I have a design project for my electrical engineering class where I'm designing a signal tracer akin to Tripplett's Fox and Hound series.
For a reference, I tested the output of a commercial tone generator to see what kind of signal I'd need to generate for it to be received by the handset and found a 40 VPP square wave(well above the 3V from the batteries) so I assumed there must be a transformer. I opened the case and identified a tiny little transformer, about a 1 cm cube.
I tested my own generator with a standard power transformer with a 1:10 ratio and it worked fine, but it's rather bulky for something that could be much smaller. Unfortunately, I'm not sure what I should be searching for.
SMPS transformers all appear to be rated for 40khz or more, and I'm only outputting 2khz. Is it just a custom wound thing? If not, what should I be looking for on digikey/mouser?
The picture isn't very good, but it only has 2 leads per winding, no taps.
I'm using 9v rather than 3v input, so I need about a 1:5 ratio…
Best Answer
As a first pass, I'd say you are probably looking for an "audio transformer".
Update: I'm a bit concerned whether you're fully aware of the type of signal you need. Is this intended to test phone wiring? If so you might want to read this:
http://www.epanorama.net/circuits/teleinterface.html
I don't think you need 40V signals for them to be audible in a phone handset. Indeed, I recall connecting them via 1:1 transformer to record them on a tape recorder, which suggests signals in the 1V range.