scottlittle scottlittle - 3 months ago 6
C Question

Multiple analog to digital converters on Arduino using SPI bit banging

I am using a Nano Arduino (ATMega 328) to communicate to two 12-bit MCP3208 ADC chips based on this code. I have another device (LED driver TLC5940) tied to the pins that are suggested on this page but since I am using bit banging, it should not matter what pins I use. So, my configuration is the same as the above example except that:

For ADC 1:
CLK -> Arduino D6
DOUT (MISO) -> Arduino D5
DIN (MOSI) -> Arduino D12
SS -> Arduino D7

For ADC 2:
CLK -> Arduino D6
DOUT (MISO) -> Arduino D5
DIN (MOSI) -> Arduino D12
SS -> Arduino D8


So, the problem is that I get data from ADC 1 but not from ADC 2. I should be able to select ADC 2 by by pulling the selection pin low but all I get is 0. There are 16 photodiodes connected to 4 TLC2274 op-amps. Here is the Arduino code:

//Scott Little, BrainGoggles, 2013, GNU GPL v3
#include <SoftwareSerial.h>
#include "Tlc5940.h"
SoftwareSerial bluetooth(4,2); //TX 4, RX 2

#define SELPIN 7 //Selection Pin for 1st ADC
#define SELPIN2 8 //Selection Pin for 2nd ADC
#define DATAOUT 12//MOSI
#define DATAIN 5//MISO
#define SPICLOCK 6//Clock
int readvalue;
byte readvaluearray[32];
int intensity = 0;

void setup()
{
/* Call Tlc.init() to setup the tlc.
You can optionally pass an initial PWM value (0 - 4095) for all channels.*/
Tlc.init(); //interferes with other SPI
Tlc.clear(); //set pin modes

pinMode(SELPIN, OUTPUT); //adc 1 selection pin
pinMode(SELPIN2, OUTPUT); //adc 2 selection pin
pinMode(DATAOUT, OUTPUT);
pinMode(DATAIN, INPUT);
pinMode(SPICLOCK, OUTPUT);
//disable devices to start with
digitalWrite(SELPIN,HIGH);
digitalWrite(SELPIN2,HIGH);
digitalWrite(DATAOUT,LOW);
digitalWrite(SPICLOCK,LOW);
bluetooth.begin(9600);
Serial.begin(9600);

}

void loop()
{
if (bluetooth.available()) // Wait until a character is received
{
char val = (char)bluetooth.read();
Serial.println(val);

switch(val) // Perform an action depending on the command
{
case 't'://increase intensity when an 'e' is received
intensity = plus(intensity);
break;

case 'y'://decrease intensity when an 'r' is received
intensity = minus(intensity);
break;

case 'q'://turn the light on when a 'q' is received
on();
break;

case 'w'://turn the light off when a 'w' is received
off();
break;
}
}

for (int i=0; i<8; i++){ //read from ADC 1
readvalue = read_adc(i+1);
readvaluearray[2*i] = highByte(readvalue);
readvaluearray[2*i+1] = lowByte(readvalue);
}

for (int i=8; i<16; i++){ //read from ADC 2
readvalue = read_adc2(i-7);
readvaluearray[2*i] = highByte(readvalue);
readvaluearray[2*i+1] = lowByte(readvalue);
}

bluetooth.write(readvaluearray,32);
Serial.println("new");
for (int i=0;i<16;i++){
Serial.println(word(readvaluearray[2*i],readvaluearray[2*i+1]));
}

delay(2000);
}


int read_adc(int channel){
int adcvalue = 0;
byte commandbits = B11000000; //command bits - start, mode, chn (3), dont care (3)

//allow channel selection
commandbits|=((channel-1)<<3);

digitalWrite(SELPIN,LOW); //Select adc

// setup bits to be written
for (int i=7; i>=3; i--){
digitalWrite(DATAOUT,commandbits&1<<i);
//cycle clock
digitalWrite(SPICLOCK,HIGH);
digitalWrite(SPICLOCK,LOW);
}

digitalWrite(SPICLOCK,HIGH); //ignores 2 null bits
digitalWrite(SPICLOCK,LOW);
digitalWrite(SPICLOCK,HIGH);
digitalWrite(SPICLOCK,LOW);

//read bits from adc
for (int i=11; i>=0; i--){
adcvalue+=digitalRead(DATAIN)<<i;
//cycle clock
digitalWrite(SPICLOCK,HIGH);
digitalWrite(SPICLOCK,LOW);
}
digitalWrite(SELPIN, HIGH); //turn off device

return adcvalue;
}

int read_adc2(int channel){
int adcvalue = 0;
byte commandbits = B11000000; //command bits - start, mode, chn (3), dont care (3)

//allow channel selection
commandbits|=((channel-1)<<3);

digitalWrite(SELPIN2,LOW); //Select adc

// setup bits to be written
for (int i=7; i>=3; i--){
digitalWrite(DATAOUT,commandbits&1<<i);
//cycle clock
digitalWrite(SPICLOCK,HIGH);
digitalWrite(SPICLOCK,LOW);
}

digitalWrite(SPICLOCK,HIGH); //ignores 2 null bits
digitalWrite(SPICLOCK,LOW);
digitalWrite(SPICLOCK,HIGH);
digitalWrite(SPICLOCK,LOW);

//read bits from adc
for (int i=11; i>=0; i--){
adcvalue+=digitalRead(DATAIN)<<i;
//cycle clock
digitalWrite(SPICLOCK,HIGH);
digitalWrite(SPICLOCK,LOW);
}
digitalWrite(SELPIN2, HIGH); //turn off device

return adcvalue;
}

void on(void)
{
Tlc.set(1, 4095); //set pin 5 to max brightness
Tlc.update(); //execute set
//bluetooth.println("on");
//Serial.println("on");
}

void off(void)
{
Tlc.set(1, 0); //set pin 5 to min brightness
Tlc.update(); //execute set
//bluetooth.println("off");
//Serial.println("off");
}

int plus(int value)
{
value = value + 64;
if (value > 4095){value = 4095;}
Tlc.set(1, value); //set pin 5 to min brightness
Tlc.update(); //execute set
Serial.println(value);
return value;
}

int minus(int value)
{
value = value - 64;
if (value < 0){value = 0;}
Tlc.set(1, value); //set pin 5 to min brightness
Tlc.update(); //execute set
Serial.println(value);
return value;
}


Here is sample output that I am getting:

new
374
372
311
313
356
276
337
387
0
0
0
0
0
0
0
0

Answer

It is working now. I physically changed the pin on the ADC corresponding to DOUT (ADC 12) to the pin on the Arduino corresponding to MISO (Arduino 12) and changed the code as such:

#define DATAOUT 5  //MOSI 
#define DATAIN  12 //MISO 

It should have worked as I had it before since I am bit banging, but it seems to work now as MISO is on the "correct" pin.