Students often asked us plans of Geiger counter to build oneself. To answer this request a simple assembly schema is proposed.

click on picture to enlarge

Components list :

- GM : Tube Geiger LND712
- T1 : Transfo 220V 2x6V MYRRA 44199
- J1 : Prise femelle DB9
- U1 : IC MC14538
- BUZ1 : Buzzer Euroind 242B
- D7 : Led low power
- D1, D12 : 1N4148
- D2, D3 : 1N4007 or fast recovery diode 1000V
- D10, D16 : BZX55C-200V
- D17 : BZX55C-100V
- C1, C9 :100nF 50V
- C2 : 4,7 µF  25V
- C3 : 470pF 1KV
- C4 : 22nF MKT 630V
- C5 : 100pF 1KV
- C6, C7 : 22nF 50V
- C8 : 47pF 50V
- C10 : 470 µF 25V
- R1 : 1R
- R2 : 47K
- R3 : 470R
- R4, R8, R9, R10, R12, R13 : 1M
- R5, R6 : 10M
- R7 : 10M 1KV
- R15, R30 : 5K6

Cable RS232  DB9F/DB9M

Attention : high tension is measured on some components.
For measuring the tensions, use an oscilloscope probe 100Mohm 1500V

F.A.Q.

The Geiger counter does not send any signal.

Check-up the plugs on the serial port. The software must be programmed for the serial port which you use. Make sure that the cable is in a good condition and there is not internal cut after installation it through a door or a window. Change the cable if it was damaged. The 9/25 pins adapters for mouse cannot transmit the signal to the computer, use only an adapter for modem.

Could I put the Geiger counter out of the window.

The Geiger probe could be installed out if it is not exposed either to humidity or to rain. The best place to fix the Geiger probe is on the top of the window, in shelter, behind a shutter. You must make sure it is waterprofed by putting it in a plastic bag.

The Geiger counter is wet and does not function correctly.

Let it dry completely. If it is doesn't work, you should repair it.

The Geiger counter detects radioactivity when it is not near a source of radioactivity.

If the Geiger counter is humid let it dry. Verify that it is not contaminated with radioactive dust stuck on the equipment. Verify that the background radioactivity level is normal.

I have stuck the cable under a window and the Geiger counter does not function.

If the cable is damaged, it must be cut off the equipment. In this case, you must replace it. You can buy it from any electronic or computer shop.

I need a longer cable.

You can use a long distance RS232 transmiter.

The software does not seem to be functionning correctly.

Install again the software.

How to check-up the correct Geiger counter function.

The natural radioactivity level is between 0,010 mR/h et 0,040 mR/h, depending of the area where you live. You can use a gas-mantle of camping gas light. These gas-mantle have the particularity to be little radioactive. The new gas-mantle with "no radioactive" mention cannot be used for this test.