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Topic: Power IR LEDs + 9V battery + eye safety = possible ? (Read 677 times) previous topic - next topic

amundsen

My current project includes a circuit with 3 940nm IR LEDs to be put on a glove. The LEDs are in series with a resistor and they are powered by a 9V battery. The LEDs are tracked by a Wii remote IR camera. It's important for the project to have 3 LEDs because they make a shape used for position and angle tracking.

However the beam width of those 3mm IR leds is too narrow (< 60 degrees) and the tracking fails as soon as the hand slopes even just a bit. Therefore I have bought 1W high power LEDs because they have a beam of 120 degrees. Now my concern is to provide enough power to the LEDs but simultaneously limit the light emission to keep the device safe for the eyes and save battery power.

The question is: can I reach these goals simultaneously with a 9V battery and a simple resistor (possibly by "underpowering" the LEDs) or should I change my circuit ? Would a PWM-powered circuit be necessary and in this case would a microcontroller be mandatory (a Lillypad maybe ?) ?

Thank you in advance for any advice or schematics.

CrossRoads

Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
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amundsen

I don't have complete ones (cheap buy on eBay). However I have tested the component and the forward voltage seems to be around 1.09 V. Using a 9V battery and a variable resistor I have measured the lowest possible resistance necessary (around 250 ohms) to have some light (estimation with a webcam). So I don't think safety is a concern anymore. I have lowered the resistance down to 120 ohms with 3 LEDS in series. The circuit is not heating but the current seems to drop quite fast. I don't know if this could be a multimeter issue but the current falled from 75 mA to less than 30 mA in a few minutes. At that point I switched the circuit off to spare the battery. So I am still wondering if I could have a better powering circuit because I am afraid to empty the battery quite fast (even if the one I have been using for the test wasn't full and was giving 7.6 V rather than 9 V at start).

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