Project Idea :-  Water  Mixer  Controller  (Temperature)

A small, cheap, modular device to automatically adjust the mixing of hot and
cold water to produce a desired water temperature when a mixer valve is
opened.

Applications :-
Domestic - pre-set bath temperatures for babies, children and elderly,
pre-set dishwashing water temperature, pre-set washing machine
temperature(s), etc.
Industrial - car wash, process control, . . . actually lots and lots of auto
temperature applications, and not just for water (how about mixing hot and
cold fuel to the optimum injector temperature?).

Features :-
Powered by the temperature differential in the two input streams.
Controller easily replaced WITHOUT dismantling the tap (faucet for the
Americans)
Software to be fault tolerant, supply water temperature variation tolerant
and FAIL SAFE.

First Thoughts :-
* Powered by a thermopile (series of thermocouples) in the supply streams
feeding into a super cap. [Mounted semi-permanently in the tap]
* Input / Output monitoring by thermocouples.
* Output monitored by a small bellows which trips an over-ride spring if too
hot (re-set button required).
* Controls a solenoid by pwm through a H-bridge to drive it to any of
thousands of positions. The solenoid moves the middle plate in a ceramic
slide gate to control the mixing of the two streams. (Ceramic slide gates
have high friction, so will remain in place without needing the H-bridge to
hold the 'set' position) . [Mounted semi-permanently in the tap]
* PIC to monitor and control the whole system. [Mounted in a socket at the
rear of the tap]
* Long-life, rechargeable, low power battery built into PIC module.


Electronics Desired (whished for?) :-
A low voltage microcontroller with at least 2 analog inputs, 2 outputs
(operate the failsafe and to charge the battery) and a pwm H-bridge output.
Standby power source (battery), solenoid operating power source (thermopile)
and power storage device (super cap).


Any thoughts Piclisters ?

I can see a market for billions of these if it is possible to make them
cheaply enough.

Bye.

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