Geiger Counter Kit

By Jeff Keyzer
Category: Computers & Mobile, Electronics
Time Required: 2 to 4 hours
Difficulty: Moderate

Commercial Geiger counters can cost hundreds of dollars. Build your own at a fraction of the price! This easy-to-solder kit can be built in an evening and it works just like you think it would; clicking and blinking in the presence of radiation. Just follow the instructions here to build it and use it.

Your MAKE Geiger Counter Kit features:

Detects beta and gamma rays
Serial logging output
Mute button
LED indicator
"Clicker" speaker
Pulse output
ATtiny2313 microcontroller
SBM-20 Geiger-Müller tube
Runs on two AAA alkaline batteries (not included)

Is grandma’s dish collection radioactive? Do bananas give off radiation? Are your granite countertops giving off gamma rays? Build your own Geiger counter and find out! The serial logging function lets you easily track exposure over time, and the mute button lets you silently detect radiation. A must for every mad scientist.

WARNING: This Geiger Counter kit is for EDUCATIONAL PURPOSES ONLY. Don’t even think about using it to monitor radiation in life-threatening situations, or in any environment where you may expose yourself to dangerous levels of radiation. Don’t rely on the collected data to be an accurate measure of radiation exposure. Be safe!

Parts
/
Tools

MAKE Geiger Counter Kit (1) contains all of the following parts:
Geiger Counter Kit printed circuit board (PCB) (1)
ATtiny2313 microcontroller IC (U1) (1) 20-pin package
555 timer IC (U2) (1) 8-pin package
Resonator, ceramic (X1) (1) orange or blue with 3 leads, marked 8.00M or 8.0MC
Piezo Speaker (LS1) (1) round, black, with a hole in the middle
Transistor, FJN3303F (Q1) (1) marked J3303
Transistors, 2N3904 (Q2, Q3) (2) marked 3904
Diode, 1N4937 (D1) (1) the larger, black diode with a white stripe
Diode, 1N914 (D2) (1) the smaller, reddish orange diode with a black stripe
LED, red (LED1) (1)
Resistor, 15Ω (R8) (1) brown-green-black-gold
Resistor, 330Ω (R6) (1) orange-orange-brown-gold
Resistor, 100Ω (R11) (1) brown-black-brown-gold
Resistor, 1K (R5) (1) brown-black-red-gold
Resistors, 10K (R3, R10) (2) brown-black-orange-gold
Resistor, 22K (R4) (1) red-red-orange-gold
Resistors, 100K (R1, R7) (2) brown-black-yellow-gold
Resistor, 220K (R9) (1) red-red-yellow-gold
Resistor, 4.7M (R2) (1) yellow-violet-green-gold
Resistor, variable, 10Ω (VR1) (1) blue with a white screw in the middle
Inductor, 10mH (L1) (1) the small black cylinder marked 103 on top
Capacitor, 220pF (C2) (1) marked 221K
Capacitor, 1nF (C3) (1) tiny, 5mm lead spacing, marked 102
Capacitor, 0.01µF (C1) (1) the biggest disc, marked 103M
Capacitor, 0.1µF (C4) (1) tiny, 2.5mm lead spacing, marked 104
Capacitor, electrolytic, 100µF (C5) (1) black cylinder marked 100uF
Slide switch, (S1) (1)
Push button, (S2) (1) microswitch
Geiger tube holders, (J1, J2) (2) the clips
Battery holder, for 2×AAA batteries (B1) (1)
Header pins, 2×3 row (J5) (1) for the ICSP connector
Header pins, 1 row (J6, J7) (1) to break into 1×3 and 1×6, you may have some left over
IC socket, 20 pins (1)
IC socket, 8 pins (1)
Screw, small (1) for the battery holder
Nut, small (1)
Geiger-Müller tube (1) cylindrical tube wrapped in foam or bubble wrap

Steps

Step #1: Solder the resistors.

To build this kit, you should know how to solder. And it'll be much easier if you've made other kits before. But even if this is your first kit, don't despair! Just take your time and you'll be fine.
If you've never soldered before, Andie Nordgren, Mitch Altman, and Jeff Keyzer of MightyOhm made a fun comic book that will teach you how. You can find it online, translated into many languages, at mightyohm.com/soldercomic.
We recommend soldering one resistor at a time unless you know what you're doing!
The resistors can go in either way — they're not polarized. Bend the leads of each resistor straight down and push them through the holes in the board, then bend them out at a 45° angle to keep the resistor from falling out.
Turn the board over, and solder each lead. Then, cut off the excess leads with your wire cutters.

Conclusion

How to Use It

Easy — turn on the switch and listen for clicks! And watch the LED: it will flash every time a beta particle or gamma ray hits the tube!

NOTE: The tube that comes with this kit is not sensitive to alpha particles. However, the kit is compatible with other tubes that do detect alpha.

Mute: If you get tired of hearing the clicks, you can push the button S2 to mute the sound.

Pulse connector: The pulse connector (J6) has the following pinout:

1. VCC (nominally 3V)

2. Pulse output — a short (100µs) active high pulse every time the Geiger tube fires

3. GND

For more information, design files, source code: mightyohm.com/geiger

Logging

To connect your computer to the serial port (J7), you'll need a USB-serial converter that operates at 3.3V TTL levels. The serial header is set up to work with the common FTDI-232R-3V3 serial cable.

Data is sent over the serial port at 9600 baud, 8N1. The data is reported in comma separated value (CSV) format:

CPS, #####, CPM, #####, uSv/hr, ###.##, SLOW|FAST|INST

There are three modes. Normally, the sample period is LONG_PERIOD (default 60 seconds). This is SLOW averaging mode. If the last 5 measured counts exceed a preset threshold, the sample period switches to SHORT_PERIOD seconds (default 5 seconds). This is FAST mode, and is more responsive but less accurate. Finally, if CPS > 255, we report CPS*60 and switch to INST mode, since we can't store data in the (8-bit) sample buffer.