Smartphone Signal Generator

How to build a small amplifier for your smartphone signal generator

You can find plenty of signal generating software for both Android and iOS devices.

Here's an example of Audio Tool for iPhone and iPod Touch. They obviously range between 20Hz and 20KHz (human audible range) because audio output of these devices is meant for music:

However, the voltage ranges of operation are pretty low.

Building a small amplifier for your phone:

I started out from Amanda Ghassaei's Arduino Waveform Generator.

Since the function generation piece of her circuit will be entirely replaced by the iPhone, I just built the OpAmp piece as follows:

I used alternative parts to replace some of these suggested components, starting by the OpAmp, then following for the 22K instead of 20K resistor, and 25v capacitors instead of 50v. Feel free to use slightly different components. 

Prototype:

Building process: Note how the SMD chip levitates on top of the board. I chose pins for easy grabbing with alligator clips or scope hooks.

And the finished product:

The two contacts at the top are the power in connectors.
The other two at the bottom are the signal Out terminals for your part or your scope or both.
The signal is fed from the Smartphone via the cable at the side. The triple white wire goes to the potentiometer. 

Done!