This project is based on a Maxim Integrated app note. This circuit uses a photodiode to detect gamma photons. When a gamma photon strikes the photodiode the signal is amplified by several low noise op amps and the final signal is fed to a comparator that pulses high at a certain threshold. I won't go into the details about how it works - read the app note and do a google search. There are many projects on the internet that use this identical circuit. Instead, I will focus on how to interface this circuit with the SAM4S Arm Microcontroller. I have prepared two PCBs for this project. The first is just the circuit on its own to make sure it works and the second is the same circuit, but with a different photodiode and the SAM4S on the same board. The PCB's hole placement was designed to put into this hand held enclosure. An LCD screen will be mounted on the enclosure to display a graph of the data as well as a count per second.
I will make the boards and BOM available as well as the fully populated boards available when finished.
Download PDF Note: There is a mistake in this schematic. I need to condition the signals to the MCU from 0-5V to 0-3.3V.
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I will upload when complete