A2D question

[dbodenheimer]

I am working on what I thought was a simple PIC project and I need some help.

What I need to do is an Analog to digital conversion on an 0-5v signal on RA0 and then put the result in a 4 byte array so that I can send the data to a serial port.

I have used the example for USART and have that working, so I can send data to the serial port ok. I just need to do the A2D conversion and convert to characters I can transmit
IM using an PIC 16F876.

Thanks in Advance!

Dave

[kevlar129bp]

Hey Dave,

I don't know if I can help, but my project is basically doing that now... I think the more experienced gurus on the forum are going to request your code so far. Post that, and you'll have tons of help.

Chris

[dbodenheimer]

Here is my code, feel free to offer suggestions or modifications.

' Read and write hardware USART

B1      var     byte
Done    var     byte
TxBuf   var     byte[3]
STX     var     byte
ETX     var     byte
Period  var     byte
i       var     byte
tmpval var     byte
' Initialize USART
        TRISC = %10111111       ' Set TX (PortC.6) to out, rest in
        SPBRG = 25              ' Set baud rate to 2400
        RCSTA = %10010000       ' Enable serial port and continuous receive
        TXSTA = %00100000       ' Enable transmit and asynchronous mode

' Define ADCIN parameters
Define    ADC_BITS    10         ' Set number of bits in result
Define    ADC_CLOCK    3         ' Set clock source (3=rc)
Define    ADC_SAMPLEUS    50     ' Set sampling time in uS

adval    var    word        ' Create adval to store result


    TRISA = %11111111    ' Set PORTA to all input
    ADCON1 = %10000010    ' Set PORTA analog and right justify result
    Pause 500        ' Wait .5 second


' Echo received characters in infinite loop
STX = 2
ETX = 3
Period = 46
TxBuf[1] = 51
TxBuf[2] = 54
TxBuf[3] = 56
mainloop: 
        ADCIN 0, adval    ' Read channel 0 to adval
'basicaly here i want to convert advar into 3 ascii numbers
'representing advar
'So a result like 936 would put 
'57 in txbuf[1] 
'51 in txbuf[2]
'54 in txbuf[3]
'Then call the serial output routine which adds a stx char, 2 digits
'a period then the last digit followed by an ETX char
        Gosub StringOut         ' Send character to serial output
        pause 500               ' Wait half second
        Goto mainloop           ' Do it forever


' Subroutine to get a character from USART receiver
charin: B1 = 0                  ' Preset to no character received

        If PIR1.5 = 1 Then      ' If receive flag then...
                B1 = RCREG      ' ...get received character to B1
        Endif

ciret:  Return                  ' Go back to caller


' Subroutine to send a character to USART transmitter
charout: If PIR1.4 = 0 Then charout     ' Wait for transmit register empty
               
        TXREG = B1              ' Send character to transmit register
       done = 1
        Return                  ' Go back to caller
' Subroutine to send a character string to USART transmitter
'First Send STX (02)  then 2 digits, then period (46), then 1 digit, then ETX (03)
StringOut: If PIR1.4 = 0 Then StringOut     ' Wait for transmit register empty
       done = 1
               
       TXREG = STX              ' Send character to transmit register
       while PIR1.4 = 0
       wend
       for i = 1 to 2
           TXREG = TxBuf[i]              ' Send character to transmit register
           while PIR1.4 = 0
           wend
       next i
       TXREG = Period              ' Send character to transmit register
       while PIR1.4 = 0
       wend
       TXREG = TxBuf[3]              ' Send character to transmit register
       while PIR1.4 = 0
       wend
       TXREG = ETX              ' Send character to transmit register
       while PIR1.4 = 0
       wend
    Return                  ' Go back to caller

[mackrackit]

Put your code in code tags and post it. Not going to risk or take the time to download and open a ZIP when a ZIP is not needed.

put the result in a 4 byte array

This chip only has a 10 bit resolution so you need to explain what you are after. The ADC result can be sent serially with out an array of ant type...

Here is a sample to read the ADC at an 8 bit resolution. Maybe it will get you started.

ADCON1 = %00001110
OUT_TEMP VAR BYTE

MAIN_LOOP:
  GOSUB GET_AD
  GOTO MAIN_LOOP

GET_AD:
  ADCON0=00000001
  GOSUB READ_AD
  OUT_TEMP = ADRESH
  RETURN
  
  READ_AD:
  PAUSE 50
  ADCON0.2=1
  WHILE ADCON0.2=1:WEND
  RETURN

[mackrackit]

    txbuf[1] = advar / 1000  
    txbuf[2] = (advar - txbuf[1] * 1000) /100  
    txbuf[3] = (advar-((txbuf[1] * 1000) + (txbuf[2] * 100)))/10  
    txbuf[4] = advar - ((txbuf[1] * 1000) + (txbuf[2] * 100)+ txbuf[3] * 10)

[aratti]

TxBuf var byte[3]

'basicaly here i want to convert advar into 3 ascii numbers
'representing advar
'So a result like 936 would put
'57 in txbuf[1]
'51 in txbuf[2]
'54 in txbuf[3]
'Then call the serial output routine which adds a stx char, 2 digits
'a period then the last digit followed by an ETX char

Dave, with referece to your code please note that when you declare an array, the number you state is the real number of elements of your array. you stated 3 elements, so you will have the following bytes available:

txbuf[0]
txbuf[1]
txbuf[2]

Now since you are decoding a 10bits adc then the maximum reading you can obtain in adval is 1023, which are four digits so you will need a 4 bytes array for your data transfer.
Hence, you have to declare:

txbuf var byte [4]

and you will have the following bytes available:

txbuf[0]
txbuf[1]
txbuf[2]
txbuf[3]

Please read page 33 of PBP manual, you will find the DIG instruction that could help you in moving the single digits into your array. Here a snippet as an example:

A  var byte   ' used for the FOR/NEXT loop

For A=0 to 3
txbuf[A]= adval DIG A
next A

'assuming adval contains the value 1023 then your array will end up as follows:

'txbuf[0]="3"
'txbuf[1]="2"
'txbuf[2]="0"
'txbuf[3]="1"

In case you want them the other way then

For A=0 to 3
txbuf[A]= adval DIG (3-A)
next A


'will yield:

'txbuf[0]="1"
'txbuf[1]="0"
'txbuf[2]="2"
'txbuf[3]="3"

Al.

[dbodenheimer]

Thanks Everyone for the input! I'm now able to read values from my sensor. I now have 2 additional questions.

1. Is there a better way to send serial; data than the way I'm doing it? Anyone have a routine that they think works better?

2. It seems like my returned values vary quite a bit. I don't have access to a scope, but it seems that the sensor is returning pretty constant voltage. it returns 0 - 10 v I am using a voltage divider made up of 2 2.2 K resistors to shift the sensor output to 0 - 5 volts. Any hints on making the system more stable? Slow down the conversion time? My requirements are pretty easy, i need to read the sensor no more than twice a second.

Thanks again for everyone's help!

Dave