A very simple project

Page last updated 15 Dec 2009, by Allan Newton. 2 replies

This simple project measures temperatures and writes date, time and temperature to the PC

 

The sensor is the National SemiConductor LM35, a three terminal device with an analogue output of 10mV/°C

Connecting the LM35 is simple, connect the Vs to pin 29, Gnd to pin 0 and Vout to pin 20.

Make pin 20 an anaolgue input in the code and simply measure Vout from the LM35.

I measure the voltage as a floating point variable which needs to be multiplied by 3.3 to give the input in volts then by 100 to give a temperature in °C

Most of my code is taken up with setting the clock, soemthing which will become redundant once I get my battery backup working.

The only two lines that count are


AnalogIn ain(p20);

temp = ain.read() *330 ;

2 comments

Jan Mulders
21 Apr 2010

Tried this and it works great! You'll need to put a 1uF capacitor on your supply line though, as the ripple of powering it from USB can cause some seriously unstable results.

My temperature graph can be found here: http://timetric.com/series/01o0bfLGTgywBcYiCqxJ8Q/

In addition, it seems as though the setup I have measures temperatures about 5-6'c higher than they actually are. This seems to be down to the LM35 producing a voltage too high (0.33v at 24'c). I will investigate further.

ITII ITII
22 Apr 2010

Nice project, you could make a more tutorials stating from this one to a huge project like a plane ! Ok maybe not a plane but a bigger project.

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