Spin Semiconductor

I'm looking into laying out a PCB for a tap tempo delay using a momentary switch to control the tap on one of the control pins but also want to use a pot on the same control pin for manual adjustment of the delay.

What would I need to consider hardware wise. The issue that first springs to mind is with the pot set to either of its extremes say 3.3v at the wiper, stomping on the switch connected to the same control pin to ground will cause a short. Is there anything else I need to watch out for.

You can isolate the pot so the switch won't cause a short, run two resistors in series between the pot wiper and the pot input, your switch goes to the junction of the two resistors. This is what I do in my babelfish, copied from the guitar amp appnote.
The other issue is, say your switch is to ground, if the pot is turned all the way down, the input is already grounded so the switch won't do anything. You could, put a resistor between the bottom of the pot and ground, so in effect the pot doesn't turn all the way down. Your code can then dedect when the switch pulls the input below this level.

Thanks Slacker, that's exactly the info I was looking for. I had found the info on the split resistor to switch in the guitar app schematic which was also in one of your posts relating to tap tempo that I found, but I was not sure how to tackle the pot to ground issue. Cheers.

I'm thinking of using the 8 eeprom programs for different tap settings rather than pot skip routines and a separate pot for mix, which would leave me with a spare FV-1 pot to use maybe for a tone/filter control on the feedback. Just a thought.

slacker wrote:You can isolate the pot so the switch won't cause a short, run two resistors in series between the pot wiper and the pot input, your switch goes to the junction of the two resistors. This is what I do in my babelfish, copied from the guitar amp appnote.
The other issue is, say your switch is to ground, if the pot is turned all the way down, the input is already grounded so the switch won't do anything. You could, put a resistor between the bottom of the pot and ground, so in effect the pot doesn't turn all the way down. Your code can then dedect when the switch pulls the input below this level.

I'm using this too, you need to find the both ends of the pot that makes the switch work, put some resistors so the pot reaches both ends and then in the FV-1 adapt the scale for a full range.

You could also use an SPDT switch.

Digital Larry wrote:You could also use an SPDT switch.

Code: Select all

               /o-------- Pot wiper
FV-1 ------o/
                o-------- Ground

Yeah, but if the pot wiper is near ground the switch doesn't affect anything and you can't detect if the ground (or near ground) is because the pot it's near 0 or the switch is pressed.

Sweetalk wrote:
Yeah, but if the pot wiper is near ground the switch doesn't affect anything and you can't detect if the ground (or near ground) is because the pot it's near 0 or the switch is pressed.

You got me there!