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This project is my response of the need of an universal high voltage power supply to be used with mostly all type of geiger tubes that I have in my collection.
I've needed a selectable output voltage between 300V and 900-1000V, low power output, on board pulse counter and maybe a display. All powered by 5V
It must be flexible allowing usage as stand-alone geiger counter, OpenHAB geiger sensor and also as module for Arduino/Raspberry
Weight: <15 grams with OLED
Input: 5V stabilized @ 10mA with OLED (much lower current without)
Output short circuit current @ 200V: 16uA
Output short circuit current @ 900V: 75uA
Built-in 10Mohm anode loading resistor for geiger/PMT tubes
Built-in but excludible katode pulse sensing/conditioning circuit for geiger/PMT tubes
4 bit parallel interface for voltage selection. Must be drived by open collector/drain interface
4 bit jumpers for voltage selection
UART interface for data logging
0.96" OLED display as optional
I've started the design of this voltage converter scrapping my "Madexp PMT adapter" power supply section. For more info visit www.madexp.com
In that old project I've generated 900-1600V with a single 5V source from USB via a simple TTL variable duty cycle oscillator.
I've replaced that oscillator with an Atmega328P MCU so I'm capable to add programmable voltage output via 4 bit parallel interface, pulse counting and if I need, an 0.96" OLED display.
The board is thinked to be used as a module for a bigger project or as stand alone.
As module of a bigger project, you can simply omit the OLED display and connect the 8 pin connetor to your hardware. The 4 bit parallel interface selects voltage output and the ACK pin goes HIGH when the output voltage selected is reached/stabilized. You need to drive the parallel port with open collector/open drain interface because of pull-up resistors on the interface. Usually it connects with Raspberry/arduino without problems. The logic 1 "HIGH" is 0V, logic "0" LOW is 5V again, because of the pull-up resistors.
If you wish to use the module as stand alone, you can connect the OLED and a geiger on the + and OUT pins, 5V supply from a battery (voltage regulator NOT included) and you can see the voltage, pulses per minute (CPM) and last minute reading on the display. The output voltage is selected by make a soldering bridge on voltage selection jumpers. The bridge shorts the input pull-up to ground asserting a logic HIGH. It permit you to made a pocket size geiger counter with very low effort. Just remember that the circuit needs 5V input no more, maybe something less... at 3.3V it lights up but don't works.
Another example, if you wish to made a geiger clicker without display you cold simply connect a little speaker between pin 1 of the 8 pin connector marked as "^" and GND, omit OLED. Each ray that will hit your geiger tube will made a click on the speaker.
The 3 pin output connector have a geiger katode connection marked as "OUT" and also permit you to exclude the pulse counting and conditioning section connecting the powered item directly between HV and GND.
Possibility are too many to list here... just think that you have also an UART port that each second output a pre-formatted text string. It could be connected on an existing OpenHAB network as a sensor!
There is also a JTAG connector for uploading new firmware via a USBAsp programmer. During operation the jtag pins 3 and 4 becomes RX/TX uart. Pin 1 is GND.
The voltage selection jumpers are made to select output voltage. Jumper 4 is LSB and 1 is MSB of a 4bit value (0-15). To select output voltage you can simply multiply the binary selected number by 50 then add 200V. Look at the table below
The firmware is in currently developement but it's already stable, counts pulses, display voltage and also send info like pulses/voltage via UART.
Risks and challenges
There are no risk at all. I'm just ready to made 50 board after receiving founds within 1/2 mounths.
At the moment I'm waiting the new testing PCB's, black backround, white text and gold plated traces/contacts. They will arrive in 2 weeks.
At 99% they will be the definitive PCB for production and I've ordered 40.
My components supplier is Mouser. All is ready to production just I need money to buy components, make the boards and ship out.
You'll receive a fully assembled and tested board with OLED display soldered in place. Included pin strip but not soldered in place. Shipping fee is for registered air mail with tracking number. Because I need to order new components there is some 2-4 week shipping delay for items of this reward