I don't know what you would call this circuit, but it's designed to turn a piezo signal into a ON/OFF signal. This is for a kick drumpad.

I'm fairly sure I have it built correctly according to the diagram and real world tests confirm it's functionality as perfect, but since I don't fully understand it I'm not sure if it's supposed to be inverting the output or not. I would tend to think it shouldn't.

Best I can do to replicate the piezo source is use an AC source.

R1 -used to control main pad sensitivity.
R4 - used to adjust kick pulse duration. Also used to control with rebound hits, so multiple hits aren't registered from a single kick.

Attached is my circuit with scope, and the original circuit.

Can anyone see why this would invert the output? and why the op-amp seems to turn the AC signal into a square wave? (I think it's supposed to)

 

Hello,

in the first diagram you use the op-amp as a non-inverting amplifier with open loop amplification. So you get a square wave output.

The second diagram shows the op-amp as inverting amp with close loop amplification. The amplification can adjust with R1.

I think that's the mainreason of the invert output.

Best regards

Rainer

PS: Sorry, if my English is not so good.

 

The 555 Projects

555 Schmitt Trigger

 

The LM386 is an an audio amp, NOT an operational amplifier.

You need to use an opamp whos' common mode input range includes ground.

As noted, you have swapped the inverting and noninverting inputs - but you can't simply use an audio power amp instead of an opamp. They are different critters.

Also, you cannot use a TL07x, TL08x nor LM35x family opamp, as they cannot "see" within 3v of the negative rail.

 

Hello,

in the first diagram you use the op-amp as a non-inverting amplifier with open loop amplification. So you get a square wave output.

The second diagram shows the op-amp as inverting amp with close loop amplification. The amplification can adjust with R1.

I think that's the mainreason of the invert output.

Best regards

Rainer

PS: Sorry, if my English is not so good.

I'm not sure what you mean by open/close loop. What's different on my circuit from the diagram?

I see I had the wrong pins on the op-amp connected.

 

The LM386 is an an audio amp, NOT an operational amplifier.

You need to use an opamp whos' common mode input range includes ground.

As noted, you have swapped the inverting and noninverting inputs - but you can't simply use an audio power amp instead of an opamp. They are different critters.

Also, you cannot use a TL07x, TL08x nor LM35x family opamp, as they cannot "see" within 3v of the negative rail.

Thanks for pointing that out. I was luckily able to find a SPICE model and create the component in multisim for simulation.

I think it's working the way it's supposed to. I get convergence errors in simulations, but that could be any number of ridiculous things.