Electronic thermostat

[Mike Steward]

I am looking for a cheap method of fitting some sort of thermometer to my
hot water tank which is heated from a log fire. The tank is built in to a
cupboard and very well insulated, therefore difficult to get at. I need
ideally some sort of digital read out in centigrade 0 to 100 deg.

The sensor would have to be on a cable about a metre long.

Any ideas ? Mike S.

 

[Joe Soap]

I am looking for a cheap method of fitting some sort of thermometer to my
hot water tank which is heated from a log fire. The tank is built in to a
cupboard and very well insulated, therefore difficult to get at. I need
ideally some sort of digital read out in centigrade 0 to 100 deg.

The sensor would have to be on a cable about a metre long.

Any ideas ? Mike S.

http://cgi.ebay.co.uk/Wireless-Thermometer-By-PINPOINT-New-
Warranty_W0QQitemZ7753981845QQcategoryZ20758QQrdZ1QQcmdZViewItem

 

[Michael]

I am looking for a cheap method of fitting some sort of thermometer to my
hot water tank which is heated from a log fire. The tank is built in to a
cupboard and very well insulated, therefore difficult to get at. I need
ideally some sort of digital read out in centigrade 0 to 100 deg.

The sensor would have to be on a cable about a metre long.

Any ideas ? Mike S.

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.)

 

[Mike Steward]

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

Many thanks
Mike S.

 

[Michael]

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

Many thanks
Mike S.

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.

 

[default]

I am looking for a cheap method of fitting some sort of thermometer to my
hot water tank which is heated from a log fire. The tank is built in to a
cupboard and very well insulated, therefore difficult to get at. I need
ideally some sort of digital read out in centigrade 0 to 100 deg.

The sensor would have to be on a cable about a metre long.

Any ideas ? Mike S.

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.

 

[CheapscateDave]

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

Many thanks
Mike S.

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

http://www.elektroniikka.org/thermometer/

Dave