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LICENSE Initial commit Jan 7, 2016 Update Jan 8, 2016
attiny_photoresistor_i2c.fzz Code Jan 8, 2016
attiny_photoresistor_i2c.ino measurements are taken asynchronously from i2c requests Jan 13, 2016
attiny_photoresistor_i2c.png schematics Jan 7, 2016


Photoresistor connected by I2C using ATtiny85


This example shows how to build analog to digital converter using ATtiny85 and connect it to any device (Raspberry Pi, Arduino) using I2C bus. Here photoresistor has been used, but any analog meter will be fine: temperature, potentiometer, moisture...

#Reading data

ATtiny sends current measurement as 2 8bit value. First older bits, then younger 8 bits.

Wire.requestFrom(0x13, 2);    // request 2 bytes from slave device #0x13

int i =0;
unsigned int readout = 0;

while (Wire.available()) { // slave may send less than requested
byte c =; // receive a byte as character

if (i == 0) {
    readout = c;
} else {
    readout = readout << 8;
    readout = readout + c;




  • Notes

  • Arduino IDE 1.6.6. Should work on older releases, but never tested

  • Uses TinyWireS library. Get it using Library Manager of GitHub directly

  • ATtiny45/85 board definitions. Tested with damellis/attiny

  • Uses 1MHz internal osciallator

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