In SX Microcontrollers, SX/B Compiler and SX-Key Tool, PismoSpike wrote:

Hey everyone!

I am trying to use the Analogin command to read up to 255V. I have calculated that I need a 1 MOhm resistor to achieve this. Unfortunately it would seem that this is too high of a value to charge/discharge the capacitor when I measure voltages from 0-15V (thats all I have available). 
 

                    10K               1M
'RA.1 Pin ----\/\/\/-----+---\/\/\/----- Voltage to measure
'                                |
'RA.0 Pin --------------+
'                                | 0.01uF
'                                +--|(-- GND

In this configuration the reading is ~127,~128 when I am measuring anything from 0-10V and it slowly rises as I go above 10V.
I can't figure out how to get calibrate this ADC. I would greatly appreciate any help. 

Oh, and is there a way to write a VP ADC for greater than 8 bit precision, say 12 bit?   

Thanks


My code so far:
Uses a 3 digit 7 segment array as output.

 
'-----------------------------------------
'DIRECTIVES
'-----------------------------------------

DEVICE          SX28, OSC4MHZ, TURBO, STACKX, OPTIONX
FREQ            4_000_000

'-----------------------------------------
'I/O Pins 
'-----------------------------------------

Seg7            PIN RC    output                  '7 segment ouptut
Digit1           PIN RB.7  output                  'pin for least significant digit
Digit2           PIN RB.6  output  
Digit3           PIN RB.5  output                  'Most significant digit 
InPin            PIN RA.0  INPUT CMOS          'Analogin command
OutPin          PIN RA.1  OUTPUT                'Analogin command

'-----------------------------------------
'Constants
'-----------------------------------------

turnoff  CON  1                                  'High because digits are common cathode. If common anode flip values. 
turnon   CON 0                                   'If low then current will flow from segment to common.

'-----------------------------------------
'Variables
'-----------------------------------------

DispTime          VAR BYTE                    'speed of counter.
SensorReading  VAR BYTE
SenOnesVal      VAR BYTE
SenTensVal      VAR BYTE
SenHundVal      VAR BYTE

'-----------------------------------------
'MAIN PROGRAM
'-----------------------------------------

PROGRAM Start

Start:

 DO

     ANALOGIN InPin, OutPin, SensorReading, 4    


     SenHundVal = SensorReading/100   
     SenTensVal = __REMAINDER/10   
     SenOnesVal = __REMAINDER



     DispTime = 0 
   DO 

     Digit1  = turnon   
     READ Dig_Map + SenOnesVal, Seg7    
     PAUSE 1    
     Digit1  = turnoff   
     Digit2  = turnon
     READ Dig_Map + SenTensVal, Seg7
     PAUSE 1
     Digit2  = turnoff
     Digit3  = turnon
     READ Dig_Map + SenHundVal, Seg7
     PAUSE 1
     Digit3  = turnoff
    

     INC DispTime    

   LOOP UNTIL DispTime = 150   

 LOOP 
 
END 
 


Dig_Map:
' bafg.cde
DATA %11100111 ' 0
DATA %10000100 ' 1
DATA %11010011 ' 2
DATA %11010110 ' 3
DATA %10110100 ' 4
DATA %01110110 ' 5
DATA %01110111 ' 6
DATA %11000100 ' 7
DATA %11110111 ' 8
DATA %11110110 ' 9

---------- End of Message ----------


You can view the post on-line at:
http://forums.parallax.com/forums/default.aspx?f=7&p=1&m=330585

Need assistance? Send an email to the Forum Administrator at forumadmin@parallax.com

The Parallax Forums are powered by dotNetBB Forums, copyright 2002-2009 (http://www.dotNetBB.com)