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.

Step 1: Electronics schematics

This is quick to assemble on a breadboard.  Note that you should click on the schematic and view the original size, so you can read all the notes clearly.

Electronics parts:

- Arduino.  I used the "Diavolino" from Evil Mad Science:
If you use this you'll also need an FTDI cable to program it, see their site for details.  Not only is it inexpensive but the Evil Mad Science people have lots of other cool kits.  Check out their Larson Scanner!
- Battery box.  The Diavolino can use one that holds 3 AA batteries and this lasts much longer than a 9V.

- LM386 Low Voltage Audio Power Amplifier.  This is a classic chip, available at Radio Shack, Jameco, etc.
- 220nf capacitor
- 220uf electrolytic capacitor
- 8 ohm speaker.  I had a few surplus speakers, but none of them were good enough.  I finally used a quality one that's loud, Jameco Part no. 135589.

- Pushbutton, momentary on.  One of these: http://www.radioshack.com/product/index.jsp?productId=2062539
- 2.2k resistor

- LED.  I used red.  This is optional but adds a nice touch.
- 330 ohm resistor

- On/off switch.  This is spliced into one line from the battery box to the Arduino.

After testing the circuit, I built the LM386 amp on a small Radio Shack project board, and included the connections for the button as well.  This was to save space in the project box.
<p>I ended up building mine in an old 720 civil defence meter, based on the instructions from &quot;The Tinkerers Apprecentice&quot; below. Used an Adafruit Mono 2.5W Class D Audio Amplifier - PAM8302 (https://www.adafruit.com/product/2130), and works perfectly ($3.95), and a barebones arduino.</p><p>Has anyone ever mad any luck in getting the old Civil defence round meter to work via PWM or something else - this would be perfect. The meter is marked as 50 micro amps, but I don't know it's internal resistance</p>
<p>Hi all</p><p>I've just made one of these with an Arduino UNO, and it works fine, except sometimes seems to spontaneously go into &quot;detection&quot; mode i.e. as if the button has been pressed, but it hasn't. I can't read this style of Arduino code - anyone have any suggestions?</p>
<p>Double-check the way you've got the button set up - it needs the pull-up resistor connected as in the diagram. Otherwise you might be false triggers.</p>
<p>it's interesting that you have to resort to an Arduino. there really seems to be no analog schematic for a geiger counter sound effect. i guess one would need a source for shot noise with adjustable frequency, but it really does not appear to exist.</p>
<p>There were no analog circuits I could find when I first started this project. Your comment got me to search again...I turned up two newer projects that create similar sound effects, but with much less control and fidelity to the sound of a real geiger counter.</p><p><a href="http://www.instructables.com/id/Using-a-candle-flicker-LED-as-a-quasi-random-squar/" rel="nofollow">http://www.instructables.com/id/Using-a-candle-fli...</a></p><p><a href="http://www.interestingelectronics.com/old/henrys_interesting_electronics/xmas_lfsr/xmas_lfsr.html" rel="nofollow">http://www.interestingelectronics.com/old/henrys_i...</a></p><p>The advantage of an Arduino is that there is software control over the effect, including the ramping up and down of the clicking when the button is pressed. Also, some physics formulas were used to get the right type and rate of clicking.</p><p>And since I posted this in 2012, Arduino clones have become very inexpensive, which makes this way of doing it less trouble than wiring up a circuit yourself.</p>
<p>Thanks to Jeff i made my counter version for STALKER LARP.</p><p><iframe allowfullscreen="" frameborder="0" height="281" src="//www.youtube.com/embed/W_DCTUURDM4" width="500"></iframe></p>
I'm going to check eBay for one of those GCs. For an aiduo amp, all you need is a transistor and a resistor or two. Pulses are easy to amplify.
Very nice!<br><br>Do you mind showing what you did to make it look that way, and the other internal details (like the gauge on the top)?
<p>(sorry for my english)</p><p>Most interesting <br>part is &quot;magic eye&quot; tube. It was used in old sound amplification <br>circuits, but this one i bought in ebay. It works on +12vdc so i have to use big <br>12vdc accumulator. There are two audio amplifiers: one PAM8403 board and one <br>from old PC speakers which have sound <br>level knob. Through bigger amplifier i ran bigger speaker and tube driver, <br>through smaller amplifier i ran second speaker and sound value meter(which i <br>found in broken big amplifier)</p><p>And i have done <br>little changes in C code to make LED blink depended on sound.</p><p>Box is just <br>ordinary electric distribution box which i painted in green.</p>
<p>Thanks for the info and the pictures! I didn't know what a Magic Eye tube was before this. I found this article on Wikipedia which explains it:<br><a href="http://en.wikipedia.org/wiki/Magic_eye_tube" rel="nofollow">http://en.wikipedia.org/wiki/Magic_eye_tube</a></p><p>I'm sure people reading this will want to know what updates you made to the C code. If you have time, please upload it here.</p><p>Also, your use of the Magic Eye gives me an idea, for people reading this in the future - I think you could use an LM3914 to drive an LED bargraph to get a modern version of this display. See info at Sparkfun:<br><a href="https://www.sparkfun.com/products/12694" rel="nofollow">https://www.sparkfun.com/products/12694</a></p>
