Geiger Counter Enhancements & Options
In the following sections you will find enhancements and options for the basic Geiger counter.
We have a revised schematic shown in Figure 1. The basic Geiger counter circuit is identical to the previous circuit. The revision is the adding of the components for our three optional enhancements; external power input, headphone jack and digital output, boxed in red.
External Power – The external power is designed to allow a wide range of wall transformer to power the Geiger counter. Wall transformers that can supply a minimum of 75 mA with voltages that range from 7-12VAC or 7-12VDC will work. The bridge rectifier is rated at 25V 1 amp. Pretty much any bridge rectifier with specifications around these specifications (or better) will work when placed inside the circuit. The positive output lead of the bridge rectifier is placed after the D9 diode. The D9 diode protects the battery when using external power.
Headphone Jack – Aside of its obvious use for a headphone, this jack may also be used as a temporary output for an Analog Meter. The headphone jack is a 3.5mm 2-conductor jack with a SPST switch. The switch automatically disconnects the speaker when the headphone or analog meter is plugged in.
Digital Output – The digital output jack provides a +5V TTL logic pulse every time a radioactive particle is detected. The digital output uses an unused gate off the 4049 as shown in the schematic. We will build a small interface between this output and a Windows PC. This will allow you to use one of the free Geiger counter graphing programs.
For those who have purchased the PC board for this project, the enhancements may be added by wiring in the three jacks as shown in Figure 2.