Thursday, November 18, 2010

Current Regulator Circuit

Yippee! I successfully remembered my training as an electrical engineering student, and built a current regulating circuit to guarantee constant illumination from an LED under varying supply voltages.

(application: RC car headlights)

I won't bore you with a circuit schematic ;-) but it involves two LEDs each having a Vf of 2.0 V and an If of 20ma, a 75 ohm resistor, and a 10k resistor (though it probably oughta be 1k). The resistor values need to be adjusted for the Vbe of the 2n3904 transistor (~0.75 V under these conditions), but the goal is to guarantee 20ma through the LED on the top, for a Vs of 4 to 6V.

Saturday, November 13, 2010

Quick Drying Random Things

Ever need something dried quickly, but can't microwave it, stick it in the oven, or put it in the clothes dryer? Try this!

Just tape a hair dryer into the opening of a PAPER grocery bag, put the thing to dry inside, and partially tape it shut. Turn on the hair dryer, and wait a couple of minutes. Whala!!