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Homemade Radio Electronics
Atmel Mega88 Dual Temperatur meter

This project is made over a one week period of time, together with Simon and Benjamin 9th grade.

Design goal: to make a good accurate temperature meter, with data logging output using serial port 19200 Baud 8N1
Display one of the two temperature sensors on the LED display from -50 to +150C
Extra software task1: display "in" or "out" txt on the LED when selecting using the button.
Extra software task2: make display turn upside/down depending on signal input.
Extra software task3: increase readout resolution if selected by user, hold the button pressed for 4sec
Extra Extra hardware task: make a switch to indicate if unit is upside or not, for automatic display correction

First we made the schematic on the whiteboard, we made minor changes and added a few things later.

The pin out of the Microcontroller is important to know, the ports and what pin and so on.

Then we made a circuit board layout, only one layer needed, we got plenty of board space.
we printed it out, and etched and drilled and soldered.

Here the board with all components mounted.

Bottom side with soldering.

A and B are the RAW ADC values transferred from the temperature board,
C and C are converted into temperature using this formula: C=(A-99)*489)/1000 in excel.
This first curve we made is from cooling spray -40C to a cop of coffee +70C

The next curve is inside and outside temperatures during a fall night.

Things Learned:
Simple Electronics design with microcontroller, C programming, Debugging, Logging, data calculation and post filtering using excel,
Schematics, Printed circuit boards, soldering, power supply, heat, time constants, sensing.

We managed our goal all extra tasks compleeted and working, two units where made.

if you like try the HEX file here: softhex.zip
8MHz internal, no divide.

17th of November. 2006