So I graduate on Saturday. I will be in a sea of other graduates making it difficult for my family to find me. My thought was to wire up a single IR LED to my cap (as inconspicuous as possible of course). The idea is that they will be able to scan the crowd of graduates with their camcorder and spot my cap through the viewfinder. Since it won’t be visible to the naked eye no one else would really know about it. I leave this on while I walk into the arena giving them ample time to find me and then turn it off before having my picture taken receiving my diploma.
There’s one problem. I don’t know a whole heck of a lot about electronics, resistors, capacitors, diodes, etc. Well I do know that I won’t need a capacitor in this simple circuit but that’s about it. Since Radio Shack associates are about as useless as it gets when it comes to the electronics they sell, I am calling on you guys to help me with this project. I figure I’ll need a small watch battery, some wire, an IR LED, and maybe a resistor or two. Which ones is completely beyond me. I’m sure someone out there could wire this up in their sleep. If you could take a few minutes and point me in the right direction I would greatly appreciate it! Thanks in advance!
Why not just palm a television remote control and shine it in the general direction of your folks. An LED will be very directional and if you don’t have your head turned just right, they probably won’t be able to pick it up.
The specifications of high power IR LEDs are sufficiently similar to high power visible red LEDs that you should just be able to get one of those little LED keychain lights - a red one (not blue or white or anything, as they operate at a higher voltage) - replace the red LED with an IR one (make sure you install it the right way around) and you should be good to go. It might not be the ideally-engineered solution, but it will work for the few minutes you need it, at least.
If you’re buying the IR LED from Radio Shack or similar, it should come with the specs, including operating voltage and current. You need to select a battery (or a series of batteries) whose output voltage is higher than the LED’s operating voltage, then use a resistor to drop the voltage. Voltage drop across the resistor is I*R, where I is the LED’s operating current and R is the resistance.
So for example, if you have a 1.2V 30mA LED, you can use one 1.5-volt battery and use a resistor to drop 0.3V. The resistance you need is R=V/I=0.3V/0.30mA=10 ohm.
Well I don’t have too much to do between now and then so I may take a spin by Radio Shack, but I really think Mangetout’s idea would be best. And while cleaning I actually found one of those cheap keychains. Thanks for the advice all!