I was trying to amplify the signal of a piezo, which is very low and amplify it so that I could use it to latch a flipflop. I had the LM358 opamp so I made a differential amplifier by a gain of 50 so that the output would reach 5 volts which is a high logic level.
I got the design of it from internet, I just changed the gain.
I was measuring the output with my multimeter (I do not own an osciloscope,) but the output was never what was expected. The maximum voltage I measured was 1volt, but it should have been 5volts.
No matter what I tried, the output was same.
I do not know if the opamp is not working or if I am measuring wrong.
Please tell me what am I doing wrong or what the problem is.
Best Answer
Aside from obvious questions as to whether your piezo is the same as whatever some random site on the internet might have used, and whether yours is being hit as hard, there is really no way to measure the output signal with a multimeter. The pulse will be brief.
If you are seeing 1V on a multimeter it may well be railing at +3-4V (the most the op-amp can manage, assuming a +5V supply- you don't specify) briefly. Try it on the flip-flop.