Working late one evening trying to build a time-lapse trigger for my camera, I realised i had no optocouplers in my parts bin. My electronic store was closed for the night, so what to do?

Being the ingenious ex roadie that I am (in my opinion, you can fix just about anything with a ratchet strap and gaffer tape), I thought about how an optocoupler works. Basically it is an infrared led that shines onto an infrared sensitive transistor.

Hmmm I think. How about a light dependent resistor with an led? Sounds like a plan!!!

(Technically, this isn't an optocoupler, but it 'optically separates one circuit from the other', so it's good enough for me... at least 'till the shop opens.)

Step 1: Parts You'll Need

LED
I used an ultrabright white led that i had bought as a job lot for another project that didn't get off the ground yet (30 quid for 1000. Bargain!).

LIGHT DEPENDENT RESISTOR
I used one that i had in the parts bin (less than a quid)

HEAT SHRINK SLEEVE
I've got a box of the stuff that i picked up from the army surplus store.

Step 2: First Some Safety Precautions.

To stop any shorts, cover the anode and cathode of the led with heat shrink, and also the legs of your l.d.r.

Step 3: Time for a Face Off!

Place the led and the l.d.r. face to face and cover the two with some more heat shrink.

Step 4: All Done!

You now have a rudimentary optocoupler. The resistance in the l.d.r. is high when there is no current to the led. when the led is lit, the resistance of the l.d.r. drops and allows current to flow.

This is my first instructable, but hopefully I'll get a few more posted in the near future.