Topband: Re: Vactrols and Flag

[Ford Peterson]

I've been looking at building a set of 3 pennants this summer.  Doing some
experimenting will some Radio Shack Cadmium Sulfide photo-resistors and
green LEDs I find that the response appears to be similar to what is
expected from the "Vactrols" at a minute fraction of the cost.

Radio Shack sells an experimenter's kit of Cad/Sulfide parts for a couple of
bucks.  Playing with some various LEDs of different color and intensity, the
response appears on an Autek VA1 to be about 300 ohms to 3K ohms and only a
few ohms of capacitive reactance (maximum).  The reactance may be more
attributable to the test fixture/instrument than the part.

I just place the leads of the Cad/Sulfide cell into a 1/4" - 3/8"  diameter
foam plug and place the unit inside some shrink wrap with an LED on the
other end.  The response is quite linear if you use a resistor on the LED to
bring the voltage range up to a few volts instead of the LED's linear range
of about .2 volts.

Any body else played with these?

Ford-N0FP
ford@cmgate.com