Electronic thermostat

In response to what Mike Steward posted in news: snipped-for-privacy@echo.uk.clara.net:

--
Joe Soap.
JUNK is stuff that you keep for 20 years,
then throw away a week before you need it.

Just the other day I saw a battery operated, indoor/outdoor thermometer for less than US$10.00. Not sure where I saw it; maybe at BG Micro (Garland, Texas). Don't remember whether or not it can read out in Celcius.

If I were doing it, I would use a microcontroller, an LCD, and a DalSemi/Maxim DS1820 or DS1822 digital thermometer "chip" (because I've used all of them before). As a matter of fact, several years ago I placed a DS1820 on the outlet pipe of my (natural gas) water heater and ran the wires - 20+ feet of twisted wire-wrap wire - to my livingroom, directly above, through an existing hole. :-) The DS1820 and 1822 chips report temperature in Celcius, so you'd be all set. (I wanted Fahrenheit, had to program the microntroller to convert.)

--
Michael

This sounds like the answer, any chance of a parts list and circuit diagram?

Many thanks Mike S.

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Texas).

DalSemi/Maxim

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hole.

all

I haven't a fancy diagram of the circuit but could scan a sketch and post that on alt.binaries.schematics.electronic. Circuit is not complicated.

Before I do that though, do you have a way to "burn" (program) a PIC? If not, my solution is useless to you, and you need read no further.

To give you an idea of cost, here's a list of major parts (excluding a few caps. and resistors): PIC16F84A OR PIC16F628A (I recommend the latter)

18-pin DIP socket 4.00 MHz crystal for the PIC Maxim/DalSemi DS1820 digital thermometer LCD display a 16-character, 1-line is sufficient 78L05 voltage regulator 6- OR 8- OR 10- OR 12v (AC OR DC) wall transformer (pick one)

Substitutions: A crystal oscillator could be used instead of a crystal. Any size LCD would work but a 1x16 is probably the cheapest.

--
Michael

I don't know how your tank is heated with a wood fire in a cupboard - heat exchanger?

I have an electric hot water heater I put a series of eight thermistors along the tank (no small task - had to take the metal cover and insulation off). The eight thermistors are spaced about five inches apart and epoxied to the tank.

They go to two quad comparators and are in a bridge circuit. The hottest water is at the top of the tank - where the outlet is and heats the fastest.

I turned the heater on from a cold start and allowed it to heat until both upper and lower heaters turned off. I set the reference voltage to the comparators so the LED's all turned on.

Now then the heater is running the LEDs come on from the top down - good to go for a shower when the first three are lit.

Seems to me you will only be measuring a small portion of the tank if you try to rely on a single measuring point. Water tends to stratify unless the convection currents can distribute the hot water evenly.

And I don't have a schematic - it was too easy.

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Take a look at this site for diagram. If you care to use a PC it also has software:

Dave