I need some direction....

[digi2t]

Hi folks,

Just need some direction here. I'm feeling dyslexic this morning, and my searches are coming up empty. I'm looking for a circuit that will;

- Detect a guitar signal input, and
- I can then use that signal to trigger a small 5v relay.

I'm thinking about the front end of the Mutron, with an adjustable gain, so as I can control at which point the switching kicks in, but I'm at a loss for the second part. I can't seem to formulate the right search keywords this morning, and I'm going in circles.

Actually, if I could control the trigger point, and the sustain (length of time that the relay would be active on the decay), that would be sweet. I think I'm into compressor territory here.

Any pointers would be appreciated. It's getting close to Halloween, and the mad scientist in me is boiling over.

[Gus]

google things like "sound activated light diy"  That got some hits

[R.G.]

Amplify the signal a bit, perhaps a lot. You're just trying to make a signal that goes all the way between nearly-ground and nearly V+. AC couple that to the input of a comparator. Set up the comparator with some hysteresis, perhaps a volt or two, but adjustable.

The incoming signal makes + and - going edges. The edges are coupled through the cap to the comparator as spikes or full signal, depending on frequency. The comparator makes square waves if the signal is bigger than the hysteresis amount.

Now trigger a *re-triggerable* one shot from the output of the comparator. The comparator senses signal and makes edges, perhaps one per zero crossing, until the signal drops below it's hysteresis level. The one shot output goes active on the first edge it gets from the comparator, and stays active until it quits getting edges, plus one one-shot timeout.

The trick in getting this to work well is to adjust the incoming gain and comparator hysteresis so you don't get edges all the time and leave the one-shot on all the time.

It's a variation of a missing-pulse detector.

[digi2t]

Thank you gentlemen. It was truly my lack of the right words/phrase that was messing me up this morning. That, and a lack of caffeine. 

I'm on track now. 

[UKToecutter]

Dino,

I used to have a circuit many years ago for doing something like this.
signal driving a transistor which in turn lit a grain of rice bulb coupled to an LDR.

Can't find it though.....   

[digi2t]

Dino,

I used to have a circuit many years ago for doing something like this.
signal driving a transistor which in turn lit a grain of rice bulb coupled to an LDR.

Can't find it though.....   

Welcome to my nightmare my friend.