74LS138 Mux with two potentiometers (AD5206)

Forum 2005-2010 (read only) Hardware Troubleshooting
1

Question about Potentiometers and Arduino ...

2

Hi,

I am using an Arduino Duemilanove with a MuxShield to design a device that measures the intensity of 9 lasers using 9 IC photodiodes:

photoDiodes: (http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=296-23090-5-ND)

Mux Shield: (Mux Shield | Mayhew Labs)

I am also using potentiometers (AD5206) to control the intensity of the lasers ... Since the AD5206 can only control up to 6 lasers at a time, I need to use a 3-to-8 line decoder or multiplexer to toggle between the two potentiometers.

I am able to use just a single potentiometer (directly connected with the Mux Shield without using a decoder) and operate 6 lasers however when I try to use the decoder and have two potentiometers work at the same time I am having difficulties. I am not quite sure if it is the programming or the just the wiring of the decoder but I am unable to sort it out ... The code I am trying to use for the two potentiometers with the decoder is as follows:

#define CONTROL0 5 //MUX control pin 0 (S3 is connected to Arduino pin 2)
#define CONTROL1 4
#define CONTROL2 3
#define CONTROL3 2

#define DATAOUT 9 //MOSI
#define SPICLOCK 8 //sck
#define DATAIN 12 //MISO - not used, but part of builtin SPI

#define AONE 13 //73LS138 - A0
#define ATWO 11 //73LS138 - A1
#define SLAVESELECT 10 //73LS138 - A2
#define E3 6

//byte pot=0;
byte data_counter=0;
byte resistance=0;

int pause = 500; // The higher the number, the slower the timing.
int mux2array[8];
int num[8];
float calc[8];

float SCALE = 4.8828125; // Conversion from 0-1023 to 0-5V
int ptime = 0;

char spi_transfer(volatile char data)
{
SPDR = data; // Start the transmission
while (!(SPSR & (1<<SPIF))) // Wait the end of the transmission
{
};
return SPDR; // return the received byte
}

void setup()
{
byte i;
byte clr;

pinMode(CONTROL0, OUTPUT); // Set MUX control pins to output
pinMode(CONTROL1, OUTPUT);
pinMode(CONTROL2, OUTPUT);
pinMode(CONTROL3, OUTPUT);

pinMode(14, OUTPUT);
pinMode(15, INPUT);
pinMode(16, OUTPUT); // Turn on output to digital pins 14 & 16 (MUX 1 & 2) and turn off the other multiplexer data pin

pinMode(DATAOUT, OUTPUT);
pinMode(DATAIN, INPUT);
pinMode(SPICLOCK,OUTPUT);

pinMode(SLAVESELECT,OUTPUT);
pinMode(AONE, OUTPUT);
pinMode(ATWO, OUTPUT);

pinMode(E3, OUTPUT);
// digitalWrite(SLAVESELECT,HIGH); //disable device

// SPCR = 01010000
//interrupt disabled,spi enabled,msb 1st,master,clk low when idle,
//sample on leading edge of clk,system clock/4 (fastest)

SPCR = (1<<SPE)|(1<<MSTR);
clr=SPSR;
clr=SPDR;
delay(10);

for (i=0;i<6;i++)
{
write_pot1(i,255);
write_pot2(i,255);
}
Serial.begin(9600);
Serial.println();
Serial.print("TURBIDITY MEASUREMENTS");
Serial.println();
Serial.println();
Serial.print("Time (s)\t1 - 6.50 (mV)\tTime (s)\t2 - 5.10(mV)\tTime (s)\t3 - 3.70(mV)\tTime (s)\t4 - 2.20 (mV)\tTime (s)\t5 - 0.80 (mV)\tTime (s)\t6 - 6.00 (mV)\tTime (s)\t7 - 4.50 (mV)\tTime (s)\t8 - 3.00 (mV)\tTime (s)\t9 - 1.50 (mV)");
Serial.println();
}

