IR LED to dim...

gamer88

Me and my partner are trying to increase the voltage to the ir LED's. The robot we are working on is a SumoBot(prob &#8482[noparse];)[/noparse]. It has basic stamp 2 on it. We have tried everything, and short of hooking it straight up to a battery (which the recievers don't pick up) we cant get it to work! HELP PLZ

kwinn

You can not hook a led directly to a battery. There must be some form of current limiting or you will destroy the led.

gamer88

That was not my plan for this robot. I am just looking for a way to make the IR LED brighter on this robot so it can detect further.

Mike Green

The brightness of any LED depends on the amount of current through it. Most ordinary LEDs, including most IR LEDs can handle up to about 20 milliAmperes. The Sumobot's IR headlights use a 220 Ohm resistor to limit the amount of current to the LED to about 15mA. Theoretically, you could change the 220 Ohm resistor to a 180 Ohm or 150 Ohm resistor and get a bit more current (and brightness), but the 220 Ohm resistors are built into the Sumobot board and would be difficult to replace.

1) It's not simple to increase the IR detection distance. There are all sorts of ways to try, but a lot of them won't work with the Sumobot because of the way it has things built-in. Just making the IR LEDs brighter won't necessarily work because you'll have more reflections and the area lit by the LEDs may broaden. Think about using a flashlight to light up a dim room. As you brighten the flashlight beam, more things may show up to the side of the beam. The detector may falsely trigger on those.

2) If you tried connecting an IR LED directly to a battery, you've probably destroyed it. It doesn't take long for the internal wires in the LED to melt when too much current is applied.

Say more about what you want to do with the distance detection ability.

gamer88

ok, thank you for that incite. The sumobot does have a board on top that i can use to alter the resistance of a IR light. Also, do you know of anyway that i could increase the distance if you can fully alter the IR and detector?

Mike Green

Probably what I'd do would be to make a kind of IR flashlight using 4 to 6 IR LEDs in a cylindrical sort of configuration, each with its own 180 Ohm resistor, with the LED cathodes connected to the resistors, the other end of the resistors all connected together and all the anodes (the long leads) all connected together. I'd use a switching transistor like a 2N2222A which you can get from RadioShack with the collector connected to the parallel resistors, the emitter to ground, and the base connected to where the LED originally plugged into the Sumobot (where the built-in 220 Ohm resistor is connected). The parallel LED anodes would be connected to +5V. The result would be a very bright IR light source modulated at around 38KHz using the FREQOUT statement.

There's nothing really that you can do to improve the IR detector unless you have a lot more experience with electronics than you seem to have. You could make a "hood" for the detector to narrow the area that it "sees". I've used a spare black plastic tube like the one used over the LEDs. You can cut off the extra bits so it fits over the "bulge" on the front of the detector, then fasten it with a tiny bit of glue so the glue doesn't block the "view".

Post Edited (Mike Green) : 1/9/2010 2:48:59 AM GMT

gamer88

Ok, thank you. I deal in computers more than electronics, went into this competition being able to program. My partner is the one that is good at electronics.