FV-1 and tap

[DIY Bass]

Hi, I am thinking about getting and building one of the PedalPCB FV-1 boards to play with.  Just for the heck of it really.  I had thought that adding in a tap footswitch would be pretty cool, and I have seen that people have implemented the software to be able to do tap tempo, so it is plausible.  I know that you add in a switch in place of one of the control pots in order to make it happen.  I would like to be able to keep all 3 pots for use in some patches though.  I was thinking about a switching mechanism (3pdt switch should be able to switch in a switch in place of a pot).  I do wonder though about just putting a momentary switch in parallel with the pot.  I guess maybe you would need to have the pot turned down to zero in order for it to be reliable, but with that done and the switch between the input and 3.3v is there any reason why you couldn't just use it as a tap input, without needing an extra switch?  Any better ideas about how to do it?

[potul]

Both approaches would be fine, but if you put the switch in parallel to the pot, you must add some resistor to avoid shorting Vcc to Ground when the pot is at min.

[potul]

This is how I did it last time:

Code Select Expand

  Vcc           Vcc
   |            |
   |            |
   |           \
   |            \
   /     100K   |   
   \<---/\/\/\------FV1
   /
   \
   |
   |
  GND

When the footswitch is open, the 100k resistor is not affecting much the reasing of the POT. When you close the footswitch, the POT input in the FV1 will be high, and the 100k resistor will prevent shorting to ground.
You need to keep your pot at minimum to make it work (it depends on the software, you can make it work even if not in the min)


This has the added bonus that you can use the footswitch to max your pot. I use it for maximum reverb, oscillating delays, etc...

[Digital Larry]

You can also use one of the audio inputs for tap detection, assuming you are only using mono in.

[DIY Bass]

You can also use one of the audio inputs for tap detection, assuming you are only using mono in.

That is interesting, because the pedal pcb boards are mono in, so the extra input I assume is just grounded.  That would have the advantage of still being able to use all the pots as well.  Do you just switch the input to Vcc?  I assume the software side is similar?

[Digital Larry]

You can also use one of the audio inputs for tap detection, assuming you are only using mono in.

That is interesting, because the pedal pcb boards are mono in, so the extra input I assume is just grounded.  That would have the advantage of still being able to use all the pots as well.  Do you just switch the input to Vcc?  I assume the software side is similar?

I would always use a pull up and switch to ground.  I'm not sure if there's any real benefit to that compared to pulling down and switching to Vcc other than you don't put Vcc on a wire to a switch which is maybe arguably safer.

Ground for the analog in is interpreted as -1.0, so you'll have to make some accommodation in code, I'd think, compared to using a POT input.

[DIY Bass]

You can also use one of the audio inputs for tap detection, assuming you are only using mono in.

That is interesting, because the pedal pcb boards are mono in, so the extra input I assume is just grounded.  That would have the advantage of still being able to use all the pots as well.  Do you just switch the input to Vcc?  I assume the software side is similar?

I would always use a pull up and switch to ground.  I'm not sure if there's any real benefit to that compared to pulling down and switching to Vcc other than you don't put Vcc on a wire to a switch which is maybe arguably safer.

Ground for the analog in is interpreted as -1.0, so you'll have to make some accommodation in code, I'd think, compared to using a POT input.

So just to clarify and make sure I understand - you are suggesting having a resistor (say 100k?) between the input and Vcc, and a switch to switch the input pin directly to ground?  Or does the switch go on the other side of the resistor?  Now I think about it I am leaning towards option 2.

[Digital Larry]

So just to clarify and make sure I understand - you are suggesting having a resistor (say 100k?) between the input and Vcc, and a switch to switch the input pin directly to ground?  Or does the switch go on the other side of the resistor?  Now I think about it I am leaning towards option 2.

Yes.  Put a resistor between Vcc and the input pin, so under normal circumstances the voltage on the input pin is Vcc.  Then connect a momentary switch to ground at the input pin, so that when you press the button, the input is now at ground level.  This makes detection fairly easy, as when it's open it's "way" above zero (zero is in the middle for audio signals) and it's "way" below zero when the switch is closed.

Note that the actual input voltage will depend on the input impedance and the pull up resistor.  100k will probably work, I think the FV-1 input impedance is 20k?  But you'd have better noise immunity with 10k or 4.7k.

DL

[DIY Bass]

10k it is.  I have looked at the pedalpcb schematic and it looks as if the 2 inputs are tied together.  I expected the unused one to be grounded, but it isn't.  I was intending to order the board with the chip pre-soldered, because it doesn't cost much more.  I have soldered SOIC before but never as many pins or as expensive a chip.  I will see how easy it is to break that link with the chip in place, and will go with the parallel to pot option if it looks too hard.  Will just depend on how the routing is done.  Thanks for your help.