/dev/coffee (was Re: Plants as network medium?)

force force at zip.com.au
Thu Sep 3 06:16:19 EST 1998


Ross Crawford (rossc at prologic.com.au) wrote:
: 
: Hey, that's interesting. Some guys where I work (inc. me) were looking at
: putting together a sensor on our urn and interfacing it (probably thru a
: games port) to our intranet web page, so we know when it's at the optimum
: temperature to make a cuppa. Hasn't got very far. What's the best device to
: use? Thermistor? We're not looking at high accuracy. Just a rough idea.
: Needless to say, the less $$$ involved, the better. 8?)

Get a thermistor and place it on the urn, as the temperature goes up the 
resistance of the thermister changes, hook it up to a known voltage source
and watch the voltage change as the temperature changes. Then get get a 
little digital multimeter whcih can interface with your PC and read the
values off that :)

I've built one that hooks up to the parallel port. You just need an A/D,
a voltage divider circuit and a few other bits and pieces. If you have
a bidirectional parallel port you can also dispense with the MUX thats 
usually used in such a circuit.

Below is what you'll need to set it all up. with (V) being the voltmeter
you'll make :).. All up, it should cost you about $30USD and a bit of 
time :)

             |----(V)----|
             |           |
 |--------------\/\/\/\/----|
---                         |
 -                          |
 |__________________________|

Cheers.
-- 




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