Continuing Construction

Finish the construction of the circuit by adding the ICS8 for the555 timer, resistors and transistor. Mount and solder resistors R5 (10 mega-ohm bands brown black blue), R4 (470K bands yellow,purple, yellow,gold) R6 (100K bands brown, black, yellow) and R10 (1 meg ohm bands brown, black, green, gold) by the 555 timer. Mount and solder resistor R7 (47K bands yellow violet orange), R8 (470 ohm bands yellow, violet, brown). Mount and solder R13 (1uf ohm bands brown, black, blue, gold).

Mount and solder capacitors C6 (.001uf), C7 (.047 uF) and C8 (.01 uF) . Mount and solder 120 pF capacitor (C12) by the GM tube. Mount and solder R9 (330 ohm) .Mount and solder C13(.1uf). Mount and solder the Audio switch, power jack, headphone jack and digital output jack. Mount and solder the speaker, Q2, (2N3904) and LED, the longer of the LED terminals is positive (+). to the PCB. The LED should rise 3/8” from the PCB to the bottom of the LED. This distance will insure proper placement of the LED when the PCB is mounted inside the case. Mount and solder the bridge rectifier making sure to align the + terminal of the rectifier to the + terminal on the pcb

Attaching GM Tube

The Geiger Muller tube has two leads. It is mounted on the bottom side of the PCB. The wire connected to the metal sides of the tube is the negative terminal. This is soldered to the (-) GM terminal on the PC board, see figure 7. The center terminal of the GM tube has a removable solder lead. Remove the lead, solder 1.5” of wire to and. Reattach the lead to the center terminal of the GM tube. Take the opposite end of the wire and solder to the (+) GM terminal on the PC board.

The Geiger Mueller tube is delicate and needs to be protected in an enclosure. However the enclosure has a 1/2” hole that allows the front surface (mica window) of the GM tube to remain exposed. This way alpha particles can pass through the thin mica window and be detected.

After securing with a wire a small amount of glue or epoxy can be dabbed on the wire tube assembly for added support. At this point the finished internal Geiger counter PC board should appear as shown in figure 9

Figure 8. Detail showing GM tube secured on PCB

Figure 9

Construction Notes: "Am I Missing Components?

You may have noticed during construction that there are more components that may be fitted to the PC board, such as: C11, Meter, (2) 10K resistors and another PC mounted switch. These components are utilized in other Geiger counters and are not missing from your kit.

Figure 10

Figure 11

Installing Circuit inside Case

Mount the PC board to the front of the case. The shafts of the two PC mounted switch and LED should fit into the pre-drilled holes. The PCB is held to the case front using the two nuts to the PC mounted switches, see figures 10 and 11. Finish by placing the 9-volt battery cap into the battery compartment of the back case. Close the case and secure with case screws.

Features:

HeadPhone and Analog Meter

The headphone jack may be used for a headphones or an analog meter. The analog meter is an accessory that plugs into the headphone jack and provides a visual indication of the approximate radiation level. When using the headphone jack for headphones or the analog radiation meter the speaker is automatically cut-off.

Digital Output

The digital output provides a TTL logic (+5V) pulse every time the Geiger counter detects radiation. This signal can easily be connected to a microcontroller or PC. The PC or microcontroller can then be used to create a digital Geiger counter, chart recorder or other recording instrument for nuclear experiments. Headphone and accessory analog meters may be found on Images website http://www.imagesco.com

Installing /Changing Battery

To install or change battery open battery compartment on the back of the Geiger counter and install or replace battery, see figure 11.

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