[tech] temperature logging

Davyd Madeley davyd at ucc.gu.uwa.edu.au
Sun Jul 10 16:54:49 WST 2005


I acquired a serial I/O board on loan from work (will have to buy
them a new one). This board offers 8 bits of digital I/O and two 8
bit ADCs.

One of these ADCs is now connected to a thermal sensing
semiconductor. The board is connected via RS-232 to Centipede, the
DECserver in the tall rack.

To read the temperature:
 llogin THERMAL			<-- connect to the board over LAT
 rd0				<-- read port 0
  (the decimal representation of a byte will be displayed, close the
   connection - ^] on mussel)
 dc				<-- everyone's favourite calculator
 $reading 139 - 0.512 / p
  (prints the temperature in celsius)

It's only accurate to about 2 deg C according to the appropriate
datasheets, so the decimal places aren't that important.

It's currently connected using an Eric, because I couldn't find
enough appropriate serial to connect it, specifically a DB-9 gender
bender. It's also connected to a 9V plugpack via a 110V stepdown
transformer, as I couldn't find a 9V pack designed for Australian
voltages.

If we want, it would be very easy to tie the door sensors into this
thing using some 10k resistors (to stop the inputs floating). It can
also provide enough current to drive a solid state relay (for the
door lock) and has another ADC, if we wanted a second temperature
sensor.

The machine room is a pleasant 35C at the moment. This has not been
tested against another thermometer.

--d


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