microcontrolled water heater controller

[lassy]

thermostamp.html

hi there!

I have been assigned a project whereby I have to
design a microcontroller based controller for a
domestic geyser/water heater.

basically the requirements of the controller is for
the user to be able to key in desired temp and on/off
times for the geyser.there should also be some kinda
fedback once the desired temp has been reached and an
alarm when the temp has exceeded a max temp setting.

please,if you can help,contact me!any help whatsoevre
would be greatly appreciated...even if its just some advice on which microcontroller and other devices to use because i have little to no knowlege on microcontrollers or how they work.can also email at lasborn@yahoo.co.uk

please help me!

thanks

 

[sztibi82]

Check this site:
**broken link removed**


you have to use only the R1, R2 and the 0.1uF condensator.
This will be supplyed by 5 V as in the schematic and the other terminal has to be entered into the analog in of a microcontroller.
The temperature regulator will be commanded using PWM, or depending which circuit you desire.

Tibi

 

[Munib]

for feedback u can use LM35 temperature sensor

 

[kentken]

Dalas Semi makes a nice stainless cased digital tempature sensor.

**broken link removed**

They work great and is easy to set up.

Kent

 

[Mr.Cool]

here are some key things to remember
- design for application (what are your requirements?)
- cost is everything. do not use a $3 temperature sensor, when a 50 cent version will work just as good.
- from a school point of view, it is better to build something that takes some thought than to copy/paste result.

some things to consider
- linearize your temperature sensor (if it needs it)
- use schmitt trigger with hystoresis for your temperature set points (you can software program the same effect if using a microcontroller)
- thermistors are cheap
- most of your cost will be because of the temperature probe itself. mounting it inside of a water tank + water proof will be tricky.
- Microchip makes the microcontrollers & also see their temperature sensors part number TC620

teachers love bells & whistles
- for ease of implementation and prototype, nothing beats the 1-wire interface for microcontroller applications
- also consider driving an LED or buzzer for two indications, water temp in Safe Operating Area or water temp is Over Temperature.
- on/off switch
- how can u make the quiesent current small?

Mr.Cool

 

[dannym]

If the heater is AC, you should not use PWM due to the noise it creates. You can use an SCR, probably optically isolated, or a solid state relay. The SCR has an additional benefit of proportional control rather than on/off, but it doesn't sound like you need that.

For the heater, you will also want to inhibit switching around the set point with a small amount of hysteresis or just a delay. Otherwise it could be set at 100F and at exactly 100F it would switch on and off, on and off as noise varies the ADC reading by a fraction of a degree.