Replacing a momentary contact switch with a piezo switch in audio amplifier power relay circuit

Thread Starter

rsaumure

Joined Dec 29, 2019
4
Hi, pretty much a total noob here so please bear with me.

I like learning new stuff, and get the most benefit with little hands on experience. With the encouragement of my wife I started down the diy audio path. Found I really enjoyed soldering stuff together and learned a little in the process. Attached is a circuit that operates a power relay for an audio amplifier ( and has a thermal cut-out in case it over heats ) The circuit is controlled by a NO momentary switch. This is built and operates as it should. What I really really want to do is replace the NO momentary switch in the circuit with the langir piezo switch and am looking for the simplest most reliable way to do this. If I wire the piezo switch into this circuit, the piezo can power off the circuit, but it will not turn it on. I have tried the piezo on other circuits that require momentary contact and it does work but I suspect that is because the other circuit pushes like 12 volts across the piezo. I have read about using a piezo with an FET or using an op amp to make the piezo behave like a momentary contact switch. Do you see any way to possibly change some of the resistor or capacitor values that would allow the attached circuit to function with the piezo switch? Trying to keep it simple yet at the same time reliable. Much thanks!
 

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Thread Starter

rsaumure

Joined Dec 29, 2019
4
The power circuit I attached in my original post "turns on" a relay when a momentary switch is pressed. I believe your picture is the latching version of a piezo switch. What I am trying to do is replace the momentary contact switch in the circuit with a piezo switch. I think this is what I am trying to do:
1582569700888.png
 

Delta prime

Joined Nov 15, 2019
504
This is what's going inside of your Piezoelectric switch
R1 is your off resistance.
R2 is your on Resistance
It is an active device and is why you need 12 volts for it to work.

piezo-switch.jpg
 

Thread Starter

rsaumure

Joined Dec 29, 2019
4
Ok so if the voltage across the open switch is around .5 volts, I need to figure out how to get that up over 1 volt for the switch to work - correct? Do you know if there are any values of resistors that could be changed to increase the voltage? So for example, if I were to cut the value of R2 in half - from 2.2M to 1M the voltage to SWA (switch) would roughly double? Then the piezo might work?
 

Thread Starter

rsaumure

Joined Dec 29, 2019
4
I have also found that by placing a small 22 micro farad electrolytic capacitor off the + swa in series with the piezo, allows the piezo to control the circuit. My thought is that the capacitor develops enough charge to operate the piezo. It not all that reliable as I usually have to hit the piezo a couple of times to get it to work. Maybe a larger capacitor? Any thoughts?
 
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