# Gieger Counter lamp - How would I make the needle move/fluctuate when the lamp is on?

Gieger Counter lamp - How would I make the needle move/fluctuate when the lamp is on? I like the instructable Radbear made, but I want to go further and make the needle move when the lamp is on; it would be great if it fluctuates and moves. OR Or how could I make the needle move when someone touches the lamp? I have an old touch lamp that I could use parts for this. The casing for the lamp is metal so I assume their should be a way... Thanks to whom ever can help.

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8 years ago
The meter uses very low voltage and current, and it's DC (v.s the AC that comes out of the main sockets. The first thing to do is get a rough idea of the maximum current needed to "pin" the needle (move it all the way to the top of the scale). You can do this with a single 1.5v dry cell, a potentiometer, and either a milliammeter or an ohmmeter, the milliammeter will give you a direct reading if you wire it in series with the battery, potentiometer, and Geiger counter meter; or you can just wire up the pot, battery, and GC meter and measure the pot's resistance after making the adjustment. The diagram shows connections. The red line indicates the positive end of the battery, black is negative, and the blue line is where you would insert the milliammeter into the circuit. Start with the pot adjusted for maximum resistance and turn it until the needle reaches the top of the GC range (if it doesn't move, you probably have the connections reversed on the GC meter). Once the needle is "pinned," either read the ma meter directly, or disconnect battery and measure the resistance of the pot; use Ohm's law to calculate current. That's step 1. I'll be back to add to the answer shortly.
8 years ago
Now the tricky part. For a simple steady-position reading, you will need a half-wave rectifier (any ordinary silicon diode rated for at least 240V), a resistor which will allow current flow of roughly half the maximum-range current on the GC's meter at your local power line voltage, and some wire. Wire the resistor, the meter, and the diode in series and briefly (like 1 second) connect power. If the needle didn't jump to about half-range, your diode is backwards. Turn it around.

To get a fluctuating reading, you'll want a small capacitor wired across the meter's connections, and - here's the rough part - a frequency-divider circuit to reduce the 60Hz (or 50Hz) AC line frequency down to something you can actually see moving the needle, probably in the 1 to 7 Hz range. That means you need a 4- or 5-stage type D flipflop divider circuit; this can be made very cheaply, but I am not in a place where I can work up the diagrams. Perhaps anotehr reader can help there.

Keep in mind that you are still working with mains input voltages; a cheap-and-cheerful transformer (taking the place of the battery in my original diagram, with the addition of the diode mention above) will make all this much safer. You should be able to find one that puts out 9VAC without any trouble, probably disguised as a "wall wart" power supply for an old modem or something.

DO NOT TOUCH MAINS VOLTAGE WIRES unless you are made of glass or rubber. Trust me, you won't enjoy it.
Bonnonon (author)  MairseyDotes8 years ago
Thanks! :) I will get my buddy to translate me... HEHE If you do get a chance to draw up the second diagram I would appreciate it. I was not expecting an answer so quick and my counter is still in the mail. Thanks again.
Bonnonon (author) 8 years ago
I have posted on his instructable and he doesn't know, thus I am asking the question here. Any other suggestions.
Bonnonon (author)  Bonnonon8 years ago
Where would I find how to make a microphone circuit?
Zengineer16188 years ago
Maybe some sort of microphone circuit hooked up to the meter will do the trick.
lemonie8 years ago
Post a comment on the Instructable - the author will be notified that you've done so. L