Introduction
Build a 400V high-voltage power supply for a Geiger-Müller tube radiation detector with pulse counting and dose rate display. This comprehensive guide covers everything from design through implementation, testing, and deployment.
High Voltage Power Supply (Geiger Counter)
Build a 400V high-voltage power supply for a Geiger-Müller tube radiation detector with pulse counting and dose rate display.
DifficultyIntermediate
Duration2–3 weeks
Components10 items
Steps3 steps
Theory & Background
Geiger tube: sealed gas-filled cylinder (typically Neon + Halogen at low pressure). Central anode wire (+) surrounded by cathode cylinder. Bias voltage: 400–500V applied. Radiation passes through thin window, ionizes gas → ion avalanche (Townsend discharge) → current pulse detectable externally. Pulse duration: 100µs (recovery time). Quench gas (halogen) prevents continuous discharge (self-quenching). Output pulse: negative-going (~400V) pulse on anode — requires quench resistor (10MΩ) to limit current and voltage divider + coupling capacitor to create MCU-compatible 5V logic pulse.
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Components & Requirements
10 components required for this project.
| # | Component | Purpose | Qty |
|---|---|---|---|
| 1 | SBM-20 or J305 Geiger-Müller Tube | Radiation sensing element (beta/gamma) | x1 |
| 2 | MC34063 boost converter IC | 5V → 400V HV generation | x1 |
| 3 | High-voltage capacitor (0.1µF, 630V) | HV filter capacitor | x2 |
| 4 | Fast-recovery diode (1N4007 × 4) | Voltage multiplier rectifier | x4 |
| 5 | Voltage divider (1MΩ + 10kΩ) for HV sense | Safe HV measurement (÷100) | x1 |
| 6 | Arduino Nano | Pulse counting and display | x1 |
| 7 | OLED 0.96" display (I2C) | CPM, µSv/h display | x1 |
| 8 | Piezo buzzer | Radiation click sound | x1 |
| 9 | Interrupt input (100kΩ pull-up + 4.7kΩ quench) | Tube pulse detection | x1 |
| 10 | HV probe cable (for oscilloscope testing) | HV measurement safety | x1 |
Step-by-Step Implementation
Follow these 3 steps carefully.
1
Geiger-Müller Tube Operation
Geiger tube: sealed gas-filled cylinder (typically Neon + Halogen at low pressure). Central anode wire (+) surrounded by cathode cylinder. Bias voltage: 400–500V applied. Radiation passes through thin window, ionizes gas → ion avalanche (Townsend discharge) → current pulse detectable externally. Pulse duration: 100µs (recovery time). Quench gas (halogen) prevents continuous discharge (self-quenching). Output pulse: negative-going (~400V) pulse on anode — requires quench resistor (10MΩ) to limit current and voltage divider + coupling capacitor to create MCU-compatible 5V logic pulse.
2
400V Boost Converter Design
MC34063 boost converter driven at 50kHz. L1: custom wound on toroidal core (100µH). Switch: N-channel MOSFET (IRFZ44N). Diode: UF4007 (ultrafast, 1A, 1kV). Output: 400–500V adjusted by voltage divider feedback to MC34063 feedback pin. Voltage multiplier (Cockcroft-Walton): cascade of diodes and capacitors multiplies AC to higher DC. Alternative to single-stage boost — fewer inductor turns. Output ripple: typically 5–10V (measure with HV probe before connecting to GM tube). Safety: 400V at any current is lethal — treat all HV nodes with extreme respect.
3
Radiation Unit Conversion
CPM (Counts Per Minute): raw count rate — depends on tube size and sensitivity. µSv/h (microsieverts per hour): radiation dose rate — biological hazard unit. Conversion: manufacturer-specific. SBM-20: 1 µSv/h ≈ 175 CPM (for Cs-137 gamma). Background radiation: 0.1–0.3 µSv/h (10–50 CPM). Radiation sources: potassium in bananas (~0.01 µSv/h contact), smoke detector (Americium-241, low activity, ~0.01 µSv extra at contact), granite countertop, dental X-ray (50–100 µSv per image but brief). Alert levels: 1 µSv/h = elevated (investigate), 100 µSv/h = evacuate area immediately.
