My friend and I were tossing around idea's for a project. I myself play guitar and have previously studied the electrical properties of the instrument. After some testing, we determined that the AC rms output voltage ranged from 50 mV to about 400 mV, depending on which chord or note i played (various frequencies and how much you disturb the magnetic field around the pickups). My question is; how can we convert this ac signal to a dc signal, that will be used to charge a cellphone? We considered using a simple rectification circuit with a voltage regulator, but now we are considering a voltage amplifier then a rectification circuit? I guess we are not sure on how to tackle a project like this, if it is even possible. Any input is appreciated!

 

Welcome to AAC!
There are a few snags :-
1) There is very little energy in a twanged string, so it would take months to charge a battery,
2) If you extracted much energy from the string it would severely damp the vibration, so you'd have weak sound.
3) Rectification of such low-level signals would be very inefficient, since it takes about 300mV to get even a Schottky diode to conduct significantly.

 

My friend and I were tossing around idea's for a project. I myself play guitar and have previously studied the electrical properties of the instrument. After some testing, we determined that the AC rms output voltage ranged from 50 mV to about 400 mV, depending on which chord or note i played (various frequencies and how much you disturb the magnetic field around the pickups). My question is; how can we convert this ac signal to a dc signal, that will be used to charge a cellphone? We considered using a simple rectification circuit with a voltage regulator, but now we are considering a voltage amplifier then a rectification circuit? I guess we are not sure on how to tackle a project like this, if it is even possible. Any input is appreciated!

There's not many diodes around that wouldn't lose 400mV in their Vf.

 

You could feed the guitar pickup output through a transformer to increase the voltage but this will also reduce the current available. This would make rectification practicable. The energy available is going to be very low so charging a battery is going to take a loooong time.

 

You could feed the guitar pickup output through a transformer to increase the voltage

May not be practical. It would presumably need a custom-built transformer, since a guitar pickup typically has a DC resistance of ~6k and an inductance ~ 1.5H.

 

When I hammer a power chord on my Les Paul I can get 6 volts peak to peak so rectification is not a problem. The real problem is the several K of resistance in the pickup which makes the energy resemble 3 milliwatts. At that rate, it would take 325 hours to charge a AA nicad battery.

 

When I hammer a power chord on my Les Paul I can get 6 volts peak to peak so rectification is not a problem. The real problem is the several K of resistance in the pickup which makes the energy resemble 3 milliwatts. At that rate, it would take 325 hours to charge a AA nicad battery.

IOW: it ain't gonna be anywhere near 6V with even a whiff of a load on it.

It'll probably take the battery's shelf life to charge a phone battery - everyone has said as much in some way shape or form.