Temperature controlled timer

[Marshiewoo]

Heya,

I am looking to make a Temperature controlled timer, Being that when the device goes above -16°C then a timer starts counting down from 30 minutes. Then when it goes back to below -16°C the timer restarts and stops, awaiting it to go back higher than -16°C.

I am wondering how I can do this, what chips and power I will need, and if somebody could point out where I can get all of the components from, maybe even sketch out a quick and simple picture for me?

I would be really thankful for anybody that can help me out.

Thanks,
Marshall Wade

 

[crutschow]

It would help to know what you are trying to control with this timer. That will determine some of the components.

Do you need an indication of the countdown time?

How much difference is there between "above -16°C" and "below -16°C"?

 

[Marshiewoo]

Yes I would like it to be displayed on a small segment screen.

There is a rather big difference, it is to tell if the device is inside a freezer or outside a freezer.

 

[Marshiewoo]

To add more info, I would just like a timer to go from 30 minutes to 0 on a screen when the device is taken out of a freezer. When it is back in the freezer, the timer will be reset and stopped.

 

[Marshiewoo]

Not what you wanted?

 

[cobra1]

are you wanting this made or do you want to make it yourself??

 

[Marshiewoo]

I would like it to be made originally by myself for testing and display purposes and after that I would probably get it manufactured.

 

[crutschow]

If you are looking for something cheap to manufacture then it would probably be best to use a microcontroller with a built in A/D converter to interface with the temp sensor, and an LCD driver to interface with the display. I'm not familiar with specific devices but here's some PIC units with a direct LCD interface (check the Graphical Display column).

 

[MikeMl]

Even better, use a TI MSP430Fxxx with a built in A/D and direct LCD drive. Using these, it is possible to make battery-powered instruments that run on small batteries for a Verrrry long time...

 

[Jon Chandler]

This might be a good starting point for you, using Swordfish Basic. The circuit uses a PIC18F micro and a low cost temperature sensor. Adding a display would be pretty simple.

There's a lot of other useful information and examples on the site too.

 

[Diver300]

I suggest one of the digital temperatures sensors like the DS18B20 or the LM74. Then you don't have to worry about analog accuracy.

LCD screens can stop working at low temperatures, so that is worth checking.

 

[Marshiewoo]

Thanks very much guys! I will check all of your suggestions out

Marshall Wade