PROJECTS: GEIGER COUNTER
makeprojects.com/v/29
MAKE IT.
BUILD YOUR
GEIGER COUNTER
Time: A Weekend
Complexity: Moderate
1. ASSEMBLE THE PCB
1a. From your GM tube’s
specifications, note the voltage required to drive it. This
should be an even hundred
number between 300 and
600 volts. Match this number
by totaling the values of up
to three 100V or 200V Zener
diodes; for example, use two
200V Zeners and one 100V
for a 500V tube.
1a
1b. Solder the Zeners into
positions D8–10 on the
circuit board, following
correct polarity. Fill D8 with
a 100V Zener, if used. Nearby
jumper J1 bypasses D8, which
lets you quickly adjust the
tube voltage down 100V.
1b
1c. Find the values for anode
and cathode resistors R5 and
R4 by referring to the specifications for your GM tube.
For the tubes I stock, the
recommended anode resistor
value ranges between 2.2MΩ
and 10MΩ. The LND 712 tube
shown in Step 2a needs a
10MΩ anode resistor and
a 470KΩ cathode resistor.
Solder resistors R5 and R4
where indicated on the PCB.
1c
John Iovine
104 Make: makezine.com/29
