Car thermometer with voltmeter function

[Vermes]

The main function of this device is to measure the temperature of gas installation evaporator and the engine intake air temperature.
Main assumptions:

1. displaying 3 temperatures
2. monitoring the voltage of car gas installation
3. adjustable LCD backlight
4. Small hosting
5. Easy temperature sensor connection

Schema:



The main elements of the circuit:

1. Atmega8
2. Alphanumerical LCD display 2x16
3. 3 x DS18B20 (temperature sensor)

The PCB's:



After installation:



On the picture above there are two cables:

1. One cable to the car ignition
2. And the second one to parallel connect temperature DS18B20 sensors

The program is written in C.
The main function what were implemented:

• detection of number of 1 wire devices connected
• induction and activation of one of the few 1 wire systems connected to the bus
• temperature reading from a selected sensor
• measurement resolution to 0.5 degrees (view to 1 degree)
• displaying '-' for negative temperatures
• ability to enable of disable the '-' sign
• saving the display order form 1 wire sensors (saved in EEPROM)
• voltage measurement to 0,1V
• averaging rapid voltage changes (it gives a stable reference in case of small voltage fluctuations)
• function displaying “staring voltage” - the minimal voltage during engine start
• PWM LCD backlight control

Link to original thread - Termometr samochodowy z funkcją woltomierza