Random Channel Power Control Using MCU TRNG or PRNG for 3-Channel Device (STM32, ESP32, Relays, MOSFETs)

User question

How I can power on a random channel, supposing my device has three channel from 1 to 3?

Artificial Intelligence Response

Direct answer to the question

• Generate a random integer between 1 and 3 and map each value to one of the three power-enable lines (Channel 1, 2 or 3).
• Drive only the GPIO, relay, MOSFET or solid-state switch that corresponds to the selected number; keep the other two OFF.
• Reseed the random-number generator (RNG) at every power-up or trigger so the choice is not repetitive.

Detailed problem analysis

1. Functional blocks
   • Randomness source (pseudo- or true random).
   • Channel decoder (logic translating the random number to one of three “ON” lines).
   • Power switch (relay, MOSFET, SSR or analogue switch sized for the channel load).

2. Randomness generation
   a. Pseudo-Random (PRNG) in firmware
   – C: (rand() % 3) + 1; after srand(seed)
   – Python / CircuitPython: random.randint(1,3)
   – Better statistical quality: XorShift, LCG with proven parameters, or the MCU’s hardware RNG peripheral (e.g. HAL_RNG_GenerateRandomNumber() on STM32).
   b. Hardware True Random (TRNG)
   – Reverse-biased BJT/diode noise → AC-coupled → comparator → D-flip-flop → entropy conditioner.
   – Dedicated chips (Microchip ATSHA204, Maxim DS28E16) or on-chip blocks (e.g. RDRAND/ RDSEED on x86, TRNG on ESP32-S3).
   c. Human-timing method with logic ICs
   – 555 astable clocking CD4017; push-button gates the clock; stopping time is unpredictable to humans.

3. Channel decoding & switching
   – Three GPIO pins or three CD4017 outputs feed the gate/coil of the power switch.
   – Ensure only one path can be energised at a time (mutual exclusion):
   digitalWrite(CH1,LOW); digitalWrite(CH2,LOW); digitalWrite(CH3,LOW); then set chosen high.
   – For inductive loads add a fly-back diode or RC snubber.
   – Size MOSFET \(V_{DS}, ID, R{DS(on)}\) or relay contact ratings to exceed worst-case load.

4. Power-up and seeding
   – Use unconnected ADC channel, RC-timer value, or high-resolution counter of boot time as seed.
   – Store previous channel in non-volatile RAM if “no immediate repeats” is required; re-draw if same.

5. Timing and safety
   – Debounce mechanical buttons; allow settling time before energising load.
   – Respect any inter-channel dead-time demanded by the device (e.g., RF PA or high-power LEDs).

6. Verification
   – Functional: each channel energises correctly.
   – Statistical: χ² or Kolmogorov-Smirnov test over ≥1 000 activations; expect ~33 % each channel.
   – EMI / surge: check switching edges; add RC/LC filtering if needed.

Current information and trends

• Most modern MCUs (STM32 U5, ESP32-S3, Nordic nRF54) now embed AES-grade TRNGs: no extra parts.
• Low-RON smart high-side switches (Infineon PROFET, TI TPS27xx) replace relays in 12–24 V systems, simplifying channel control through logic-level inputs.
• Matter/Thread and BLE-mesh lighting nodes commonly randomise channel/scene selection for self-test and demo loops—the same principle applies.

Supporting explanations and details

• Modulo mapping: channel = (rand_val % 3) + 1 guarantees 1-3 inclusive even if RNG width changes.
• Weighted selection: use cumulative probability table if Channel 3 must be twice as likely, etc.
• Analogy: think of a rotary switch with three positions spun at random, then latched. The microcontroller emulates the hand that spins it.

Ethical and legal aspects

• UL/IEC safety: switching mains or >60 Vdc requires reinforced isolation; opto-isolated SSR or relay.
• EMC compliance: ensure conducted and radiated emissions meet CISPR 22/EN 55032 if marketing the device.
• Security: if the random channel controls secure resources (e.g., test jig with proprietary firmware), use TRNG to avoid predictability that might be exploited.

Practical guidelines

1. Choose a controller with built-in TRNG if available; else seed a PRNG properly.
2. Keep control ground common with power switch source unless optical isolation is used.

3. Code skeleton (C – MCU with HAL):

   void select_random_channel(void)
   {
   uint32_t rnd;
   HAL_RNG_GenerateRandomNumber(&hrng,&rnd); // TRNG
   uint8_t ch = (rnd % 3) + 1;
   HAL_GPIO_WritePin(CH1_GPIO_Port, CH1_Pin, GPIO_PIN_RESET);
   HAL_GPIO_WritePin(CH2_GPIO_Port, CH2_Pin, GPIO_PIN_RESET);
   HAL_GPIO_WritePin(CH3_GPIO_Port, CH3_Pin, GPIO_PIN_RESET);
   switch (ch){
   case 1: HAL_GPIO_WritePin(CH1_GPIO_Port, CH1_Pin, GPIO_PIN_SET); break;
   case 2: HAL_GPIO_WritePin(CH2_GPIO_Port, CH2_Pin, GPIO_PIN_SET); break;
   case 3: HAL_GPIO_WritePin(CH3_GPIO_Port, CH3_Pin, GPIO_PIN_SET); break;
   }
   }

4. Bench-test with electronic load; log selections to PC to validate distribution.

Possible disclaimers or additional notes

• If the channels are RF frequencies, not power lines, substitute “enable pin” with “PLL/mixer path select”.
• High inrush loads (cap-input PSUs, LED strips) may require soft-start circuitry.

Suggestions for further research

• Evaluate NIST SP 800-90B entropy estimation if the system is security-sensitive.
• Look into deterministic random bit generators (DRBG) embedded in modern MCUs for FIPS-compliant systems.
• Explore ISO 7637-2 transient immunity if switching in vehicle electrical systems.

Brief summary

Select a random integer 1-3 with a well-seeded RNG (preferably TRNG), map that value to a single power-switch control line, and ensure mutual-exclusive activation. Size the switch for the load, add fly-back or snubber protection, and validate statistical uniformity and electrical safety.

Disclaimer: The responses provided by artificial intelligence (language model) may be inaccurate and misleading. Elektroda is not responsible for the accuracy, reliability, or completeness of the presented information. All responses should be verified by the user.