Electronics

Op-Amp's

These are analogue devices that can be used to amplify a signal or buffer it, or to compare it to a reference value. LM358 is an example of a dual-channel opamp.

When hooked up as a comparator you put the reference signal in to the - input (Inverting input), the + input (Non-inverting input) is for the signal. When the + is greater than the - the output goes to the high rail, otherwise it will be at the low rail. It's also really important to have a feedback loop from output back into the signal through a large resistor. The key word to lookup for details is 'hysteresis'. Introduction to op-amps.