Sparkfun OpAmp Breakout LMV358
The LMV358/LMV324 are low voltage (2.7â5.5V) versions of the dual and quad op amps, LM358/LMV324, which currently operate at 5â30V. If you need to use a piezo as an analog sensor into the arduino, this is the chip and breakout board to use. Most OpAmp chips operate by looking at 2 voltages and amplifying the difference between them. Â The chip has a pot that lets you dial in the amplitude of that difference. One thing I noticed is that when I hit the piezo you get negative values. This can be fixed by using an absolute value function. This happens because in order to contain huge spikes in the voltage of a piezo(+30v), the breakout board uses a voltageÂ dividerÂ which manages that voltage and sets the output of the OpAmp at 2.5 volts. Tom and I used anÂ oscilloscopeÂ to verify this. This is important because the when you hit the piezo it spikes to +5 and to 0. This makes sure that we do not send too much positive voltage to the arduino and negative voltage which would fry it.