How to solve the problem of unstable ADC values?

[firmware]

ADC

Hello everybody...

I'm new member for this weboard. I have some problem about the ADC of microcontroller, I make the temperature measurement project by using the thermister (NTC), it is OK. But some time the ADC value is not so stable, I try to improve hardware by add the filter. But not so good. Somebody know the software technic pls help me. I use 8 bit ADC


Best regards,

 

[sci-3d]

Re: ADC

Could give more details about what your MCU or your ADC.

 

[firmware]

Re: ADC

Thank you for your reply.
I using NEC MCU uPD78F0523, this MCU have 10 bit ADC, but I use only 8 bit, I need to measure temperature from -10 to 70 degree by 0.5 step.


Best regards,

Added after 7 minutes:

My concept to get the ADC value from MCU by using voltage divider circuit, and point to the temperature table that made from thermister formula.

 

[nikhil_damle]

Re: ADC

our requirnmrnt is 8 bit data out of the 10 bit adc
take a=adc value

and a with 0X0ff

u will probably get what u want

 

[firmware]

Re: ADC

This MCU provide the register for ADC 8 bit already, I can read the ADC 8 bit from this register, I try to find some technic for get the real data from ADC, because it vary one or two at last of 8 digit of ADC.

 

[Jepeto]

Re: ADC

This problem can be caused when the internal sample and hold capacitor not charged to the input voltage value because off high resistance value of the sensor output or selecting short converting time
You can do software filter by averaging 4 or 8 measures results and or reject sudden measuring changes

 

[maggots]

ADC

i dont have experiment about that MCU but i think U can make maybe 10 times samples and make average of that databefore U use the data.....

 

[amrstaha]

Re: ADC

I had a similar problem before and it was mainly due to noise. Try the magic if using a shielded cable for your sensor. Also try to isolate the analog ground from the digital ground (they shouldn't meet except at the power supply terminal). The filter would help you remove power frequency niose (50 or 60 Hz). And finally you can use a simple software digital filter (a simple one is to read say 5 readings, sum them up and then divide the result by 5)

Hope this helps you.