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 ICS16 for the 4049, marked U1 on PCB Insert the ICS16, making sure to orient the notch on the socket to the drawing on the PCB and solder to the PC board. Place and solder components R1, R2, R3, C1, C2, and D1. R1 is a 4.3K resistor having the bands yellow orange red. (For help with the resistor color code see appendix at the end of this article.) 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, diodes D2, D3, and capacitors C3, C4 and C5.
Mount IRF830 transistor Q1 to the PCB, bend the transistor outward so it lays flat on the PCB, see figure 6, and solder. To this add the 5 volt 7805 regulator (Q3), bending it outward so it lays flat, as with transistor and solder into position. Next mount and solder capacitor C10 and diode D9 1N4007. Place and solder the 9-volt battery cap on the PC board. The red lead connects to the positive terminal by D9. The black lead connects to GND. Solder the power switch to the 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 7 . 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.
Build Your Own Geiger Counter pg 6 "Geiger Mueller Tube"
Digial & PC Geiger Counter Analog Meter Geiger Counter Analog Geiger Counter Geiger Counter Kits
