adc conversion

[elie]

Hi, i would like to ask about a certain problem occuring with me during the adc conversion..instead of converting 4v for example to the right binary number at the output..i'm always getting an answer at the output less than arounf 0.5v from the real voltage at the input..what's the solution?

 

[Wp100]

Hi,

No one can make make a qualified judgement without seeing both your source code and full circuit diagram, you do not even mention the micro or programming code you are using.

Please post them so we can look into your problem more.

 

[Umma]

Please Send ADC IC No and source code taht you are using

 

[ericgibbs]

I am puzzled why the OP thinks this problem, which is specific to his project/program is a topic for a POLL.???

IMHO it belongs in the micro-controllers Forum

 

[elie]

the pic number is 16F877...this is part of the source code:

A2D_CHANNEL_0
MOVLW B'01000001'
MOVWF ADCON0
CALL A2D_DELAY
BSF ADCON0,GO
BTFSC ADCON0,GO
GOTO $-1
MOVF ADRESH,W
RETURN

 

[elie]

hi all, in my project i'm using different types of sensors on a multiplexer and they're all going through adc conversion. if the output of one sensor is 4v for example, the microcontroller sends 3.5v after converting it to digital..there's always this gap in the voltage...should i place any voltage buffer after each sensor to prevent this drop down or what?

 

[Nigel Goodwin]

the pic number is 16F877...this is part of the source code:

A2D_CHANNEL_0
MOVLW B'01000001'
MOVWF ADCON0
CALL A2D_DELAY
BSF ADCON0,GO
BTFSC ADCON0,GO
GOTO $-1
MOVF ADRESH,W
RETURN

You're only showing a tiny part of the code, and if you're only reading ADRESH then (depending on the setup) you're only reading the top two bits.

Check my analogue inputs tutorial.

 

[elie]

yes i'm only interested in the highest 8 bits and i want to neglect the least 2 signigicant bits since the encoder connected to the microcontroller can only read 8 data bits and not 10

 

[3v0]

hi all, in my project i'm using different types of sensors on a multiplexer and they're all going through adc conversion. if the output of one sensor is 4v for example, the microcontroller sends 3.5v after converting it to digital..there's always this gap in the voltage...should i place any voltage buffer after each sensor to prevent this drop down or what?

What multiplexer are you using ?

 

[Nigel Goodwin]

yes i'm only interested in the highest 8 bits and i want to neglect the least 2 signigicant bits since the encoder connected to the microcontroller can only read 8 data bits and not 10

But you've shown no code to suggest that's what you're doing - it's useless posting only what you have.

 

[superflux]

But you've shown no code to suggest that's what you're doing - it's useless posting only what you have.

It would certainly be nice to know if your ADC result is left or right justified.