Instructables

How To Make A Fake Geiger Counter

Picture of How To Make A Fake Geiger Counter
What sound effect can enhance a mad scientist's lab at Halloween?  The ticking of a geiger counter!  And imagine...What if you had a fake geiger counter you could wave over anything, and whenever you wanted, set off furious clicking? 

That's what I built for our Halloween party last year.  We had a guided tour, where the resident mad scientist took people around in a small group.  When they got to the toxic waste dump, they were "checked out" with the fake geiger counter...and wouldn't you know it?  Some of them were already exposed before they came.  Tsk, tsk.

It turns out that a low-key, realistic effect like this will creep people out much more than a lot of traditional stuff (I speak from experience.)  A skeleton popping out of the ground?  Eh.  A zombie munching on an arm?  Cute.  I've been exposed to radiation?!  AAAHHHHHH!

After searching the web, it seems that no one has created a live geiger counter sound effect generator.  You can find short sound clips of geiger counters, but they're only a few seconds long and they sound like a recording, plus if you used one it would repeat the same pattern over and over.  I wanted a hand-held device that would generate the sound effects live.

This is an extremely accurate simulation of the real thing.  I've shown it to people who work with radiation in their jobs, and they've all said, "Yup, that's what it sounds like."

Check out this video:


There are two parts to making this - the electronics and the geiger counter prop itself.

Electronics Sound Effects Overview

This is powered by an Arduino.  When you turn it on, it makes a slow, "background radiation" clicking sound effect.  Press the button and the sound effect rapidly ramps up to an alarming rate.  Release the button and the clicking goes back to normal.  There's also an optional LED that acts as a power light and flickers with the clicking, but the unnerved Trick-Or-Treaters didn't seem to notice it.

The Arduino generates a randomized clicking on one of its pins.  This is sent to a small LM386 amplifier which boosts the volume, and powers a mini 8 ohm speaker.  I tried connecting the Arduino directly to the speaker, but even with a capacitor, you can barely hear the clicks, so I added the LM386 circuit.

UPDATE, 5/22/2013:
I've found a pre-made mini audio amp that is better than the LM386, and is really cheap.  See the last step.
 
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danisparx1 year ago
i have just finished building this but it's r quiet any ideas as to why?? or a solution to make it louder, need it for mid next month and my knowledge is lacking Thanks
Jeff Haas (author)  danisparx1 year ago
Make sure you use the amp, if you don't use that, you get a very quiet clicking sound. I also had to try a few different little speakers to get one that performed well.
i made the amp as per your design then i also checked a couple of other sites about the LM386 chip and found the gin could be adjusted witn a cappy between 1 and 8 and then a pot in series but even trying that i cant get any real sound from it??
ok maby when i follow all the design and check my work properly ill realise to ground pins 2 and 4 lol that helped but im still not loud enough?? im going to be using it at a party so need a lil more volume if u know a way to max this or should i build another one and drive one into the other amp??
Jeff Haas (author)  danisparx1 year ago
Glad to hear you fixed the amp. I made a lot of the same kinds of errors when I was first building circuits.

I'm on the road right now, so I can't test this, but I think you could take the output from the LM386 amp and put it through a set of computer desktop speakers, instead of into the small 8 ohm speaker. It depends on if you want to make a hand-held device or just need the sound effect for the background.

You can also try the more advanced versions of the LM386 circuit on the datasheet and see if they give you enough volume, but I think that might not be as easy as using the computer speakers.
well its all up and running now i used a 8 ohm speaker and a 10 uF cappy across 1 and 8 also i took the output off the diavalino and the ground to pins 2 and 3 and powered the amp with a seperate 9V pp3 Battery and it got loads louder but i did suffer with more background noise, also i used a simple sound to light (LED) circuit and made a dial to show the levels of radiation, it looks pretty cool to be honest, thanks
Jeff Haas (author)  danisparx1 year ago
That's awesome, good to hear you solved it. And I like the idea of using the sound-to-light circuit to make the dial light up. If I'd had more time when I was making this (and I'd thought of it) I probably would have done it too.

Put some pictures and a video of your final build up, it sounds cool.
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