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The W5500's role is transformative: It converts a standalone analyzer into a networked IoT instrument—opening applications in remote monitoring, distributed sensor networks, and cloud-based radiation surveillance systems.

• STM32F407: High-speed ADC + DMA for gamma pulse measurement
• W5500 Ethernet: Real-time spectrum streaming to PC

This combination enables real-time analysis of hundreds to thousands of radiation events, displaying live gamma spectra on a PC screen.

1. System Concept – How a Gamma Spectrometer Works

Gamma rays are invisible, so they must be converted into energy values through the following stages:

① Scintillator — Gamma → Light

When gamma rays enter a crystal such as NaI(Tl), a brief light flash occurs. The brightness of the flash corresponds to the gamma-ray energy.

② PMT (Photomultiplier Tube) — Light → Voltage

Amplifies faint light by millions of times, resulting in an electrical pulse of several volts. Requires high voltage (500-1000V).

③ Analog Conditioning — Clean Pulse

Preamplifier + shaping amplifier refine the signal into a clean Gaussian pulse that the STM32 can read effectively.

Result: Each gamma-ray event is represented as a single pulse, where the peak height equals the gamma-ray energy.

2. STM32F407 – Ultra-Fast Pulse Processing Core

The performance of this project is determined by the STM32F4's 12-bit ADC + DMA + EXTI combination.

High-Speed Capture Pipeline

Amplifier Output → ADC (PA0) → DMA Circular Buffer → EXTI Trigger →  
Pulse Peak Detection → Histogram Binning

Technical Core: NDTR-Based Buffer Indexing Algorithm

The key challenge is locating where a newly arrived pulse resides in the DMA circular buffer. Using NDTR (Number of Data Transfer Remaining), the system:

• Immediately calculates pulse position
• Averages surrounding samples
• Accurately detects peaks

Before algorithm optimization: Spectrum peaks were blurred
After optimization: Very sharp energy peaks (experimentally validated)

Processing Speed: ~8 µs per event analysis

3. W5500 Ethernet – Turning It into an IoT Scientific Instrument

This spectrometer transcends a simple MCU project, expanding into a network-based real-time measurement device.

W5500's Role

• TCP/IP Offload: Minimizes MCU load
• Stable Streaming: Handles thousands of events per second
• Immediate PC Plotting: Ensures transmission speed for real-time visualization
• IoT Measurement: Enables networked instrumentation without OS or Linux

With W5500, the system becomes a complete Real-Time Radiation Spectrum Monitoring Device.

4. Real Measured Spectra (Actual Results)

Am-241 (Americium) – 59.5 keV Peak

• Two distinct low-energy peaks
• Exact match with theoretical values
• Validates proper MCA functionality

Lu₂O₃ (Natural Lutetium)

• Expected peaks: 202 keV, 307 keV
• Measured: Strong peak at ~200, secondary peak near ~300, similar 509 keV composite peak structure
• Matches characteristic pattern of natural lutetium samples

Uranyl Nitrate (Uranium Compound)

• Characteristics: Sharp peak in low-energy region, gradual distribution in mid-energy range, long tail structure
• Highly similar to typical spectrum of natural uranium compounds

Unknown "Anion Powder" Sample

• Results: Clear low-energy peak, multiple mid-range bumps, continuous tail
• Confirms presence of natural radioactivity
• Not a single isotope, but sufficient for "radioactive material presence detection"

5. Easy-F407V-ETH Board – Custom Hardware Design

The board is not just a development platform but a carefully designed experimental measurement instrument platform that harmonizes analog signal processing, high-speed MCU, and networking.

Why This Project Is Important

This project is a rare case that fuses two domains:

1) Professional-Grade Physics Experimental Equipment (Gamma-Ray Spectrometer)

• Actual isotope identification capability
• Real-time energy histogram generation

2) IoT-Based Real-Time Measurement (Streaming MCA)

• Networked instrumentation using W5500
• Remote monitoring and data collection capability
• Low-cost educational and research equipment fabrication

Conclusion

This project demonstrates the following:

✔ STM32F4's DMA + high-speed ADC alone can implement a professional MCA (spectrometer)

✔ Combined with W5500 Ethernet, it achieves functionality comparable to Networked Radiation Monitoring Devices used in research institutions

✔ Even with low-cost open hardware, it achieves scientific precision capable of properly distinguishing spectra of Am-241, Lu₂O₃, Uranium, and more

Final Summary

• IoT radiation analysis equipment ready for immediate use in education, research, and scientific experiments
• Validated project with clearly detected actual isotope spectra
• Engineering completeness with high-speed DMA + NDTR algorithm implementation
• Complete IoT measurement platform with W5500-based real-time streaming
• Rare-quality project that is low-cost DIY yet possesses professional functionality