Strange ADC behaviour

[mister_e]

NO NO NO DON'T DO IT

Vref have to be lower than Vdd. Let's see you have a sensor who produce you a max of 1 volt. Then you select a Vref of ~1 Volt, then your ADC give you the full 10 bit conversion scale between 0-Vref. This is the use of it.

But yeah.. check out for the minimum Vref requirement...

[Acetronics2]

NO NO NO DON'T DO IT

Vref have to be lower than Vdd. Let's see you have a sensor who produce you a max of 1 volt. Then you select a Vref of ~1 Volt, then your ADC give you the full 10 bit conversion scale between 0-Vref. This is the use of it.

Hi, Steve

a LM 385 or 385-1.2 will make a nice ( and cheap ! ...) 1.235 v reference here ...

BUT, do not forget the higher the signal ... the smaller the noise ! ( and last digit flickering ! ) ...
so, here, the sensor choice is " not so good" ... If I understood (?) , our friend wants to read ambiant temp ... 150-250 mv levels !


( note an OPA will amplify noise + signal ... "not so good" solution too ...)

Alain

[ruijc]

Hello Alain,

the purpose of this circuit is first to learn
Then it will be for reading temperatures between 20 and 130ºC.

The forum mentioned the LM335 as the best choice but this one does not reach above 100ºC.

I had the LM35 and the LM135 ( which does accept temps higher than 100ºC ) on my list.

The problem is than my local store does not have the LM135 so i'm kinda stuck with this one !

I will retry to write the code with your tip :

" temp = val*125
temp = temp.highbyte "


.