query on the ADC0

[nagendramurthy]

Hello everyone, 

I'm working on the LPC1837 micro controller. i have a query regrading the ADC conversion of the ADC0 channel 0. 

ADC0 channel 0 has be connected to the port 4 and pin 3 of the micro controller. as per the data sheet , i have matched it. 

Question: I'm feeding the fixed voltage of 12.5 v to the  ADC 0 channel 0. but when i'm output value is varies from 0 to max and  again decrease from Max to 0. 

i'm facing the issue only in the channel. 

where as the output for the other channel are obtain are correct. 

[kerryzhou]

Hi nagendra murthy,

   Mike is correct.

   You can't input the 12.5V to the ADC0.0 directly.

From the datasheet, you can get that the ADC input voltage can't exceed 3.3V.

I am afraid your pin is damaged.

Do you have any other board? Please try your code on another board, and make sure the adc input voltage is below 3.3V.

If your result is still not OK, please check EDAIO0, make sure you configure ADC0_0 as the analog function on pin P4_3:

Wish it helps you!

Have a great day,
Kerry

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[mikesimmonds]

Hi There.

I am pretty sure that the maximum voltage that may be applied to an ADC pin must be less than or equal to VRef. Which is probably 3.3 Volts. You will need voltage dividers on the ADC inputs. You may have already damaged the device by over voltage.

Cheers, Mike.