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Technical Documentation - Explore  Prototype Developer Online

A deep dive into the materials, logic, and problem-solving strategies employed during the prototype construction and testing phases.

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Logic Implementation

The Pseudocode (Human-Readable Logic):
 
1. INITIALIZE: Connect to Wi-Fi and start the Cloud sync.
2. SENSE: Read internal chamber temperature (t).
3. EVALUATE: Is t ≥ 26.0°C ?
4. ACT: > * IF YES: Click Relay ON, Spin Fan, Light RED LED, Display [COOLING].

  • IF NO: Click Relay OFF, Stop Fan, Light GREEN LED, Display [SAFE].
    5. TELEMETRY: Send t to ThingSpeak Cloud.

    6. CYCLE: Wait 20 seconds and repeat.

Hardware & Tools

Troubleshooting & Redesign

Logic Inversion (The "Fan Always On" Bug)

  • The Issue: We initially programmed the relay to turn ON when the signal was HIGH. However, our relay module was "Active Low," meaning the fan stayed on when the temperature was safe.
     

  • The Fix: We performed a Logic Calibration in the firmware, swapping the HIGH and LOW commands to match the relay’s physical trigger requirements.

LCD Power "Brown-out"

  • The Issue: When the fan and LCD were powered from the NodeMCU’s 3.3V pin, the LCD screen became too dim to read, and the Wi-Fi would disconnect.
     

  • The Fix: We redesigned the power rail to use the VIN pin (5V) for the LCD and Relay, ensuring they received full power from the USB source without taxing the microcontroller's 3.3V regulator.

Evaporation Saturation (The Burlap Redesign)

  • The Issue: The sand alone didn't transfer moisture to the inner pot surface quickly enough for rapid cooling.
     

  • The Fix: We introduced a Burlap Wicking Layer wrapped around the outside wall of the inner pot. This acted as a "moisture bridge," ensuring the entire surface area stayed wet for maximum evaporative efficiency.

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