<p>Sorry for late response, but i have lot of work nowadays. So difference in code its just one word in 143 line. Need to change from &quot;shift&quot; to &quot;sit&quot; in 143 line: &quot;led_out(sit);&quot; For next year i thinking to add battery voltage meter like http://www.ebay.com/itm/181411771928?_trksid=p2059210.m2749.l2649&amp;ssPageName=STRK%3AMEBIDX%3AIT or http://www.ebay.com/itm/181012882590?_trksid=p2059210.m2749.l2649&amp;ssPageName=STRK%3AMEBIDX%3AIT . It makes me lot of fun:)</p>
<p>Also this tutorial on the chip is good:<br><a href="http://tronixstuff.com/2013/09/14/tutorial-lm3914-dotbar-display-driver-ic/" rel="nofollow">http://tronixstuff.com/2013/09/14/tutorial-lm3914-...</a></p>
<p>Were is the sparkling LED with the &quot;e&quot; and the atom-symbol in the left-down-corner coming from?</p>
<p>Hi Jeff,</p><p>Sorry this took so long to get posted, I've been in a rush to get the rest of my mad scientist's lab ready! Here's the pics of my modified Geiger Counter, using your fabulous instructable! I just followed it exactly and everything worked first time =) First off, I just clipped a couple of wires and unscrewed the original guts to make room for my new ones. Then I unscrewed the original &quot;zero&quot; knob and mounted my switch there. I had to drill a few holes in the Geiger Counter for the button at the tip of the handle, and then holes for the speaker (I really did have a pattern set out for the speaker holes, not sure what happened to it during the drilling though, lol). I hot glued the speaker directly to the case, making a good bead around the lip of the speaker, and hot glued all open electrical connections for insulation. And finally, I mounted the electronics with sticky velcro to keep it insulated from the case. </p><p>Thanks again for the inspiration and clarification on my questions! </p><p>Holly</p>
<p>Wow, that's pretty impressive. </p><p>FYI to other readers...there are a lot of these old geiger counters on ebay.</p>
Hi Jeff,<br> Thanks for this project! I'm wondering, if I use the mini digital amplifier board, do I still need the capacitors and if so, where do I place them? Thanks for the help, I'm planning on making this using an actual old style Geiger counter for my mad scientist lab this year!
<p>Good question. I just re-tested this - you don't really need the capacitors if you're using the small audio amp.</p><p>I solder short wires to the audio board and power it from the Arduino. The 5V and GND in the center go to those connections on the Arduino, and the RIN (for Right speaker in) takes the connection from pin 10. Then R+ and R- on the audio board go to your speaker. An old computer speaker works fine, but I tried a few, and the best was the heaviest, because it had the biggest magnet on the back. If the speaker is in a closed compartment, it will sound better, since all the sound will be reflected out.</p><p>And please post a video of your completed project! It will be interesting to other people here to see how you modified the old Geiger counter.</p>
Thanks so much for the quick reply! I'll be sure to post pics or video of my completed project, I'm just waiting on the speaker to come in and then I'll get started on it! Thanks again.
<p>I would like to make one, but I am a noob at Arduino. Someone gave me an Adafruit Gemma board. From what I can tell, it's basically a severely stripped-down version of the regular Arduino boards. Can it be used for this project? </p><p>When I try to load you code, it gives me an error message. I assume it's either an error on my part, or the Gemma board can't run the code.. </p><p>'TCCR1B' was not declared in this scope.</p><p>FUMH43DH2MYLUI4.ino: In function 'void stop_timer1()':</p><p>FUMH43DH2MYLUI4:45: error: 'TCCR1B' was not declared in this scope</p><p>FUMH43DH2MYLUI4.ino: In function 'void start_timer1()':</p><p>FUMH43DH2MYLUI4:50: error: 'TCCR1B' was not declared in this scope</p><p>FUMH43DH2MYLUI4:50: error: 'WGM12' was not declared in this scope</p><p>FUMH43DH2MYLUI4.ino: In function 'void set_compare_timer1(uint16_t)':</p><p>FUMH43DH2MYLUI4:62: error: 'OCR1AH' was not declared in this scope</p><p>FUMH43DH2MYLUI4:63: error: 'OCR1AL' was not declared in this scope</p><p>FUMH43DH2MYLUI4.ino: In function 'void ioinit()':</p><p>FUMH43DH2MYLUI4:156: error: 'TCCR1A' was not declared in this scope</p><p>FUMH43DH2MYLUI4:157: error: 'TCCR1B' was not declared in this scope</p><p>FUMH43DH2MYLUI4:163: error: 'WGM12' was not declared in this scope</p><p>FUMH43DH2MYLUI4.ino: In function 'int main()':</p><p>FUMH43DH2MYLUI4:178: error: 'TIMSK1' was not declared in this scope</p>
<p>The Adafruit Gemma has a different processor than a standard Arduino. It's designed to be a very small board that is used in &quot;wearable&quot; projects and sewn to clothing. The processor has much less memory and doesn't support all the same features as the chip on a regular Arduino.</p><p>If you want to do this project, you'll need to get a standard Arduino or Arduino clone.</p>
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
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??
Glad to hear you fixed the amp. I made a lot of the same kinds of errors when I was first building circuits. <br> <br>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. <br> <br>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
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. <br> <br>Put some pictures and a video of your final build up, it sounds cool.

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