Instructables

Polygraph re-purpose?

Okay, here was my idea: an old polygraph is basically an amplifier connected to a pen graph. pen graphs and amplifiers were used on the old oscillographs. Those were replaced with oscilloscopes, where the amplifier connects to the deflection coils on a CRT (or into an AD converter, then yadda yadda yadda.)
My thought was, because people with old polygraphs in my experience want to dump them, while people with an oscilloscope of the same capabilities want a premium for them.
One guy near where I live has an uncle who collected stuff, and he has an old Heathkit oscilloscope he'd like $75 for. Square tube, relatively massive body, very, very low bandwidth. He also wants about $50 for the old tube base done, with the round CRT display. And it won't show a trace when powered up.
But he has a somewhat dinged up polygraph with chart recorder that is for about $10.

Could I, perhaps with some modifications, turn that polygraph into what works as a low-bandwidth oscilloscope/oscillograph? The old tube based one would be of collection interest only, and being old and Heathkit, I doubt their accuracy. Is there any way the old polygraph could be turned into the world's least practical oscilloscope?

Kiteman2 years ago
For $10, it's worth a try. You could also try other inputs, such as sound or temperature.