Momentary Guitar Footswitch Mode Toggle Modification

Question

Hi Guys,

I am learning as I go here and I have set myself a challenge...

My guitar amp is switched by a 4 button footswitch all switches are momentary and the channel switching logic is done (I believe) in the amp by a pulse to ground over each switch.

Clean, OD1, OD2 & Reverb

The footswitch is connected over a DSub9 and the pinouts (from memory) are:

1 - Clean LED Anode

2 - OD1 LED Anode

3 - OD2 LED Anode

4 - Reverb LED Anode

5 - 0v

6 - Clean

7 - OD1

8 - OD2

9 - Reverb

What I'd like to do is repurpose the switch on OD2 for something else, so I was thinking I could use the OD1 switch as a toggle between OD1 & OD2 modes. The research I've done has led me to believe that I can do this by using a combination of JK Flip-Flop and 556 (or 2x 555) timer as a one-shot monostable:

Here is my circuit, is this right? What's missing and what resistor values do you suggest I use to with the 10uF polarised caps I'm going to use to allow a very quick pulse (HIGH) from the 556?:

The 556 outputs will go to a pair of NPN's (not LED's as shown) that will pull the pins 7 or 8 to 0v (pin 5)

jc2048 · Answer

Starting at the beginning, the switch will almost certainly bounce when you press it. [The contact, instead of landing cleanly, bounces and then breaks and makes a few times before settling. If you have an oscilloscope, wire up just the switch and the resistor and capture the waveform.]

So you'll probably need to debounce the switch to stop it clocking the flip-flop more than once.

Here's what an old momentary toggle switch that I fished out of a spares box looks like on a 9V supply with a 10k down to ground.

Momentary Guitar Footswitch Mode Toggle Modification

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