Variable power supply

The KEEDOX digital voltage display

As mentioned previously, the digital display takes it power before the LM317 and samples the output of the voltage regulator after the last set of capacitors. My display has three wires, red, black and white, and came with no instructions, so I guessed that red sources to the supply voltage, black to ground and white connects to the output of the voltage regulator, and I appear to have guessed correctly. NOTE: The image of the display at Amazon has different colored wires.

I attached the display to the board by enlarging two of the existing holes (the mounting holes on the display closely matched the 2.54mm spacing of the perforated circuit board), using a pin vise and drill bit. I made plastic standoffs by sawing off segments of modeling sprue (from a 1/48 Hasegawa P-51D Mustang kit, to be precise) and boring out a hole. The screws came from my parts bins.

The potentiometer

The potentiometer I chose is large for ease of turning and travels 300°. It has three pins and one of the outer pins is connected to pin 1 of the LM317 (via R1) and the other outer pin is connected to ground. And the center pin must be connected to one of the outer pins for the potentiometer to work properly. It doesn’t which outer pin is connected to the center pin, but it will determine whether resistance increases or decreases as the shaft is turned clockwise and counter-clockwise. By the way, my pot lacks a knob because they cost a lot (in comparison to the price of a the potentiometer itself) and I hope to find a spare knob somewhere in my parts bins.

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Jennifer Petkus divides her time between writing Jane Austen-themed mysteries, creating websites for the dead, woodworking, aikido and building model starships. She has few credentials, having failed to graduate from the University of Texas with a journalism degree, but did manage to find employment at the Colorado Springs Sun newspaper as a cop reporter, copy editor and night city editor before the paper died in 1986. She has done little since. Her husband is the night editor at The Denver Post. Her best friend is a cop. She watched Neil Armstrong walk on the Moon live. She is the author of, Good Cop, Dead Cop: A Novel about the AfterNet. She’s writing the sequel, The Background Noise of Souls, and another AfterNet related story, Jane Austen’s Book Tour.

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