[dorkbotsea-blabber] Radio Shack design contest

[Steve Greenfield]

I've entered a design contest sponsored by Radio Shack for a $250
gift certificate. The concept of the contest: simple projects
buildable with parts from Radio Shack. Not easy, since they dropped
so many parts.

This is my entry:
http://rsinventionlab.com/archives/95
Click on the thumbnail to see the full size schematic.

It is a device for measuring capacitance. It connects to a DMM to
use it for the display device, because often the single most
expensive part of a bit of test equipment is the display itself.

I'm over 100 votes this morning, way more to go to beat the one I
saw with close to 200.

Apr 15th was the deadline for submissions, voting will go on for
another week or two.

I wish I had thought to say this part in the article, so I added it
as a comment below it:

This can also be used as a noncontact or contact capacitance switch
by connecting a comparator in place of the meter. Detect someone
touching a doorknob or panel, or detect someone getting close to a
door by taping a sheet of foil to the inside (won't work on a metal
door).

I've used this circuit as a liquid level detector. Drop two
insulated wires into a container, spaced about a 1/4 inch apart.
Zero the meter reading with the tank empty. Fill the tank,
calibrate to 100mV, which will now stand for 100%. Tada! As long as
the wires are straight and parallel, it should be very linear.

You can also build a Theremin using two of these. Build two of
these circuits. Run the output of one to a VCO (Voltage Controlled
Oscillator), the other to a VCA (Voltage Controlled Amplifier).
Tada! Frequency and volume control. Connect each to it's own
antenna/hand sensor.

http://rsinventionlab.com/archives/95

If you like my project, consider voting for it.

Steve Greenfield