chip crash

[ideasman]

HI All'
Can some one give me a solution.
Im doing some uart commands turning relays on and off which works and after 5mins or so the chip freezes. After a hard reset it goes again, can some one tell me why and how to amend this.

cheers
ideasman

[peterverkaik]

Do you use a transistor or (mos)fet to switch the relays?
The I/O pins are not suited to drive relays directly.
Also. do you have a diode to suppress
emf voltages when you switch relay off?

regards peter

[ideasman]

yes I am using a transistor, no driving directly I am using optocouplers and yes all suppressed with a diode.
It has something to do with data in the buffer/stack it chokes on the data after sometime?

Thanks but I dont think thats it.

ideasman

[ideasman]

I think I have found the problem but I need a solution if someone knows of one.

Im using a 4-20ma loop un isolated as a test I am heating a cup of water at 85C and keeping it there and I am getting galvanic problems from the probe via the heating element so when the water gets hot I get better electron flow in the water and my thermo amp AD595 goes hard on and basically lights up the RBO input(analog input) jamming the micro until it disipates the energy in the water or somtimes it just jams.

My question is does anyone know how to isloate the stray noise for a thermcouple circiut. For the time being I have put the probe in an electrostatic bag and the chip is working a lot better but this is not a solution only a bandaid one.
Are there isolated themocouples or is it an isolation IC job?

Cheers
ideasman