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[Moved] thermocouple and lcd

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mohamed.elsabagh

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I have a problem and i need help in it. I have a system contains a circuit contains microcontroller and some other components connected to a thermocouple, and lcd which shows the temperature read by the thermocouple.

Now the problem is when the thermocouple moves on a surface like pcb or something for sometime the lcd shows some strange characters on the lcd or it doesn't show anything at all, but when the microcontroller is reset every thing goes to normal. what might be the cause of the problem? the software driver may have a problem??or what else?
 

do you design the instrumentation first?

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do you design the instrumentation first?
 

Magvitron said:
what you mean by the thermocouple moving on pcb??
Click to expand...

I mean the thermocouple keeps touching the pcb and i move it on random motion, maybe this motion generates some elctro static charges i am not sure

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madhusuthanan said:
do you design the instrumentation first?

- - - Updated - - -

do you design the instrumentation first?
Click to expand...

what do you mean? I didn't understand your question clearly
 

mohamed.elsabagh said:
Now the problem is when the thermocouple moves on a surface like pcb or something for sometime the lcd shows some strange characters on the lcd or it doesn't show anything at all, but when the microcontroller is reset every thing goes to normal. what might be the cause of the problem? the software driver may have a problem??or what else?
Click to expand...
There is a possibility that a problem exists with the lcd code. When the temperature is changing there might be data sent to the lcd, out of the ascii character range. If so, then the characters are not printable. Is the lcd code tested, have you used this code with success in other projects as well?
You can understand if this is the actual problem, by doing the following test. Before you send a character to the lcd check its value. If the value is smaller than 0x20 or greater than 0x7E, then send another character instead, like let's say 'F' (fault). When this thing happens again if you see an LCD with 'F' characters, then the problem is with the lcd code. If on the other hand the same behaviour is observed, you should look into memory overflow issues, or bad command send to the lcd at some point.

Regards,
Alexandros
 
alexxx said:
There is a possibility that a problem exists with the lcd code. When the temperature is changing there might be data sent to the lcd, out of the ascii character range. If so, then the characters are not printable. Is the lcd code tested, have you used this code with success in other projects as well?
You can understand if this is the actual problem, by doing the following test. Before you send a character to the lcd check its value. If the value is smaller than 0x20 or greater than 0x7E, then send another character instead, like let's say 'F' (fault). When this thing happens again if you see an LCD with 'F' characters, then the problem is with the lcd code. If on the other hand the same behaviour is observed, you should look into memory overflow issues, or bad command send to the lcd at some point.

Regards,
Alexandros
Click to expand...

Actually i think the code itself is working fine because i have been using it with the lcd for such long time, but maybe you are right. maybe the code needs more investigation, even though it's a good idea to use such condition for safety on the lcd if it won't solve the problem it wouldn't harm. i like this idea :), although i think the problem is more complicated because the max6675 send digital data to the microcontroller in range of 1023 and i use a function convert the number into array of digits or char and then send it to write_char function which accepts char range also, and there are some messages in character should appear on the lcd like : Temper. = xxx C this messages and character all disappear from the screen suddenly. anyhow i will use you idea and feed you back with the results thanks so much man.
 

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