC to verify that. Or just try another microcontroller. Any other thoughts @corrados?

[giff25]

I’m not measure from an and ADC, I’m using a multimeter and I’m getting consistent result so It’s highly unlikely it’s from measurement error

[giff25]

To update, I found that most people use a bypass capacitor to "shunt" noise to ground over a shared voltage source. I will try putting it next to the positive 22kohm resistor.

[3hhh]

On Mon, 20 Apr 2026 10:54:36 -0700 Victor Butkov ***@***.***> wrote: giff25 left a comment (corrados/edrumulus#179) To update, I found that most people use a bypass capacitor to "shunt" noise to ground over a shared voltage source. I will try putting it next to the positive 22kohm resistor.

Yes, please keep us posted on that topic. It may be relevant for future designs.