Saturday, February 12, 2005

Geiger counter photos



The clicker unit attached to the geiger counter


I made the clicker unit with robust design in mind. Therefore, I epoxied everything to the case and it looks really crappy, but it's not going to fall apart in someone's pocket. You can see the basic circuit--9 volt battery switched, which powers the counter through the phone jack. The detection indicator is a negative voltage swing on another line from the phone jack, which switches a PNP transistor. The transistor opens to allow current to flow through the potentiometer, the headphones, and the speaker. The LED is controlled directly by the indicator pulse, without transistor switching.

What's wrong with the design? The headphones should be bypassed when they aren't plugged in, but they aren't, so the speaker does not click without headphones. And, when the headphones are in, there isn't enough oomph to drive the 8 ohm speaker. I tried bypassing the headphones, but I didn't try until after I had assembled the unit, and everything was too cramped to solder.



P.S. What software tools do you use to generate nice schematics? Preferably free or open-source.

7 comments:

Steven Lucy said...

You could make a "head phone stub" -- 1/8" audio jack with the two wires soldered together -- to use the internal speaker. With luck it wouldn't protrude more than the switch or pot.

colin said...

P.S. What software tools do you use to generate nice schematics? Preferably free or open-source.I've got a copy of LabView from the Computational Physics class. The source code of user-written is similar to a schematic drawing. I think it's possible to print the source code of one's programs. That might work okay if we can't find anything else. I'm not sure how to get LV to run on Linux; my copy might not.

colin said...

Scratch all that about Labview; We want xcircuit. The guy also cites xfig and until. From what he says, xcircuit is designed for elecrical circuits, though you can use it for more general drawing. xfig is supposed to be better for more general drawing.

Dean W. Armstrong said...

Actually, I should mention I want it to run under Windows. Electric and gEDA are also packages that look nice, and they don't have the attitude that xcircuit seems to have with regard to output graphics.

Dean W. Armstrong said...

I found a shorted stub in the RAS office that had a terminating resistor in it, but it still works pretty well. Thanks for the suggestion!

Anonymous said...

Looking for a circuit diagram ... a napkin-drawing scan anyone? (aschiffler at ferzkopp dot net)

Also the URL of xcircuit has changed: http://opencircuitdesign.com/xcircuit/

Dean W. Armstrong said...

I finished up a rough draft at http://dwarmstr.blogspot.com/2007/07/geiger-counter-clicker-schematic.html