A/D converter fails?

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- 7th February 2006, 20:34
egberttheone

A/D converter fails?

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:

Code:

'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:

Code:

'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?
- 7th February 2006, 23:32
Bruce

ADCON0.0 = 1 ' <-- Turn ON A/D module
- 8th February 2006, 19:22
egberttheone

Quote:

Originally Posted by Bruce

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?
- 8th February 2006, 21:05
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;

Code:

@ 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.
- 8th February 2006, 21:09
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:

Code:

'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
- 8th February 2006, 21:42
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.

Code:

@ 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?
- 9th February 2006, 18:13
egberttheone

yes, i'm reading voltage's between 0-5VDC. i found out that it doesn't mather where i place the pause command(in the interrupt routine); it instant freez the pic forever. The AD routine is placed in a interrupt routine is it not possible to place a pause periode into a interrupt handel?

note: timer0, timer1 and serial interrupt are activated.
- 13th February 2006, 17:08
egberttheone

any one ? :(
- 13th February 2006, 17:19
Bruce

Are you using BASIC or assembler interrupts?

Can you post the code you're having problems with?
- 13th February 2006, 17:53
egberttheone

i do not want to post the code; but i can email it to you. i'm using the basic interrupt routine (on interrupt goto handel)
- 13th February 2006, 18:06
Bruce

Are you clearing "all" interrupt flags before exiting your interrupt handler?
- 13th February 2006, 18:09
egberttheone

Yes, but can i use a pause command in the interupt?

Code:

Disable ' interrupt handler Handle: if RCIF = 1 then ' serial intterupt RCIF = 0 ' clearing interrupt flags IF OERR THEN ' Clear over-runs if OERR set CREN = 0 ' Disable USART receive CREN = 1 ' Re-enable USART receive ENDIF 'Serial commands. endif IF TMR0IF = 1 THEN 'RECEIVE all A/D value's TMR0IF = 0 gosub CoversionsAD gosub saftycontrol 'check al received value's ENDIF if TMR1IF = 1 then TMR1IF = 0 gosub PacketSend endif TimeOut: resume enable
- 13th February 2006, 18:28
Bruce

You can use all the pause statements you want inside a BASIC interrupt, however, I don't recommend you place gosubs in your interrupt handler.

This exits the interrupt handler, and if it lands in a sub routine where you are not disabling PBP's auto-insertion of interrupt checking stubs, then it's going to go totally nuts on you.

Place all of your routines inside the interrupt handler, or set/clear some type of flags to indicate the interrupt source, then return, then act on the other sub routines as needed.

Also note that RCIF can NOT be cleared with RCIF = 0. The only way to clear RCIF is to read the fifo USART buffer until it's empty. Trying to clear this flag like you are, you're leaving it set, and never clearing the USART interrupt flag bit.
- 13th February 2006, 18:45
egberttheone

ah! the gosubs seems to be the problem :) ! but now I have the problem that the a/d conversion some times fluctuates(value's are not the same every querying + 1000 some times). Where can I begin to debug? Thx !
- 13th February 2006, 18:57
Bruce

A/D readings will pretty much always fluctuate. A small RC filter on each A/D input may help. If not, you might consider putting the PIC to sleep prior to A/D readings to reduce in-circuit noise from the oscillator & internal switching.

If you think "code" may be causing the fluctuations, then simply strip down the program to nothing but reading & displaying A/D values. If it works smoothly, then take a hard look at the rest of your code.