Arduino-based tempo/expression pedal

[ElectricDruid]

I think I won't bother dealing with finding the right PIC for this and order it now: Says back-ordered, how much time would it take to ship?

We must have run out of programmed ones. We've got more blanks, so we'll program some up and it won't cause a delay.
 

Quick question on the schematics that, whats the use of J letters? Especially on the Tap Tempo where there's a button already?

The J letters indicate points where offboard connections would go, input, output, power, ground, stuff like that. The Tap Tempo one can have an external sync input.

[Baran Ismen]

I think I won't bother dealing with finding the right PIC for this and order it now: Says back-ordered, how much time would it take to ship?

We must have run out of programmed ones. We've got more blanks, so we'll program some up and it won't cause a delay.
 

Quick question on the schematics that, whats the use of J letters? Especially on the Tap Tempo where there's a button already?

The J letters indicate points where offboard connections would go, input, output, power, ground, stuff like that. The Tap Tempo one can have an external sync input.

All good. I've prepared a schematic for my understanding and preparing a PCB for it, can you check quickly? Especially the rotary switch section. It may need different resistors as I built up the whole circuit over 3.3V instead of 5V.

[ElectricDruid]

Various comments:

1) R6 should be connected to the other end of R7.
2) If you're not using the external sync input, you don't need Q1 and D2. They can go.
3) Rather than use D1 as a "parallel diode" to protect against reversed power supply, you could put it in series with R1. After all, it's not like you care about a little bit of voltage dropped across the diode when you're about to step down from 9V to 3.3V. In fact, it would *help* a little bit, since the voltage regulator won't have to lose so much. It would also be better for the power supply in the event that you do connect one that is reversed (it won't short it with 330R).
4) The value of R10 is 100K in the original StompLFO schematic, but...
5) ...R9+R10 and R3 make a voltage divider to ground that will cut *a lot* of signal. You might be better altering the values of the filter so that instead of using 10K/47n/100K/4n7 you use 1K/470n/10K/47n. That changes the divider to 1K+10K/100K which will only lose 10% or so (assuming no further loading from the circuit you plug this into).

In general, it looks fine and these are only tweaks.

[Baran Ismen]

1) R6 should be connected to the other end of R7.

Done, changed.
 

2) If you're not using the external sync input, you don't need Q1 and D2. They can go.

Done, removed.

3) Rather than use D1 as a "parallel diode" to protect against reversed power supply, you could put it in series with R1. After all, it's not like you care about a little bit of voltage dropped across the diode when you're about to step down from 9V to 3.3V. In fact, it would *help* a little bit, since the voltage regulator won't have to lose so much. It would also be better for the power supply in the event that you do connect one that is reversed (it won't short it with 330R).

Done, I guess. Still not handy with how diodes work, lol...

5) ...R9+R10 and R3 make a voltage divider to ground that will cut *a lot* of signal. You might be better altering the values of the filter so that instead of using 10K/47n/100K/4n7 you use 1K/470n/10K/47n. That changes the divider to 1K+10K/100K which will only lose 10% or so (assuming no further loading from the circuit you plug this into).

Done. The last R3 you mentioned (now changed) is actually there for shorting the tip to ground. I've discovered that it works flawlessly when tip & ring are shorted directly and tip is also shorted to ground with 100k resistor (as suggested before)

Here's the updated schematic.



 

[ElectricDruid]

Done, I guess. Still not handy with how diodes work, lol...

It would *work* perfectly the way you had it. It's just that there are some reasons for having it this way instead.

The last R3 you mentioned (now changed) is actually there for shorting the tip to ground. I've discovered that it works flawlessly when tip & ring are shorted directly and tip is also shorted to ground with 100k resistor (as suggested before)

Understood.

Here's the updated schematic.

Looks good to me. I spotted one more minor thing: If you have C5 next to the StompLFO, you don't need C3 next to the regulator. I mean, you *might* if it was a massive circuit board with tens of centimetres of traces between one and the other, but this will be small, so there's no need.

[Baran Ismen]

Done, I guess. Still not handy with how diodes work, lol...

It would *work* perfectly the way you had it. It's just that there are some reasons for having it this way instead.

The last R3 you mentioned (now changed) is actually there for shorting the tip to ground. I've discovered that it works flawlessly when tip & ring are shorted directly and tip is also shorted to ground with 100k resistor (as suggested before)

Understood.

Here's the updated schematic.

Looks good to me. I spotted one more minor thing: If you have C5 next to the StompLFO, you don't need C3 next to the regulator. I mean, you *might* if it was a massive circuit board with tens of centimetres of traces between one and the other, but this will be small, so there's no need.

Thanks for everything, Tom! I do appreciate much! Now I'll wait for the chip to arrive.

Here's the latest layout and PCB I've drawn. If needed, you (or anyone) can use it as a reference for those who want to make a project like this. It's my first time drawing such a complicated PCB from a schematic, so please go easy on me