binder@asd.DEC.COM (NOW willya gimme some fightin' room?) (11/03/86)
> Has anyone added thermometers to an Apple ? > > Keith R. Stanley > decvax!ihnp4!ihlpa!krstan asks: The easiest and by far the cheapest way to do it is to use a couple of thermistors wired to the game port. For each thermometer, use a thermistor of about 100K max resistance. Wire one end of the thermistor through a 27K resistor to +5V and the other end to a 27K resistor that goes to one the game port's paddle inputs. This will give a resistance range from about 54K to 154K - a good match for the 150K potentiometer that is used in Apple paddles. To calibrate, put the thermistor in a bowl of ice water - that's 32F or 0C. Read the paddle and note the reading. Put the thermistor in a pan of boiling water - that's 212F or 100C. Read the paddle and note the reading. (If you're at a very high altitude, find an accurate thermometer to tell you what the freezing and boiling temperatures really are.) When you're calibrating, make sure the circuit includes all the wire that will be used when the thermistors are in place, to avoid inaccuracies introduced by long wires. Thermistors are pretty linear, so you can write a simple scaling program in BASIC to calculate temperature from the paddle reading. Put one indoors and one outdoors (protected from the wind and rain) and you're all set. Cheers, Dick Binder (The Stainless Steel Rat) DEC Enet: ASD::BINDER UUCP: { decvax, allegra, ucbvax... }!decwrl!asd.dec.com!binder ARPA: binder%asd.DEC@decwrl.ARPA