I'm a beginner with EE and trying to find the peak amplitude of an electric guitar signal (0-300mV) using an Arduino's 0-5v ADC. I'm going to use the data to pulse lights in accordance with each strum of the guitar.
I've figured out so far that I need to use op-amps to:
- Rectify the 0-300mv AC signal (full or half wave)
- Amplify the signal to 0-5v
- Use a voltage peak finder to locate the peak
- Use a buffer to protect against impedance (not sure if I need this?)
I've found circuits that use op-amps to do all of these, and they work fine, however they are all independent of each other.
My Question: is how do I combine all of these together into one circuit and how many op-amps should I really need. My approach initially was just to daisy chain everything, but I'm not sure that's the correct approach. Also, most of these use a buffer op-amp as the last step, do I really need one if I'm sending the signal into an ADC?
Best Answer
I think you can do all of this with just two op-amps (although someone will probably correct me).
The first stage is the peak detector and decay. The op-amp is wired to emulate a perfect diode. We take the feedback signal from after the diode so that the op-amp drives hard enough to overcome the voltage drop of the diode. Being a peak detector, it doesn't really eed a rectified signal. The capacitor holds the peak value, while the resistor decays it. You can make the decay slower by choosing a larger capacitor and resistor. And vice versa.
The second stage is simply 15x gain. It has low output impedance.