Introduction: W-GM Count - IoT (Wifi) for Radioactivity Monitoring

By
Status: Version 1.1
Date : Dec. 2018
Status : Beta
Difficulty : Low
Prerequisite : Electronics
Documentation : Read the PDF
Support : Forum only, no PM


The W-GM Counter based on an ESP32 chipset (Heltec WIFI kit-32 with OLED) is a fork of the Ethernet C-GM Counter and costs (27$/22€) about half price of the C-GM Counter.


This D.I.Y low cost radioactivity counter project provides hardware and firmware for building a Geiger-Müller counter device aka G.M. counter for continuous measurement of the radioactivity level. It is uses an ESP-32 with OLED, a booster module inside the 400V power supply, a battery charging circuit and very few components around.

Our design has been drastically optimized to reduce as much as possible to the minimum number of components and enable users to wire the hardware on a piece of Veroboard without requiring specific material.

The W-GM Counter is able to run as a standalone radioactivity counter or for ensuring long term radioactivity monitoring, can be used in association with A-GM Manager (see the Eco-System) that is an open-source web application running on a SOHO server (e.g. QNAP sells Small Office Home Office servers). A-GM Manager is also able to publish the W-GM Counter measures on the worldwide shared map managed by GMC MAP. Finally, there is also a Node-RED version for integration of the W-GM Counter with Node-RED such as the QNAP IoT framework.

NOTE: The W-GM Count uses fragile components that can be easily destroyed and makes it assembly a little more complex. You have been warned! During the development, I had one ESP8622 destroyed while powered by a DC pack on USB and one Heltec ESP-32 Wifi Kit-32 out-of-order due to 3V3 failures with no clear reason. This will drastically increase the final cost of the DIY device. I cannot be blame for this.


IMPORTANT (risk of electrical shocks)

The device requires a 400 Volts power supply. Despite the current delivered will remain very low, I discourage people not accustomed dealing with electronics and electricity to try building this device but to choose a commercial product instead (see available compatible products in the Eco-system section).

Step 1: The W-GM Counter Device

FEATURES

  • Radiation detection types: beta, gamma, X-ray
  • Detector: Geiger-Müller tube STS-5 / SBM-20 (400 V)
  • Maximum values: 65535 CPM / 425 µSv/h (theoretical)
  • Display: OLED dot matrix 132x64
  • Keyboard: 1 tack switch
  • Sound: Buzzer piezo
  • Indicator: LED white
  • Connectivity:
    • USB
    • WIFI 802.11b/g/n, DHCP only
  • Interface language: English only
  • Dimensions: W : 100mm x H: 60mm x D: 25mm
  • Weight: ca 95g w/o cables and power supply
  • Power supply: 5V USB DC pack / 2 Watts
  • Accessories: USB cable, 5V DC pack

Step 2: Building the W-GM Counter

Short description

See the PDF file for details


HARDWARE

The MT3608 module is a DC-DC Step-up (booster) able to deliver up to 2A with a 28V maximum output voltage. The input voltage can be set between 2V and 24V. In our design, we use the battery output (3.6-4.2V). The step-up will be adjusted for providing a 27V output voltage. This module ensures having a very stable voltage within the range of the battery voltage. Moreover it steps up the voltage to be used for the high voltage power supply.

The high voltage power supply is made of a switcher (IRF840) that hashes the 27V and increases the voltage up to 400-450V. The MOSFET IRF840 is driven by the PWM (Pulse Wide Modulation) signal delivered by the ESP32 at about 4 kHz. The PWM duty cycle must be adjusted to enable the current in the self to provide overvoltage when cut-off. The diode and capacitance rectify and increase the high voltage. HV capacitance must support at least 1kV. The R4 is made of two 4M7 and the power to dissipate is 68mW.

The use of a TP4506 module for charging the battery was motivated after the destruction of ESP32/ESP8266 module CP2102 USB converters while powered by a 5V DC pack. Therefore we have decided to not use the micro-USB for powering the device and neither its battery charging circuitry. The TP4506 module has been added to enable the battery charging and device powering. The battery can be charged from a DC pack whereas the power switch is off. According to the battery capacity, the RProg resistor on the TP4506 module must be changed (see the Battery Charging Current Setup section).

Revision 1.1
We have modify the power switch to insulate the battery because the TP4056 drains about 3µA when the device is off. The LIPO battery voltage was dropping below 3.2V causing problems. The counterpart is the need to always power on the device for charging the battery.

STORAGE : for long period of inactivity, we strongly recommand to fully charge and disconnect the Lipo battery before storage.


SOFTWARE

The W-GM Counter Device programming can be done using the W-GM Counter device BIN file and the Flash Download Tools utility. The “Flash Download Tools” application can be downloaded from the Espressif website at .

  • W-GM_x.x.bin Use this to download the firmware into the ESP-32 chipset.

Attachments

Step 3: Using the W-GM Counter

Short description

Please read the PDF for details

The W-GM Counter device counts the number of radiation pulses (CPM) over a one minute period (shifting window), and convert this count into a micro Sievert per hour (µSv/h) value using the G.M. tube conversion factor.

  • At start-up, the splash screen displays the version and copyrights of the C-GM counter device firmware.
  • About 5 seconds after the power-up, the splash screen closes and the counter starts the radiation measurement.

The user interface was made very simple and there is only one tack switch for control the device screens and menu.

According to the duration of the button push, there are two possible actions.

  1. Short press = SELECT User press the button less than half second.
  2. Long press = NEXT User press the button more than half second.

To ENTER the Menu or validate a menu entry, make one long press.

To Jump to next screen or menu entry, make one short press.

There are 6 information screens:

  1. RADIATION SCREEN
  2. DETAILS SCREEN
  3. DOSIMETER SCREEN
  4. PARAMETERS SCREEN
  5. NETWORK SCREEN
  6. CREDITS SCREEN


CONFIGURATION MENU

There are 6 menus screens for configuring the device. Some parameters must be set using the communication ports (Serial or Network).


ElectroSmog (magnetic fields)

Persons subject to electro-sensitivity (ElectroSmog) shall understand that the self used in the High Voltage design does not completely close its fields and there are some magnetic/electrical field leakages very close to the device (about 0.5µT and 1300V/m when touching the casing, but no more significant and far below SBM-2015 recommandations at 5cm)