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Originally Posted by Dave Flowerday
Everyone,
While assembling our IR beacons we discovered that the "First Infrared Beacon" assembly sheet that was included in the kit is incorrect. The connections to pins 2 and 3 of the FET are reversed. FIRST has been notified, and I hope they'll release updated directions to address this. In the meantime, if you know your way around electronics you should be able to take care of this yourself (search for IRL3103 on Google if you'd like to look at the datasheet for the FET included with the kit). If you don't know exactly how to modify the circuit to be correct, I'd recommend that you just wait to assemble it until new directions are released.
For those interested, you can see where the error is by looking at the sheet included in the kit and examining the schematic that represents the internal "guts" of the FET and compare it to the schematic right at the top of the datasheet for the FET. You'll notice that the FIRST version has pin 3 connected to the "D" (for Drain) line of the FET, but if you look at the "Lead Assignments" on page 8 of that same datasheet that Drain is really pin 2.
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I've whipped-up a replacement schematic that can be found here:
http://kevin.org/frc. The data sheet for the IRL3103 is also there. For those interested in electrical engineering terminology, this type of circuit is called a "low-side switch" because is switches the ground or current return side of a load as opposed to a "high-side switch", which switches the power or current source.
-Kevin