Pedal problem

[Sahiru]

what is the "shrink tube" in http://www.freeinfosociety.com/
electronics/schemview.php?id=315 ?

thank you

[anchovie]

http://en.wikipedia.org/wiki/Heat-shrink_tubing

[Sahiru]

thank u. the idea is to give the ldr only the light emmitd from the l.e.d. is it?

[Mark Hammer]

Yes.  To some extent, once you put the LED and LDR inside a chassis, and close the lid, you have blocked off light.  But of course testing the unit, and adjusting it, before you close the lid, becomes almost impossible.  So, for the purposes of mimicking how the circuit would behave when the lid is closed, it is helpful to seal off the LED/LDR pair from all light sources. 

Heat shrink tubing is a good strategy for this.  It also keeps the LDR in a fixed physical relationship with the LED.  I will hasten to add, however, that the shrink tubing is NOT perfect.  Light can come in through the base of the LED (the side where the leads stick out of), so simply covering the plastic part of the LED is often not enough to get maximum LDR resistance.  I have never done so, but I imagine it might be a good idea to get some of that black nail polish that Goths like so much, and paint the base of the LED so that light is blocked.

[Sahiru]

thank you.
using nail paint is a great idea. I will share the results
:-D :-D

[duck_arse]

I've been playing with ldr/led of late on the breadboard. it nearly drove me crazy. led and ldr in a tube cut from a printer cable, nicley opaque. but the superbright led at the top lets in too much desk-lamp light (and it's hard to bb in the lights out). so I put a plastic film can over the top, nice and opaque. only, there is still light leakage, I finally tracked it down to the light reflecting off the white of the breadboard. it was enough to flood/flare the ldr.

so I built the whole thing in a film can with grey lid, only wires poking out. no leaks now.