Code & Implementation
Core code for geiger_counter.ino:
geiger_counter.ino
C/C++
#include <Wire.h> #include <Adafruit_SSD1306.h> #define GEIGER_PIN 2 // Interrupt pin for GM tube pulses #define BUZZER_PIN 8 #define HV_SENSE_PIN A0 // Voltage divider output (HV/100) // SBM-20 tube conversion factor #define COUNTS_TO_USPH 0.00571f // 1 CPM = 0.00571 µSv/h volatile unsigned long pulse_count = 0; unsigned long last_count_time = 0; float dose_rate_usph = 0; float cpm = 0; // Interrupt: called on each Geiger pulse void IRAM_ATTR geiger_pulse() { pulse_count++; // Generate click sound on each radiation event static bool buzzer_state = false; digitalWrite(BUZZER_PIN, buzzer_state = !buzzer_state); } Adafruit_SSD1306 display(128, 64, &Wire, -1); void setup() { pinMode(GEIGER_PIN, INPUT_PULLUP); attachInterrupt(digitalPinToInterrupt(GEIGER_PIN), geiger_pulse, FALLING); pinMode(BUZZER_PIN, OUTPUT); display.begin(SSD1306_SWITCHCAPVCC, 0x3C); Serial.begin(9600); } void loop() { // Update every 10 seconds for stable reading if(millis() - last_count_time >= 10000) { unsigned long counts_10s = pulse_count; pulse_count = 0; last_count_time = millis(); cpm = counts_10s * 6.0f; // Scale to per-minute dose_rate_usph = cpm * COUNTS_TO_USPH; // Check HV level (should be ~400V, sense = 4.0V with /100 divider) float hv = analogRead(HV_SENSE_PIN) * 5.0f / 1023.0f * 100.0f; // ×100 for actual HV display.clearDisplay(); display.setTextSize(2); display.setTextColor(WHITE); display.setCursor(0, 0); display.print(dose_rate_usph, 3); display.print(" uSv"); display.setTextSize(1); display.setCursor(0, 20); display.print("CPM: "); display.print(cpm); display.setCursor(0, 35); display.print("HV: "); display.print(hv, 0); display.print("V"); display.setCursor(0, 50); if(dose_rate_usph < 0.5) display.print("Status: NORMAL"); else if(dose_rate_usph < 10) display.print("Status: ELEVATED"); else display.print("ALERT: HIGH RADIATION"); display.display(); Serial.print("CPM:"); Serial.print(cpm); Serial.print(" uSv/h:"); Serial.println(dose_rate_usph); } }Testing & Troubleshooting
Test High Voltage Power Supply (Geiger Counter) by verifying each subsystem individually before full integration.
Troubleshooting Tips
Verify power voltages, check ground connections, use serial monitor for debug.
Real-World Applications
Personal radiation monitoring in nuclear areas
Food and water contamination screening
Mine and geological radiation survey
Nuclear power plant safety monitoring
Medical physics radiation protection
Environmental radiation mapping
Educational nuclear physics demonstration
Emergency response radiation detection
Extensions & Next Steps
- Add GPS for radiation mapping (create radiation map overlaid on Google Maps)
- Implement energy spectrometry with NaI scintillator + PMT
- Build a beta/alpha/gamma discrimination circuit
- Add wireless data upload to RadTrack.me or global radiation monitoring network
- Design an SMT version with proper EMC shielding
Interactive Playground
Coming SoonAn interactive simulator will be available here — simulate circuits and run code in-browser without hardware.
Frequently Asked Questions
Is it safe to work with a Geiger counter and background radiation sources?
Background radiation: completely safe. Natural background (0.1–0.3 µSv/h) represents roughly 2–3 mSv/year — within normal variation across different locations. Calibration sources like small Americium-241 (smoke detector button: 1 µCi = 37,000 disintegrations/second) and Uranium glass: safe to handle briefly, don't inhale dust, don't ingest. High-voltage safety: the 400–500V in the Geiger counter power supply IS dangerous — can cause ventricular fibrillation. Keep HV nodes insulated and enclosed. Discharge capacitors before working inside. Never add more radiation sources without training — always verify dose rate with calibrated instrument first.
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