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HARDWARE.md

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Hardware

Bill of Materials

  • MCU: ESP32 Dev Board - see MCU.md
  • light sensor: BH1750 (BH1750FVI) in GY-302 kit
  • temperature sensor: BMP280 in HW-611 kit
  • 5x7cm double-sided prototype board, KYNAR wires
  • IDC10 board connector: 2x angled
  • IDC10 terminated ribbon cable to be routed at edge of window glass (so it can be behind shades), 3m
  • plastic case - Kradex Z34B

Light sensor selection

  • photoresistor: random accuracy, external ADC required
  • phototransistor TEMT6000: <570nm, external ADC required
  • BH1750: cheap, +/-20% accurate
  • TSL2581FN: more precise, but no ready-made integration, not easily available in reasonable package
  • TSL25911: seems the best, but not easily available at all

Cable selection

4 lines would be enough, but IDC10 is easier to obtain and is mure rigid. Future iterations may repurpose USB cable.

Schematic

Fritzing project: esp32-lightsensor.fzz

I2C

BMP280

Pulling CSB pin low will turn I2C off and activate SPI. On short wires I2C may be active even if CSB is left floating, but it really should be linked to VDD!

I2C address is 0x76 when SDO pin is pulled low or floating, pulling it high will switch it to 0x77. I2C address can be switched at any moment.

To set address in code, update following line in ../software/esp32-window-light-sensor.ino:

#define BMP280_I2C_ADDRESS 0x76

BH1750

I2C address is 0x23 when SDO pin is pulled low or floating, pulling it high will switch it to 0x5C.

To set address in code, update following line in ../software/esp32-window-light-sensor.ino:

#define BH1750_I2C_ADDRESS 0x23