Using WDT as a Temp Sensor?

[modifyit]

Has anyone used the watchdog timer as a temp sensor per AN720?

http://ww1.microchip.com/downloads/e...tes/00720c.pdf

Just curious on the results and if this has been done using PBP. In the mean time I will start trying to write the code myself.

Thanks in advance,

[Archilochus]

Looks like an interesting project. The PBP code should not be difficult to write - remember to disable PBP's automatic watchdog timer clearing function (and then to clear the WDT as needed elsewhere in your code).

Calibrating the setup without a controlled temperature environment seems like it will be rough.
Some of the charts in the app note show a pretty bad deviation at around +30°C, not a good sign as far as reliability goes.

Also - Microchip says:

The linearity of the WDT is not guaranteed, but has been observed.

Not very encouraging. How about the TCxx series of temp sensors from Microchip instead?

Arch

[Acetronics2]

not worse than a using a NTC !!!

[Archilochus]

Was just thinking about this idea some more - couldn't this be used to calibrate PBP's 'SLEEP' and 'NAP' commands?

Arch

[modifyit]

How do I disable PBP autoclear of the WDT?

[modifyit]

Looks like DEFINE NO_CLRWDT is the command

[paul borgmeier]

Also see Melanie's post on getting the WDT to timeout even without the Define set.

@ goto $

http://www.picbasic.co.uk/forum/show...ight=no_clrwdt

I have not read the AN (yet) and am therfore not sure if this is helpful. It sounds like you could do some stuff in your program and then sit in a tight loop and count time outs ...

Paul Borgmeier
Salt Lake City, Utah.
USA