LED input/peak/VU meter

[mdame]

I was wondering how to wire an indicator LED to flash with the signal from the guitar.  The Diamond Compressor does this with a 2 color LED, as well as many preamps I have used.  I think that would be best, that way one color is on all the time and flash the other color.

[mdame]

Help! 

FSB has an unverified schematic for the Diamond Comp, and the LED section looks like it would work, but I dont really understand which parts are dedicated to the LED circuit and how to use it on other circuits.

[jasperoosthoek]

Link please?

[mdame]

Certainly.

http://www.freestompboxes.org/viewtopic.php?f=7&t=850&p=135805&hilit=diamond+compressor#p135805

[jasperoosthoek]

  That link doesn't look right.

[mdame]

http://www.freestompboxes.org/download/file.php?avatar=23677_1299733782.jpg

[mdame]

It wont allow me to link to free stompboxes.  replace the dots.  sorry for the inconvenience.

[artifus]

http://www.diystompboxes.com/smfforum/index.php?topic=82843.0

http://www.geofex.com/Article_Folders/ECFtech/ecftech.htm

[jasperoosthoek]

It wont allow me to link to free stompboxes.  replace the dots.  sorry for the inconvenience.

I'm writing this on my smart phone... I'll check it tomorrow.

[mdame]

The flashing LED is ok, but I am looking for the color change so that there will be an LED on when the effect is on, regardless of playing.  I will read the envelope control article and go from there.

[mdame]

http://s1185.photobucket.com/albums/z352/mdame87/?action=view&current=DICOMPREV2.png

UNVERIFIED

[jasperoosthoek]

This part takes care of the red led:


You could try something like this:


The green will go off when the red starts to burn. So without sound it will be green and then if you apply a signal it will go from yellow to red (green and red light combined is yellow).

Just breadboard it and see if it works or needs any tweaks.

Good luck!

[mdame]

Thanks! mainly i was unsure if i should include Q8 and where to put it in a different circuit.  I am guessing you connect the base of Q8 after a couple gain stages to prevent signal loss?

[jasperoosthoek]

Yeah, that would be a good idea. Yesterday after posting this I realized that the normal guitar signal is not loud enough to do anything. You will a gain stage anyway.

Q8 is just a unity gain buffer. But Q7 will only start to conduct when part of the signal exceeds the base-emitter voltage of about 0.5 to 0.6 volts, hence the larger signal needed. My guess is also that there has to be a resistor in series with C27. Right now the emitter of Q8 directly loads the base of Q7. That seems a bit awkward to me. If you breadboard it you could place a 1k or less resistor in series with C27. This is an unverified schematic so you never know if it would be there in the original circuit.

[mdame]

Any idea where to get the LED?  can only find green/yellow.

[jasperoosthoek]

I bought one at my local electronics shop, no idea where they got it from. Radioshack has one: http://www.radioshack.com/product/index.jsp?productId=2062549 But the picture shows an LED with two leads...

They can be found on ebay too: http://cgi.ebay.com/10-x-3mm-Bi-colour-Diffused-LED-Bi-red-yellow-green-/260736448784?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item3cb51a7910