Figure 6 PCB in the bottom of CDV-715 case for marking mounting holes.
Do the same for drilling the holes for the 9V battery holder and GM Tube holder. The GM Tube holder I used was a 3/8" plastic cable holder. If I were using the LND712 GM tube I'd use a 1/2" plastic cable holder. Construct the Geiger counter board as per the instructions in the original article. There are a few minor changes are required You do not need the terminal block(s), the S1 switch or the speaker switch. The speaker switch should be jumped in the on position. (Alternatively, you could mount an external audio switch.) The S1 switch is replaced with an external rotary switch that is described in better detail later on in the retro-fitting section. You can solder two 9" wires in the S1 position for connecting the external switch. The terminal blocks are not needed, the pulse in wire from the Analog Digital meter is soldered directly into one of the "D" (digital output) pads used for the terminal blocks.