[SOLVED] LPC23xx ADC programming

[bikashh]

Dear friend thanks a lot for your support.

Now i set my Trimpot output to 2V and getting variations in readings.
Terminal output:

ADC BINARY DATA-> 1001100001
ADC BINARY DATA-> 1001101000
ADC BINARY DATA-> 1001100000
ADC BINARY DATA-> 1001101001
ADC BINARY DATA-> 1001100001
ADC BINARY DATA-> 1001100001
ADC BINARY DATA-> 1001100001
ADC BINARY DATA-> 1001100001
ADC BINARY DATA-> 1001100001
ADC BINARY DATA-> 1001100001
ADC BINARY DATA-> 1001101001
ADC BINARY DATA-> 1001100010
ADC BINARY DATA-> 1001100001
ADC BINARY DATA-> 1001100001
ADC BINARY DATA-> 1001100010
ADC BINARY DATA-> 1001100001

May be this variation is because of Vref. can i use a 3V zener to fix the same?

Thanks

i've checked my Vref for 3.3V using a multimeter but its quite stable.

 

[alexan_e]

There will be some variation because of noise of maybe power supply or digital interference, in your case it seems to be up to 20mv difference

May be this variation is because of Vref. can i use a 3V zener to fix the same?

Where do you want to use the diode?

Alex

 

[bikashh]

To fix the Vref to 3v i want to use zener diode

 

[alexan_e]

You can use a resistor with a zener and a capacitor to feed the Analog input with lower voltage but the zener solution doesn't have a very accurate voltage output and varies with temperature.
A dedicated reference voltage ic would be better or a Programmable Shunt Regulator like TL431
Do you need that much accuracy?

Alex

 

[bikashh]

My terminal output:

binary is->1111111110
decimal data->1022
MV data->3.2908mv


binary is->1111111100
decimal data->1020
MV data->3.2844mv


binary is->1111111110
decimal data->1022
MV data->3.2908mv

binary is->1100100100
decimal data->804
MV data->2.5888mv


binary is->1100011110
decimal data->798
MV data->2.5695mv


binary is->1100100110
decimal data->806
MV data->2.5953mv


binary is->1100101000
decimal data->808
MV data->2.6017mv

binary is->1001100100
decimal data->612
MV data->1.9706mv


binary is->1001011010
decimal data->602
MV data->1.9384mv


binary is->1001011010
decimal data->602
MV data->1.9384mv


binary is->1001011010
decimal data->602
MV data->1.9384mv


binary is->1001011001
decimal data->601
MV data->1.9352mv

I haven't tested in actual device.lets see how the actual device respond.
My actual device is a level sensor with 5mm resolution.whose resistance changes after every 5mm with 5ohm.
I am planning to sense the change in temperature using a voltage divider.In which R1 would be fixed while R2 would be sensor.the change in output would be fed to ADC of the controller.
the range of my level sensor is6 to 67ohm.