attiny-obd

Display OBD statistics on a 16x2 LCD display using an attiny85.

This project hijacks the tx and rx serial lines on a conventional ELM327 OBD interface device to send and retreive data. This data is then displayed in a nice format on an LCD1602 via i2c.

Compiling and programming

An AVR programmer of choice can be used to program the attiny85, however a really easy way to achieve this is by using a spare raspberry pi as an SPI programmer. See the following blog post by Kevin Cuzner on how to set this up:

https://web.archive.org/web/20220629132626/http://kevincuzner.com/2013/05/27/raspberry-pi-as-an-avr-programmer/

Assuming that the linuxspi programmer is being used on a raspberry pi, the steps are:

Configure the linuxspi programmer

The linuxspi programmer has a reset function that can drive the reset pin on the AVR device low to enable SPI programming. To enable this feature the following config should be placed at /root/.avrduderc:

programmer
  id = "linuxspi";
  desc = "Use Linux SPI device in /dev/spidev*";
  type = "linuxspi";
  reset = 22;
;

Connect Raspberry pi to attiny85

The following pinout should be followed:

Rasp pi	attiny85
GPIO 22	PB5
GPIO 10	PB0
GPIO 09	PB1
GPIO 11	PB2

Configure the fuses on the device

The following changes need made to the stock fuse configuration for the attiny85 to run avr-obd:

Clock divider bit CKDIV8 unset, this allows the attiny85 to run at 8Mhz
Brown-out detection bits BODLEVEL[2:0] set to 4.3v, this prevents the 3.3v TX and RX lines of the ELM327 from powering the device

The following avrdude command will set the correct bits on the fuses:

sudo avrdude -p t85 -P /dev/spidev0.0 -c linuxspi -b 30000 -U lfuse:w:0x62:m -U hfuse:w:0xdc:m -U efuse:w:0xff:m

Fuse values calculated using Fuse Calculator.

Run the Makefile

The makefile will build each *.c file under src/ and then link them, it can also call avrdude to perform the spi copy.