MadExp PMT adapter

UPDATE 18 Feb. 2018
I've analyzed my home radioactive background simply leaving the MadExp PMT connected and running for 100 minutes on the table top. The result is this:

UPDATE 10 Feb. 2018
I've completed my first example of MadExp PMT adapter and it's NaI(Ti) probe. I'm making some test with it. Three audio samples was recorded with it and are listed below.
This one is my location gamma backround
This is an Am241 alpha emitter capsule from smoke detector
This is the sound of an highly active (15mSievert/h) Pechblende uranium ore

In this video you can see my first PMT test.

How to power and aquire signal of a scintillation probe?

You I need some high voltage and signal conditioning circuit! Inspired by the Theremino PMT project, I’ve decided to build my own customized version of their circuit.

My project goal is to make an all-in-one photomultiplier tube power supply and audio ADC powered by a single USB cable. The high voltage generator is regulable in the range 700-1500V with a simple trimmer.

Corrent status of the project:

  • Schematic at version 2 (erros corrected)
  • PCB routing ready
  • First batch of PCB’s arrived from chinese manufacturer
  • First complete prototype ready and working
Schematic V2.0

To enlarge the schematic right click on the image and select “Show Image” or download it and zoom with your image viewer.

In order to make the CM108AH working you absolutely need to add the 47 ohm series resistors on USB D+ and D- data lines with a pull-up resistor of 1.5K from the ic’s 3,3V out to D+. I’ve lost a lot of time to understand this simple thing… but not so obvious!

This is the PCB board top layer

With my CNC engraver I’ve made some engravings to the PMT adapter enclousure… as a first test I’ve messed with the cutting deep/speed.

The video below is my first test of the circuit

First test connecting the adapter to my pc soundcard. The program is Theremino MCA, is not calibrated… I need to set each control of the MCA at the right position so I need some time for setting up it.

Testing a camera lens containing thorium
Testing a natural Pichblende sample from a mine situated in northen Italy.

Homebrew a Geiger rate meter

Hi! In order to count pulses generated from Geiger tube when striked by a ray, we need a counter. If we combine a pulse counter with an high voltage supply for the Geiger tube, we have made a rate meter.

This is my inplementation:

Homebrew rate meter for geiger tube

On the left there is the power on/off switch and the BNC female connector where you connect the Geiger probe. In the center the 16×2 LCD display shows on the top line the result Counts Per Minute (CPM) of the… last minute. On the lower left there is a 60 second countdown to show how much time remain to update the CPM line. On the lower right there are the total pulses counted from the last 60 second countdown. It reset each 60 seconds. On the front panel, top right, you can see the voltage selector (400/1000V) to power the tube. The 1Kv position is for photomultiplier tube. The “pulse” RCA connector is used to send the tube pulses, amplified, to a PC soundcard or other devices for future use.

HV main board lower side
HV power supply plus linear regulators and pulse amplifier










The HV section is very simple, a single transistor oscillator that drive a CFL lamp transformer from an old LCD display. The rectified output is leveled by a series of zener diodes and filtered by a C-R-C-R-C network of 10nF@2Kv rating blue disk cap. and 1Mohm 1/4W tru-hole resistor.

HV power supply schematic, CRC filter omitted. 5V supply filter omitted too…

The output noise is down below 4mVpp at 1000V!!! with 80-100Megaohm load. The pulse amplifier is used to reverse the pulse polarity from negative to positive, enlarge it and drive the counter circuit. I’ve copyied it from the Theremino website at the section  Theremino PMT

Pulse amplifier adapted trom Theremino PMT

The counter, finaly, was made by an Arduino nano that drives the LCD and count the pulses incoming on the interrupt pin D2 on the falling side of the pulse. The source code is splitted in various images.

Library initialization, pin definitions
Global variables, custom characters definition
countPulse interupt funcion
Timers and display.