MCP3002 not displaying voltage jumps

Dave A

Can anyone help me. I am using the sample program for the MCP3002 to display voltage. It only shows either "0" or 79.99 on both channels.
The following is the code I am using.


#include "simpletools.h" // Include simpletools
#include "adcDCpropab.h" // Include adcDCpropab

int main() // Main function
{
adc_init(8, 9, 10, 11); // CS=Pin1, SCL=Pin7, DO=Pin6, DI=Pin5

float v0, v1; // Voltage variables

while(1) // Loop repeats indefinitely
{
v0 = adc_volts(0); // Check A/D 0
v1 = adc_volts(1); // Check A/D 1

putChar(HOME); // Cursor -> top-left "home"
print("A/D0 = %f V%c\n", v0, CLREOL); // Display volts
print("A/D1 = %f V%c\n", v1, CLREOL); // Display volts

pause(100); // Wait 1/10 s
}
}


Anyone's assistance will be appreciated.
Dave

yisiguro

Is a comment below a help here ?

http://forums.parallax.com/discussion/comment/1221392/#Comment_1221392

The adcDCpropab.h is designed to communicate with the ADC on the Propeller Activity board which is a "ADC124SO21"

iseries

I wrote a library function for MCP3202 chip but it is easy enough to just read the values from the chip.

Here is the code to read MCP3202 chip:

// millivolts times 1000
int mcp3202_read(int R)
{
  unsigned int i;
  
  if (R == 0)
    i = 0xd; //1101
  else
    i = 0xf; //1111

  low(mcpCS);
  shift_out(mcpDIN, mcpCLK, MSBFIRST, 4, i);
  i = shift_in(mcpDOUT, mcpCLK,  MSBPOST, 12);
  high(mcpCS);
  return i;
}
  
int mcp3202_volts(int R)
{
  int i;
  
  i = mcp3202_read(R);
  i = i * 1000;
  i = i / 1226;
  return i;
}

Since this chip has two ADC lines the variable R is really the channel you want to read.

Also the MCP3002 is only a 10 bit resolution chip so you need to change the 12 above to 10.

Mike

Dave A

Mike, I had to add code, your code was incomplete. But I am not getting anything on my display

// millivolts times 1000
#include "simpletools.h" // Include simpletools

#include <propeller.h>

#include "adcDCpropab.h" // Include adcDCpropab
const int ON = 254;
const int CLR = 1;
int main()
{ // Main function
int mcp3202_read(int R)
{

int mcpCS = input(8);
int mcpDIN = input(11);
int mcpCLK = input(7);
int mcpDOUT = output(6);
unsigned int i;

if (R == 0)
i = 0xd; //1101
else
i = 0xf; //1111

low(mcpCS);
shift_out(mcpDIN, mcpCLK, MSBFIRST, 4, i);
i = shift_in(mcpDOUT, mcpCLK, MSBPOST, 10);
high(mcpCS);
return i;

}
int mcp3202_volts(int R)
{
int i;

i = mcp3202_read(R);
i = i * 1000;
i = i / 1226;
pause(100);
serial *lcd = serial_open(12, 12, 0, 9600); //Pin12 out,pin12 in,data bits 0,baud rate 9600
writeChar(lcd, ON);
writeChar(lcd, CLR);
dprint(lcd,"Volts %d", i); //display volts
pause(100);
return i;
}
}

Your assistance will be appreciated.
Dave

Publison

As per the second post, do you really want to include "adcDCpropab.h"? That's a completely different ADC. I many not even affect your program.

Also when posting, please use coding brackets, (the big C in the editor). This will show code as it is supposed to be viewed. When the "Code/code) shows up copy and paste your code between the brackets.

iseries

Here some code to display the voltage on the LCD display.

I used two resistors 10K each with 5 volts. This would result in a voltage of 2.5 volts

Attached is a picture of the setup with an MCP3204 chip connect between the two 10k resistors with a voltage reading of 2.5

#include "simpletools.h"

// pre define function
int readMCP3204(char);
int readMCP3002(char);

const char ON = 22;
const char CLR = 12;
const char H = 128;
const char L2 = 192;

