“Since the war in Ukraine, the discussion about nuclear weapons raised and people got into thinking about radioactive exposure again. While there is no real fear, there is still some awareness and interest in the normal radiation levels you have around you all the time.
Every now and then you see a geiger counter project popping up in the web. Most of them look very solid and share their design files. However the least of them provide the measurements via WiFi. There are some, most of them not SMD but THT and thus are not very compact.
This was the starting point for a discussion with a friend and the journey of creating our own design.
But what do we need for an adequate geiger counter?
First of all: RGB LEDs!
No, just kidding. Of course the LEDs play some role in this design, but it’s certainly not the most important thing here.
We need a few WS2812 for creating some decent ambient lighting. Not just that, but also for signalling the current radiation level via its color.
When idle, the geiger tube shall glow in a decent green – or maybe cyan? You decide on your own, thanks to the RGB LEDs. When elevating a certain level, a warningly red glow signals something that hopefully won’t happen.
Also: Every count they shall light up with a bright white flash, to notify about beta particles or gamma rays passing through your tube.
That’s all great for the visual effects when showing off the counter, but will get a bit annoying if it is placed somewhere in the living room. So all of that must be configurable, down to making it dead dark.
There are various types of tubes which you might want to use in that kind of project. The most common tube is the SBM-20 which you can get for around 20-25 € on ebay. A great alternative would be the SBM-19, which is much more sensitive but also larger and a bit more expensive at around 40 €. Lately the prices went up, probably as the main sellers are located in ukraine or bulgaria.
I ordered SBM-20’s from both countries and both arrived, just the ukrainian one being a few weeks later. I initially didn’t notice that the seller was from ukraine and – to be honest – did not expect to arrive at all when I realized that. Great respect for the seller. Stay safe over there!
The heart: ESP32-PICO-D4
This is the far more important item. The brain is some proper state-of-the-art WiFi microcontroller with great bang-for-buck ratio. The ESP32 itself is already a nice piece, but the required external components makes you usually chose the WROVER or WROOM modules. While these are great and cheap, they still require precious PCB space.
For a while now, Espressif have their PICO series, which is the well-known ESP32 in a slightly bigger QFN48 7x7mm package, but with all required components integrated: The ESP32 core, a SPI flash chip and a crystal. So you just need the voltage supply and you’re ready to launch.
What does the ESP32 do in this design?
One task is to generate the PWM signal required for generating the high voltage. This is accomplished with a simple boost circuit, consisting of a 650 V N-Channel MOSFET, an inductor with 10 µH and a diode. Goal was to have a fully SMD design except the geiger müller tube. However the available inductors with 10 mH in SMD package have a quite high resistance somewhere in the 100 Ω ballpark, while the THT ones just have around 30 Ω. This greatly impacts the efficiency of the generator.”