GuruBlog

For my Raspberry PI based car-radio that lives in the housing of a blaupunkt radio from the sixties I needed to interface a variable resistor from my pi. Unfortunately the rapsberry pi has no ADC for the GPIO pins so I added a small ATTiny running the arduino-tiny firmware to read the analog values. The ATTiny is programmed as a I2C slave and is accessed in the same way as the radio part of the project.

you can find a tutorial on how to install and run the arduino-tiny firmware here

and you can find the I2C slave library for the attiny chips here

this is my day 18 project for 30daysofcreativity

This is the pythonscript that runs on the raspberry pi side to read the analog value from the attiny

import smbus
import time
bus = smbus.SMBus(1)

adr = 0x26

def swap( a ):
        return (a & 0xFF) << 0x8 | (a >> 0x8)

def write( chan, d ):
        bus.write_word_data( adr, chan, swap(d))

def read( chan ):
        tmp = bus.read_word_data( adr, chan )
        return swap( tmp )

bus.write_byte( adr, 1 );
a =  bus.read_byte( adr );
b =  bus.read_byte( adr );
print b * 256 + a

and this is the arduino sketch that runs on the ATTiny45

#include "TinyWireS.h" 
#define I2C_ADR 0x26

void setup() {
  TinyWireS.begin(I2C_ADR);
}

void loop() {
  byte byteRcvd = 0;
  if (TinyWireS.available()){
    byteRcvd = TinyWireS.receive();
    if ( byteRcvd == 1 ) {
      long a = analogRead(3);
      TinyWireS.send( (byte)(a & 0xFF));
      TinyWireS.send( (byte)(a & 0xFF00 / 256 ));
    }
  }
}