"Signal" LED

[Seven64]

So I have experienced quite a few pedals that have a sort of "signal" led that illuminates whenever the circuit is passing the guitar signal.  I know this is easily attainable with the clipping section of a dirt pedal.  I was wondering if there was a simple way to add this to any circuit, or a simple circuit that only does this...... 

I think it would be a neat feature to add to a few of my builds.........

[mth5044]

Check out the first section of the Clari(not) schematic posted by Doug Deeper in this thread:

http://www.diystompboxes.com/smfforum/index.php?topic=74294.0

The LM386 and everything around it is used to light the LED which interacts with the LDR in the circuit and is responsive to guitar signal. You could take that LED and all the circuity up to C4 and use it. Tack on whatever circuit you want at the R5/pin14 junction and it should work.

[deadastronaut]

here ya go.

http://www.aronnelson.com/gallery/main.php/v/chickpea/sound2light2.jpg.html

386.  it  needs a minimum of 2 leds if i recall....someone said it may cause noise in the effect used with it ..

so breadboard it to try out.  but works as a 'signal' for sure..

[samhay]

For a slightly different approach, take a look at any of the optical compressors/limiters. The signal has to turn an LED on somehow...

[induction]

This should work:


Attach whatever you want to monitor to the point marked 'signal'.  Adjust as necessary for more (increase R2) or less (decrease R2) sensitivity.  Any op-amp should work fine, and there should be no noticeable effect on the sound.

You can remove one of the leds if you prefer.  Then you will only see either the positive or negative voltage swing of the signal instead of both.

[Gurner]

Attach whatever you want to monitor to the point marked 'signal'.  Adjust as necessary for more (increase R2) or less (decrease R2) sensitivity.  Any op-amp should work fine, and there should be no noticeable effect on the sound.

If you feed in a raw unbuffered guitar signal...it will most definitely colour the sound (the input impedance of your cct is way too low)

Also those LEDs are completely DC biased 'off' with no AC signal, which means they won't light until the AC signal gets up close to the fwd voltage of the LEDs. So, if blue LEDs, that's 3.3V (or 6.6V peak to peak AC signal needed). In short, you'll need a fair amount of gain to get those LEDs to light up ....not helped by R5 being way too high - assuming the AC signal can get to 7.5V peak to peak on the output of U1, then that's 3.75V peak ...minus the forward voltage of the led ie blue led  3.3V, means 0.45V being dropped across R5, so the LED current  is 0.45V/R5 = 0.45mA ...it's going to be a damp squib at that amount of drive!)

[induction]

You're right. How's this?



Again, sensitivity can be adjusted via R2.  If you use red leds (Vf around 2V), would this work?

[induction]

sorry double post.

[Gurner]

no that's not right at all...you're biasing up the wrong opamp pin (you need to bias the +ve pin)

[induction]

One last try:



Any good?

[Gurner]

almost...you need a dc blocking cap between R1 & ground.

[induction]

Ok.



Thanks for your help Gurner.

[artifus]

[Seven64]

here ya go.

http://www.aronnelson.com/gallery/main.php/v/chickpea/sound2light2.jpg.html

386.  it  needs a minimum of 2 leds if i recall....someone said it may cause noise in the effect used with it ..

so breadboard it to try out.  but works as a 'signal' for sure..

threw this on the breadboard, but couldn't get it working.  do i need a 386, or would any op amp work?

[puretube]

here ya go.

http://www.aronnelson.com/gallery/main.php/v/chickpea/sound2light2.jpg.html

386.  it  needs a minimum of 2 leds if i recall....someone said it may cause noise in the effect used with it ..

so breadboard it to try out.  but works as a 'signal' for sure..

threw this on the breadboard, but couldn't get it working.  do i need a 386, or would any op amp work?

LM386 is NOT an opamp, but rather a power-amp...

[puretube]

here`s an even simpler one...
(no LED however, but rather a "bulb"-indicator)

(7052 is a power-amp, too!)

[deadastronaut]

@seven: yes it has to be a 386.amp....not opamp.

[Gurner]

here`s an even simpler one...
(no LED however, but rather a "bulb"-indicator)

(7052 is a power-amp, too!)

the TDA7052's input impedance @20k, is way too low to feed in a standard guitar signal....your one component circuit needs more components!  

[deadastronaut]

right who can make the ''smallest led indicator from a guitar signal competition''..

the winner gets to see an led light up..

and a fortnight for 2 in the dark.

[puretube]

the TDA7052's input impedance @20k...

100k, see p.5
(what a diff`rence an "A" makes...)

...is way too low to feed in a standard guitar signal....your one component circuit needs more components!  

obviously not, as the vid proofs...
[actually, for the video there indeed was a third component installed in series with the bulb:
a speaker-cabinet (left jack), whose sound can even be heard in the background... see following detailed pic:]
(right jack: guitar)


7052 gain: ~40dB - enough to get 10V out from 100mV in
(like used in all those "Slicing Bread"-circuits...