LDR

[lucas abela]

i really wanna make the mutron III but can't figure out what i need to buy for the LDR?

i know its some kind of optic sensor but am at a loss on what exactly i should be buying as searching LDR on smallbear or mammoth dosnt help

if anyone have give me a clue it'll be appreciated

[motterpaul]

I just built a compressor using these and it work great. The LDR I got is the GL5539 - it works great with 3mm LEDs (I used red).  It was actually much easier than I expected. I did try the same on with a 5mm and I think I burned it out (not sure).

All i did was put a bit of shrink wrap around both parts and laid the LDR against the LED - it does not have to be in complete darkness, but you get more out of it when it is mostly covered.

[nocentelli]

http://www.diystompboxes.com/smfforum/index.php?topic=95269.0

This is a fairly highly engineered solution, but you basically need two LDRs fixed together with both facing an LED. I don't know how critical the LDRs' light/dark values are, but you should probably pick up a few pairs of LDRs to try out and rig up a temporary way of mounting them as in the link; I imagine you could just punch the legs of the pair of LDRs through a small bit of polymer foam (e.g. the pink stuff you get ICs stuck to) so they sit very close, then do the same with the LED in another bit of foam and jam them facing each other in a light-proof tube, use blu tac or modelling clay/plasticine to hold them in place.

To hook it up, the LDRs connect the opamp filter stages in parallel with 220k resistors, and this probably means the actual light and dark resistances are not terribly critical since they just need to sweep from "high" (in the megohms) to "low" (in the low kilohms): it is likely more important that the LDRs sweep the same range in a similar fashion, hence buying and testing pairs.

A simpler solution is to use two separate single LDR||LED vactrols like madbean's nautilus (updated mutron III) or the lovetone meatball (9v mutron III with a  dozen controls) but you'll still get more funk with matched LDRs lit by identical LEDs.
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[kirshman]

I used this one from tayda:

http://www.taydaelectronics.com/photo-conductive-cell-resistor-ldr-650nm-radial-ke-10720.html

with this led:

http://www.taydaelectronics.com/leds/round-leds/3mm-leds/led-3mm-orange.html

for the add on board for the deprofundis delay. I also used heat shrink around it and it works like a champ.  

[motterpaul]

I actually found it was not that complicated at all. As long as my LDR was in proximity of the LED it worked, even with just a couple layers of masking tape over them. They don't have to be touching, in fact in the end I think I left about 2-3 mm between LDR and LED and I get more gain than I need (It breaks up when dialed up to full on). But as that indicates, the circuits I built include pots to turn up/down the brightness scale of the LEDs, so you can really adjust the LEDs to glow as much or as little as you need them.

For example - with a compressor you adjust the amount of compression by adjusting the brightness scale of the LED. If it is a mutron and it needs to be in a specific range, I think a trimpot would be the answer to helping you dial it in (and I seem to recall talk of a trimpot in that circuit)

By the way - it is very easy to take an LDR and hook up a voltmeter and just see how it reacts to light.

My LED & LDR are just sitting in an unsealed tube of heatsink (I didn't close it off, I just pushed it on over the LDR and the LED, then pushed them down to face each other and flattened out the heat sink tube), which means some light gets in the ends - but it doesn't matter, because the small amount of ambient light doesn't compare to the brightness of the LEDs.