#define BLTON 17

#define CLK  2
#define DOUT 3
#define DIN  4
#define CS   5

// high bit is start bit
#define CHANNEL 0x18
#define TWOCHANNEL 0x06


int i;
serial *lcd;
float v;

int main()
{
  lcd = serial_open(8, 8, 0, 19200); //Pin12 out,pin12 in,data bits 0,baud rate 9600
  
  writeChar(lcd, ON);
  writeChar(lcd, BLTON);
  
  input(DOUT);
  
  low(CS);
  high(CS);
  

  while (1)
  {
    i = readMCP3204(1);
    print("Value: %d\n", i);
    v = i;
    v = v / 4096 * 5; // digital output code =(4096 * Vin) / Vdd
    dprint(lcd, "%cVolts: %f", CLR, v);
    pause(1000);
  }      
}

// c = channel pin
// rotate 1 to set conversion start
int readMCP3204(char c)
{
  short v;
  
  low(CS);
  v = (CHANNEL + c) << 1;
  shift_out(DIN, CLK, MSBFIRST, 6, v);
  v = shift_in(DOUT, CLK, MSBPOST, 12);
  high(CS);
  return v;
}

int readMCP3002(char c)
{
  short v;
  
  low(CS);
  v = (TWOCHANNEL + c) << 1;
  v = v | 0x01; // MSBF bit value
  shift_out(DIN, CLK, MSBFIRST, 4, v);
  v = shift_in(DOUT, CLK, MSBPOST, 10);
  high(CS);
  return v;
}

This code will not work for MCP3002 as it only has 2 inputs and require a MSBF bit. The readMCP3002 function should work instead. Also the reading changes as it is only 10 bits so the new formula is: reading = (1024 X Vin) / Vdd

Solving for Vin would be:

v = v / 1024 * 5


Mike

Dave A

Mike, it is kind of working, but what is happening, like on my display, it will read up to 400 then it starts over again and does this for 3 times. It does this with the terminal view except it is a 4 digit number. I made a few changes to work with my setup.

#include "simpletools.h"

// pre define function
int readMCP3204(char);
int readMCP3002(char);

const char ON = 254;
const char CLR = 1;
const char H = 128;
const char L2 = 192;

#define BLTON 17

#define CLK 9
#define DOUT 10
#define DIN 11
#define CS 8

// high bit is start bit
#define CHANNEL 0x18
#define TWOCHANNEL 0x06

int n;
int i;
serial *lcd;
float v;

int main()
{

input(DOUT);

while (1)
{
i = readMCP3204(1);
print("Value: %d\n", i);

lcd = serial_open(12, 12, 0, 9600); //Pin12 out,pin12 in,data bits 0,baud rate 9600
writeChar(lcd, ON);
writeChar(lcd, CLR);
i = readMCP3204(1);
n = i;
n = n/10;
dprint(lcd, "Volts: %d",n );
pause(1000);
}
}

//c = channel pin
//rotate 1 to set conversion start
int readMCP3204(char c)
{
short v;

low(CS);
v = (CHANNEL + c) << 1;
shift_out(DIN, CLK, MSBFIRST, 6, v);
v = shift_in(DOUT, CLK, MSBPOST, 12);
high(CS);
return v;
}

int readMCP3002(char c)
{
short v;

low(CS);
v = (TWOCHANNEL + c) << 1;
v = v | 0x01; // MSBF bit value
shift_out(DIN, CLK, MSBFIRST, 4, v);
v = shift_in(DOUT, CLK, MSBPOST, 10);
high(CS);
return v;
}


Dave

iseries

You have to use the MCP3002 function and not the MCP3204. My unit is a 12 bit version of the 3002 which is a 10 bit version. This effects the value returned by the device.

MCP3204 can return a value between 0 and 4096 (2^12)
MCP3002 can return a value between 0 and 1024 (2^10)

So the shift function it trying to return 12 bits instead of 10 for your unit. Also MCP3204 has a different select sequence so the bits returned will be shifted.

Using the MCP3002 function it should work correctly.

int main()
{
  lcd = serial_open(12, 12, 0, 9600); //Pin12 out,pin12 in,data bits 0,baud rate 9600
  
  writeChar(lcd, ON);
  writeChar(lcd, BLTON);
  
  input(DOUT);
  
  low(CS);
  high(CS);
  

  while (1)
  {
    i = readMCP3002(0);
    print("Value: %d\n", i);
    writeChar(lcd, ON);
    writeChar(lcd, CLR);
    i = readMCP3002(0);
    n = i;
    n = n / 10;
    dprint(lcd, "Volts: %d", n);
    pause(1000);
  }      
}

Also you defined n as an integer so there is no decimal digits. So 1/10 = 0 where as if you use float it would return 0.1 as a value.

Mike