phexagon

Hi, totally new to electronics.

I have am making a simple game controller mod soldering connections from a pcb to buttons. For example: http://imagehost.vendio.com/a/795303...oe_Inside2.jpg

However, I want add superbright led's/el wire to light up on button presses. These will be powered by 4AA batteries. They have to be on a seperate circuit (electronically isolated from the pcb circuit).

I know an optocoupler is an IC that couples two sides of the electrical world by a light beam, this way they avoid all chances of data or signal accident/interference.

Is there a cheaper alternative IC to an optocoupler that can do this (considering bulk)? I would like to know if a more expensive option exists too btw.

If there is no other solution can you tell me which optocouler would be best suited. I'm guessing a low current 4-pin optocoupler? Will a 6-pin work aswell (they seem more common and cheaper)? Also which resistor do you reccomend so that it doesn't short? http://www.maplin.co.uk/Search.aspx?...source=15&SD=Y

cesco

Hi, I'm not a big expert in the field, but I made an "analog" optoisolator at a hardware hacking lab and it worked quite well. I think it is one of the cheapest solution for your problem.
You simply need a photoresistor, or light-dependent resistor, such as these

and a Light Emitting Diode, or LED, such as these
.

The photoresistor is a resistor whose resistance depends on the amount of light to which it is exposed. Then, if you tape together a led from a circuit and a photoresistor from another circuit, with electrical tape, when the led is on the resistance will go down, and vice versa. You can then use your signal to light up the LED, which makes the resistance go down, "closing" the other circuit.

This probably isn't the perfect solution, because you still have a big resistor and not an open circuit when the light is off, but it's cheap (less than 1$) and manages to keep the two circuits completely separate.

jpanhalt

Have you discovered the product selection engines many vendors have? I use Digikey. If the question is bulk, the 2.5X2.5 mm (BGA) is about as small as I found. Is that still too big?

The selection engines also let you define number of circuits, current, etc.

Here's just one of many examples: http://www.fairchildsemi.com/ds/FO/FODB100.pdf

John

Hero999

How many opto-couplers do you want?

You can buy 16 pin DIPs with four in one package which will work out cheaper than buying four, four pin devices.

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phexagon

Thank you, I already considered this option, but I found out that (as you said) it is not really an open circuit when the light is off. I experimented with the led off in total darkness and there was still a dim light on the led! This would waste battery consumption. Maybe I was doing something wrong. I was considering this as the cheapest, most straightforward solution.

oh thx jpanhalt, that is a good idea. And that example is great.

Oh, I will look into the 16-pin four in one packages. This one looks interesting http://dspace.dial.pipex.com/isocom/isq202.htm