A/D converter fails?

[egberttheone]

I'm building a system to monitor a few powerlines it works well but some times the conversion results into a 0; i took the data sheet of the pic i use (16f88) read the whole chapter about it over and over and i finished up changing my code(snippets; of course the enable bit and so are set) from this:

'GO/DONE: A/D Conversion Status bit
'If ADON = 1:
'1 = A/D conversion in progress (setting this bit starts the A/D conversion)
'0 = A/D conversion not in progress (this bit is automatically cleared by hardware when the A/D
'conversion is complete)
symbol AD_Progress = ADCON0.2


ADCON0.5 = 0
ADCON0.4 = 0
ADCON0.3 = 0
AD_Progress = 1
while AD_Progress = 1: wend
Sound_Level.lowbyte = ADRESL
Sound_Level.highbyte = ADRESH

to this:

'GO/DONE: A/D Conversion Status bit
'If ADON = 1:
'1 = A/D conversion in progress (setting this bit starts the A/D conversion)
'0 = A/D conversion not in progress (this bit is automatically cleared by hardware when the A/D
'conversion is complete)
symbol AD_Progress = ADCON0.2

ADCON0.5 = 0
ADCON0.4 = 0
ADCON0.3 = 0
pause 50
AD_Progress = 1
while AD_Progress = 1: wend
Sound_Level.lowbyte = ADRESL
Sound_Level.highbyte = ADRESH

as I understood of the manual: if I change the input port from the a/d converter I need to wait a minimum of time before recalling a new a/d conversion. So far so good but what happens is it stucks @ "while AD_Progress = 1: wend" because it simply does not clear any more the code above without the pause 50 does work! so if I remove that line "pause 50" the code runs but some times I get a 0 in the result of the a/d conversion :S I don;t get it do you?

[Bruce]

ADCON0.0 = 1 ' <-- Turn ON A/D module

[egberttheone]

ADCON0.0 = 1 ' <-- Turn ON A/D module

please read before replying; i told that all these bits are set AND i sad that it works without the pause command or do you want to say that beacause i added the command line "pause 50" that the a/d conversion module shuts off?

[Bruce]

Sorry. It's hard to "guess" how you're configuring things if you don't show it in your code.

I'm sure this isn't what the rest of your own application is doing, but it works fine with the
pause 50 in there;

    @ DEVICE HS_OSC, WDT_ON, LVP_OFF, PROTECT_OFF
    DEFINE OSC 20
    
    SYMBOL AD_Progress = ADCON0.2
    SYMBOL ADON = ADCON0.0
    SYMBOL LED = PORTB.0
  
    Sound_Level VAR WORD
    
    TRISA.0 = 1     ' A/D input
    PORTB.0 = 1     ' LED on at boot
    TRISB.0 = 0     ' LED output
      
    ADCON0 = 128 ' A/D clock Fosc/32, RA0/AN0, A/D disabled
    ANSEL = 1       ' RA0 analog
    ADCON1.7 = 1  ' right justify for 10-bit

Main:
    ADON = 1        ' turn on A/D module
    PAUSE 50        ' wait
    AD_Progress = 1 ' start conversion
    
    WHILE AD_Progress = 1 : WEND
    Sound_Level.lowbyte = ADRESL
    Sound_Level.highbyte = ADRESH
    LED = LED ^ 1    ' toggle LED for visual
    GOTO Main
    
    END

I left the WDT enabled just to be sure PBP was handling it during the pause periods.

[egberttheone]

this code works but if you change the input port of the a/d convertor and then add a pause in the line between changing and a/d conversions start then it stucks.

example:

'retrieve sound level
ADCON0.5 = 0
ADCON0.4 = 0
ADCON0.3 = 0
pause 50
AD_Progress = 1
while AD_Progress = 1: wend
Sound_Level.lowbyte = ADRESL
Sound_Level.highbyte = ADRESH

'retrieve negative level
ADCON0.5 = 0
ADCON0.4 = 0
ADCON0.3 = 1
pause 50
AD_Progress = 1
while AD_Progress = 1: wend
Negative_Voltage.lowbyte = ADRESL
Negative_Voltage.highbyte = ADRESH

'retrieve positieve level
ADCON0.5 = 0
ADCON0.4 = 1
ADCON0.3 = 0
pause 50
AD_Progress = 1
while AD_Progress = 1: wend
Positive_Voltage.lowbyte = ADRESL
Positive_Voltage.highbyte = ADRESH

[Bruce]

That's odd. It works for me without getting stuck.

I modified your version to include 3 LED's in the last section of each channel read routine,
and all 3 LED's blink right along.

It doesn't appear to be getting getting stuck at any point.

    @ DEVICE HS_OSC, WDT_ON, LVP_OFF, PROTECT_OFF
    DEFINE OSC 20
    
    SYMBOL AD_Progress = ADCON0.2
    SYMBOL ADON = ADCON0.0
    SYMBOL LED1 = PORTB.0
    SYMBOL LED2 = PORTB.1
    SYMBOL LED3 = PORTB.2
  
    Sound_Level VAR WORD
    Negative_Voltage VAR WORD
    Positive_Voltage VAR WORD
    
    TRISA.0 = 1         ' A/D input
    PORTB = %00000111   ' LED's on at boot
    TRISB = 0           ' LED outputs
      
    ADCON0 = 128    ' A/D clock Fosc/32, RA0/AN0, A/D disabled
    ANSEL = 1       ' RA0 analog
    ADCON1.7 = 1    ' right justify for 10-bit

Main:
    ADON = 1        ' turn on A/D module
    PAUSE 50        ' wait
    AD_Progress = 1 ' start conversion 
    WHILE AD_Progress = 1: WEND
    Sound_Level.lowbyte = ADRESL
    Sound_Level.highbyte = ADRESH
    LED1 = LED1 ^ 1    ' toggle LED for visual
    
    'retrieve negative level
    ADCON0.5 = 0
    ADCON0.4 = 0
    ADCON0.3 = 1
    PAUSE 50
    AD_Progress = 1
    WHILE AD_Progress = 1: WEND
    Negative_Voltage.lowbyte = ADRESL
    Negative_Voltage.highbyte = ADRESH
    LED2 = LED2 ^ 1    ' toggle LED for visual
    
    'retrieve positieve level
    ADCON0.5 = 0
    ADCON0.4 = 1
    ADCON0.3 = 0
    PAUSE 50
    AD_Progress = 1
    WHILE AD_Progress = 1: WEND
    Positive_Voltage.lowbyte = ADRESL
    Positive_Voltage.highbyte = ADRESH
    LED3 = LED3 ^ 1    ' toggle LED for visual
    GOTO Main
    
    END

Are you reading 0-5 VDC voltage levels?