water heater with temperature controller

[akg]

i don't think ur design is correct.
read the above proposed idea once gain.
the shift register should shift only when the counter overflows , and that is when the temp has not reached the desired level until 'N' pulses of 555 . If the temp has reached further counting of the counter should be inhibited (inhibition signal to 555 or to the counter itself )

 

[Paul Obrien]

The thermistor would have to be able to trigger and/or reset the 555, what happens if the temp is reached during the count.

 

[jemilsan]

My idea is when the desired temperature is reached, transistor Q2 will turn on and the current supplying the counter will go to ground thus basically turning the counter off.....Based on what I designed, am I right or not???

 

[jemilsan]

I have changed my design....

The idea is this.... the potentiometer R9 will set the desired temperature by limiting the current that will turn on the transistor Q2. The 555 timer, set at long intervals, will clock the shift register which will turn the heaters on.

Once the temperature is reached, transistor Q2 turns on and the voltage that supply the shift register will go to ground thus basically turning it off.

Pls. comment on the design.
Did I wire the shift register correct???? How do I wire it correctly??

 

[akg]

Did I wire the shift register correct????

u have wired the shiftreg in parallel in parallel out mode. all the heaters will be 'on' in the first time out

 

[jemilsan]

Please put an additional comments on my design.... it will help alot....
Tnx!!!!!

 

[Paul Obrien]

Don't forget to reset the shift register once the temp has been reached, or the next time there will be X + 1 burners come on instead of one burner

 

[SiriBrazil]

I would probably use a microcontroller for that kind of thing because it would be easy to modify the software for the purpose of adding features or improving the design etc. However, you could easily complete that project without a microcontroller and it sounds like this would be your best bet.

You'll need some form of temperature sensor for the front end of the project, and a sensor which converts temperature to a voltage would be ideal (there's loads of these on the market). You wouldn't need a linear sensor provided you're willing to add in some form of calibration so that the preset can be setup, although there are linear sensors out there which will convert a temperature, in degrees C or F to a voltage in a linear fashion. You'll want a comparator for the temperature sensor output, which will compare the temperature of the tank with your preset (a bias voltage on the other pin) and then make a decision at the output as to whether the tank is hot enough or not. Convert the output to a logic level so that, for example, not hot enough= logic0 and hot enough=logic1.

A 555 timer could monitor a time period and, via some simple logic control, a circuit could be designed which would check the temperature of the tanks compared to the preset at certain time periods. If, after one time period (the length of time of which would be set by the 555 timer), the tank was not hot enough, a second heater could be turned on. If, after 2 time periods the tank wasn't hot enough then a third heater could be turned on etc.

The tank heater control could simply be a decade counter which is incremented if the tank isn't hot enough, or even a simple binary counter with some decoding logic on the output.

I'm not going to design your project for you, because clearly that's your job - but I hope this has given you a few ideas to work with. I haven't given you a solution, but there are a few ideas there which should allow you to come to a solution yourself.

Let us know how you get on and, once you're a bit further into the design process maybe you can ask some more specific questions about how to tackle certain problems you're having.

Brian

Hi, Brian,

It's very interesting your sugestions to Jemilsam, and I have a similar problem, but more simple, I supose. I have one basic sink heater (for aquarium) and I would like to assemble a setable thermostat that turn the heater's power off when the preseted temperature was detected. I thougt to use a thermistor + SCR as a Triac trigger, and this, by your time, as the heater switch. I would like to know if (and how) it can be done using directly the 110 VAC, and leaving any DC power suply device. Do you know how can I do it?

Thanks.

SiriBrazil.