Lately I have been messing around a bit with microprocessor powered geiger counters. One smart guy came up with the idea of generating high voltage using PWM signals from the microprocessor itself. With some additional external parts a HV supply and negative going pulse suitable for microprocessors is easy to make. H
…The circuit works as follows: A ~1 Khz squarewave turns the MPSA44 high voltage transistor on and off, generating high voltage when the inductors current is shut off. The voltage depends on the pulse width of the square wave which can be tweaked in software. The 1N4007 diode rectifies this voltage, and the HV cap removes most of the ripple on this voltage. The resistor limits current to the GM tube. The current pulses from the tube generate a voltage drop over the 100K resistor which turns on the BC546. When this happens the voltage through the 10K resistor is pulled to ground, generating a negative going pulse each time the GM tube detects an ionizing ray or particle.
To drive this circuit I used my new Adafruit Trinket, a small board with a Attiny85 microprocessor. Using the tutorials on the Adafruit website it is easy to work with from the Arduino environment….
Adafruit Trinket – Mini Microcontroller – 3.3V Logic: Trinket may be small, but do not be fooled by its size! It’s a tiny microcontroller board, built around the Atmel ATtiny85, a little chip with a lot of power. We wanted to design a microcontroller board that was small enough to fit into any project, and low cost enough to use without hesitation. Perfect for when you don’t want to give up your expensive dev-board and you aren’t willing to take apart the project you worked so hard to design. It’s our lowest-cost arduino-IDE programmable board! The Attiny85 is a fun processor because despite being so small, it has 8K of flash, and 5 I/O pins, including analog inputs and PWM ‘analog’ outputs. We designed a USB bootloader so you can plug it into any computer and reprogram it over a USB port just like an Arduino. In fact we even made some simple modifications to the Arduino IDE so that it works like a mini-Arduino board. You can’t stack a big shield on it but for many small & simple projects the Trinket will be your go-to platform. (read more)
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