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Home > Articles >Build Your Own Geiger Counter, Page 5
Construction
You
may hardwire this circuit to a breadboard or use the available PCB
board. Although you do not need the PCB, the PCB will may construction
easier. The top silkscreen of the PCB is shown in Figure 5.
Begin construction by wiring the square wave generator and pulse
shaping circuit using the 4049. Solder the 16 pin IC socket for the
4049. Place and solder components R1, R2, R3, C1, C2, and D1. R1 is a
4.3K resistor having the bands yellow orange red. R2 is a 15K resistor
having the bands brown green and orange. R3 is a 5.6 K resistor having
the bands green blue red. Now construct the high voltage section
consisting of the step up transformer T1, IRF830 transistor Q1, diodes
D2, D3, and capacitors C3, C4 and C5. To this add the 5 volt 7805
regulator (Q3) and capacitor C10. Place and solder the 9-volt battery
terminals on the PC board and diode D9 (1N4007). Connect the SW1 power
switch, using 6” leads of wire. Insert the 4049 IC into the 16 pin IC
socket soldered to the PC board.
Figure 5. Detail of top screen on PCB
Testing High Voltage (HV)
CAUTION:
Circuit generates high voltage power that can provide an electrical
shock. Exercise caution when working around the high voltage section of
the circuit. The capacitors C4 and C5 can hold a HV charge long after
the circuit has been shut off and can therefore still provide an
electrical shock. If you are uncomfortable working with high voltage
you can skip the HV testing section.
At this
point in the construction you can check the HV power supply. Turn the
SW1 power switch off. Insert the 9-volt battery onto the PC board. Set
up a Volt Ohm Meter (VOM) to read 500 to 1000 volts. Place the positive
lead of the VOM at the junction of C4 and D2. The negative lead of the
VOM is connected to the—(negative) terminal of the 9-Volt battery.
Apply power to the circuit using SW1, see Figure 6.
The circuit should generate anywhere between 550 and 800 volts
(depending upon component tolerances) If you are reading between 550
and 800 volts, fine, turn off the power. Add the three zener diodes
(D4, D5 and D6) used for voltage regulation. Apply power again, with
the positive lead of the VOM still attached to the junction of C4 and
D2 you should read a voltage of 500 volts. If you're not getting a
proper voltage reading, check the zener diodes to make sure you have
them orientated in the right direction.
Figure 6. Circuit board ready for HV test
Build Your Own Geiger Counter pg 6 "Continuing Construction"
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