[Homemade Quantum Computer NMRQCP] How to Control a Battery (12V) with a Microcontroller (3.3V)?

*Original Japanese version is available here.

 Hello! I'm a KOSEN student taking on the challenge of developing a quantum computer using a homemade Earth's Field NMR (EFNMR) system.

This time, I'm sharing scenes from the "high-current switching" test, which is the cornerstone of hardware control. I will explain the techniques for safely manipulating huge currents using the tiny amount of power from a microcontroller!

How to Control a Battery (12V) with a Microcontroller (3.3V)?

In my project, to completely prevent noise contamination from wall outlets, I am using a 12V fully sealed lead-acid battery (12V12Ah WP12-12) as the main power supply for polarization.

However, the pins of the microcontroller controlling this, the "M5Stack CoreS3 Lite," can only output a very weak 3.3V signal. If this signal is connected directly to a high-current circuit, the microcontroller will instantly blow smoke and break.

Therefore, I designed a drive circuit using an N-ch power MOSFET "2SK4017(Q) (60V5A)" as an "electronic switch" to safely and accurately turn the 12V high current ON and OFF (switching) using the tiny signals from the M5Stack.

Operation Test on a Breadboard and Oscilloscope Waveforms

First, before connecting the real coil, I built a test circuit on a breadboard (EIC-102BJ) using a dummy load (LEDs and resistors).

I sent a pulse signal from the M5Stack and used a portable oscilloscope to check the switching waveform to see if the MOSFET was turning on and off properly.

The result was a huge success! I was able to confirm that the MOSFET reacted normally to the signal from the M5Stack, and the expected switching waveform was being output.

💡 Impressions of the oscilloscope waveform
The rise and fall times of the waveform were extremely sharp, switching cleanly. At the dummy load (LED) stage, there was almost no noticeable noise or waveform distortion (ringing), resulting in very clean switching.

The Next Challenge: The Terror of "Surge Voltage"

The low-current test using LEDs was perfect, but I can't let my guard down. In the real setup, I will connect my homemade giant polarization coil (wound with 2UEW enamel wire) here.

The coil has a "huge inductance component (a property that resists changes in current)." The moment a large current is suddenly cut off, the coil forcefully tries to keep the current flowing, generating a powerful back electromotive force (surge voltage). If you do this without any countermeasures, there is a high risk that the MOSFET will be destroyed in a single blow.

For the actual implementation, I plan to build a reliable surge protection circuit by inserting a "Fast Recovery Diode 20NFA40 (400V2A)", which I have already procured, in parallel with the coil as a freewheeling diode.

Hardware development is a battle against these "risks of destruction," but the joy when a circuit works exactly as intended is exceptional!

• Daily experiment notes and code: Available on my GitHub repository (nmr-qc-project)
  
• Real-time development scenes and oscilloscope waveforms: Posting on X (formerly Twitter)
  

If you are wondering things like "Will it really work?" or "How do you generate waveforms?", please bookmark this blog and follow me on X!