Getting a digital value into your BBC to represent the temperature of some physical object is made simplicity itself by attaching a ready made board to your Beeb. Before, the alternative approach would be to use the analogue port to read from a thermistor of similar device - but which would be hard to calibrate.
This module allows temperature data to be shifted into the BBC as a background task, while you continue to use the machine for another purpose. This could be of use in (for example) a shop, where the BBC was used for stocktaking while also monitoring (and saving) the temperature of chillers for hygiene reasons. Or monitoring the temperature of your green house while typing a letter to your aunt!
Parts
The circuit diagram shows electrically how to assemble the unit. It requires the following parts:
1
x
Ready built module (Maplin order code: FE33L9x ZTX300 NPN switching transistors)
9
x
10k pull up resistors
9
x
1.2k base resistors
In addition, it may be useful to have a handful of pins, a user port plug and a couple of feet of ribbon cable.
Benefits
Software-selectable sample rate, mode, and hi/lo point
Runs off a single AA battery
Choice of Celsius or Fahrenheit
Separate 'hi alarm point reached' and 'lo alarm point reached' pins
Build
Join from the pre-made module to your board with a short length of 14 way ribbon cable, noting which wire is ground.
Attach the resistors and transistors from the output from the BBC User Port to the control lines on the module. The REM statements at the start of the software and the hints section below tell you which is which. Note PB7 was not needed.
Do the same again in the opposite manner for the data and clock inputs from the temperature module back into the BBC's interrupt lines, CB1 and CB2.
Ensure that both 0v lines on the BBC and temperature module are joined together.
Hints
You might want to add a three small (1.5v) piezo buzzers to the alarm point pins, pin 6, 7 and 15. Otherwise, just leave them unconnected. Ground is pin 1.
The software can easily be modified if you made a mistake wiring up the pins though I suggest:
1st August 1998