Injecting a test signal?

[bill0287]

What are some creative waves to inject a test signal into a pedal circuit (like on a breadboard)?

I could wire up an input jack and use a guitar, but I want something hand's free.  I don't have a signal generator, and I am looking for something to use on the bench. Basic sign wave is fine.

What other ideas do you have for injecting a signal?

[Kipper4]

I built a signal generator from RG Keen.
To be fair though I used guitar for testing most of the time. Maybe they're a signal generator app for this these days.
Have fun.
Rich

[FSFX]

A lot of guys just use an app on their phones or use a looper pedal with a rift recorded on it.

Otherwise you can pick up a simple oscillator kit on the usual online sites for just a few bucks.

[ElectricDruid]

Yeah, a 555 oscillator, maybe? You can get a square/pulse thing out of it, and a triangle-ish (shark's fin) waveform out of it, which are pretty good for testing, and provide plenty of harmonic content for checking tone controls are working and such like.

Put a simple 555 astable together on a bit of stripboard/protoboard and then add a couple of croc clips on wires so you can patch it in where you need it.

There are more complicated things out there, and some are pretty cool, like this:

https://www.madbeanpedals.com/forum/index.php?topic=31418.0

[GibsonGM]

I use R.G.'s "quick and dirty sine wave oscillator" too.  I just jumper it to the area I'm testing...an input cap etc., move it where I want it.

I like the pen idea! That's very cool.   Alternatively, one could make a probe out of an old pen an use that to inject signal - I did that with an audio probe using stranded wire I tinned and 2 part epoxy to fill the pen casing.

Hadn't considered using phone audio out for this, that def. has potential too. 

[ElectricDruid]

Another possibility that I tried was to buy a cheap MP3 player off eBay for $5 or something, and then put some guitar sound files on it. The microSD card for the damn thing cost more than the device itself! It has a standard 3.5mm headphone output, so I wired up a cable to go to a mono 1/4" jack, and then it's not bad as a test signal generator. The buttons are too small and fiddly is my biggest complaint - I should re-box it into a larger case with decent buttons and then it would see more use.

[Yazoo]

I have used Dick Cappels' 1Khz sine wave generator for years now and it has stood me in good stead. It is much easier to have a constant test signal fed into the circuit than having to manage a guitar at the same time. You can then trace the signal through the circuit, ideally with an oscilloscope. Dick was kind enough to reply to my email all those years ago, so thanks for your help Dick.