Infrared signalling and range

[David Dorward]

I'm trying to use an IR LED to send signals to a receiver using an Arduino Pro Mini (3.3v/8Mhz) but I'm having some serious range problems (if I get the emitter close enough to touch the sensor then it will pick up the carrier wave some of the time).

I'm running the board off a single Li Ion CR2450 and am currently hooking up the LED directly to the Arduino. 

I can probably get a boost by using a MOSFET to channel power from the battery into the LED, but I suspect that still won't give me much output. 

I think the way forward involves capacitors, but Google has only managed to turn up some documents that are a little (or a lot in some cases) over my head. (I'm a software person and my electronics skills are very novice at present).

http://www.lirc.org/transmitters.html

http://www.lirc.org/improved_transmitter.html

http://www.robotroom.com/Infrared555.html

Am I on the right track with these? And can someone hold my hand through interpreting them?

Thanks.

[Adrian Godwin]

None of these will help much. They all assume there is a fairly high voltage available (from the RS232 driver) but that it doesn't have enough current available, so they charge a capacitor up and use it to generate a brief flash of higher intensity (sometimes using multiple LEDs).

Your problem is that you don't have much voltage available and some is lost in the arduino output. Trying to increase the current by reducing the series resistor (if you have one) doesn't help much as the increased current causes more voltage drop in the arduino.

You may be able to help by driving the LED with a transistor from the arduino pin. This can be capable of lower 'in' resistance, getting more of the battery voltage applied to the LED. If the pulses are short, you may be able to overdrive it a bit.

Some circuits use a capacitor in a more complex way. They charge off the battery, and then reconnect it in series, doubling the battery voltage. I can't find an example of this at the moment, but they do have the problem that they can't sustain the pulse for very long.

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