I recently had to get rid of my rarely-used oscilloscope due to space restrictions and started looking at alternatives. The handheld devices started from about $70, but had known of some PC kits.

I thought, couldn’t I just use the input for my PC sound card? So came across the Poor Man’s Oscilloscope. I also knew of $300 iPad oscilloscope, which was crazy money.

Sat lonely in my box of old electronics, however, was a upgrade-made-redundant Android device. A brainwave hit and I set about making my $0 oscilloscope. Here’s a video explaining it:

How to Build

The probe is a very simple modified mic and headphone set with a potential divider and some crocodile clips. You will need:

  • Android phone with OsciPrime Oscilloscope Legacy
  • 4 pole 3.5mm jack (e.g. a handsfree set that comes with a phone)
  • 2 resistors in a ratio of roughly 1:10
  • Probes (I used crocodile clips) with some cable (multicore is best)
  • Perfboard (optional – you could solder directly)
  • Heat-shrink / insulation tape

Below is a diagram of how to wire. The potential divider simply reduces the voltage in to the device, lowering the risk of killing the mic-in circuit in the phone.

The circuit is very basic and you could make it all in under an hour, but it’s certainly not fool proof. A more complex alternative using op amps can be found on this Instructable.

You may also run in to the problem of the headphone wire being annoyingly coated. I simply burnt these with a butane lighter, but you can read more on the technique here.

If you also build one, would be great to hear how you get on.