byte write_pot1(int pot1, int value1)
{
digitalWrite(AONE, LOW);
digitalWrite(ATWO, LOW);
digitalWrite(SLAVESELECT,LOW); //2 byte opcode
spi_transfer(pot1);
spi_transfer(value1);
digitalWrite(AONE, HIGH);
digitalWrite(ATWO,HIGH);
digitalWrite(SLAVESELECT,HIGH); //release chip, signal end transfer
}

byte write_pot2(int pot2, int value2)
{
digitalWrite(AONE, HIGH);
digitalWrite(ATWO, LOW);
digitalWrite(SLAVESELECT,LOW); //2 byte opcode
spi_transfer(pot2);
spi_transfer(value2);
digitalWrite(AONE, HIGH);
digitalWrite(ATWO,HIGH);
digitalWrite(SLAVESELECT,HIGH); //release chip, signal end transfer
}

byte record_data(int a)
{
digitalWrite(CONTROL0, (a&15)>>3); //S3
digitalWrite(CONTROL1, (a&7)>>2); //S2
digitalWrite(CONTROL2, (a&3)>>1); //S1
digitalWrite(CONTROL3, (a&1)); //S0

delay(pause);
mux2array[a] = analogRead(1);
calc[a] = mux2array[a]*SCALE;
num[a] = (int)calc[a];
Serial.print(ptime);
ptime = ptime + 1;
Serial.print("\t");
Serial.print(num[a]);
Serial.print("\t");
delay(pause);
}

void loop()
{
write_pot1(0, 0);
record_data(data_counter);
write_pot1(0, 255);
data_counter++;

write_pot1(1, 0);
record_data(data_counter);
write_pot1(1, 255);
data_counter++;

write_pot1(2, 0);
record_data(data_counter);
write_pot1(2, 255);
data_counter++;

write_pot1(3, 0);
record_data(data_counter);
write_pot1(3, 255);
data_counter++;

write_pot1(4, 0);
record_data(data_counter);
write_pot1(4, 255);
data_counter++;

write_pot1(5, 0);
record_data(data_counter);
write_pot1(5, 255);
data_counter++;

write_pot2(1, 0);
record_data(data_counter);
write_pot2(1, 255);
data_counter++;

write_pot2(2, 0);
record_data(data_counter);
write_pot2(2, 255);
data_counter++;

write_pot2(3, 0);
record_data(data_counter);
write_pot2(3, 255);
data_counter++;

data_counter=0;
Serial.println();
}

If someone could kindly help me with this problem, that would be wonderful ... Thanks for your help!

Varun

3

Do you have some kind of "for" loop allergy?

When posting code, can you please use the "#" button on the editor's toolbar? (just next to the printer symbol)

I am having difficulties

You haven't explained what these might be.

4

Hi AWOL,

Thanks for the reply and sorry for the inconvenience. The reason I did not use "for" loops (in void loop) is because I wanted to change the intensity of each individual laser depending on the calibration of my system. I know they are all set to "0" and "255" but eventually the zeros will be different values.

Sorry for not putting "#", I am new to the board and I did not know this. Regarding the difficulties:

When I use this program with my setup, I only see the first two lasers on each potentiometer light up and then stay on forever. According the program, I should see the lasers alternate (turn on and off). Therefore, when I use the decoder to select the first potentiometer ... the lasers that are connected to the first potentiometers should start blinking in sequence from 1-6. The decoder should then switch to the second potentiometer and similarly lasers connected to the second potentiometer should start alternating. I hope I am a little better in explaining this time.

I will attach the code for you one more time:

#define CONTROL0 5                                         //MUX control pin 0 (S3 is connected to Arduino pin 2)
#define CONTROL1 4
#define CONTROL2 3
#define CONTROL3 2

#define DATAOUT 9                                         //MOSI
#define SPICLOCK 8                                        //sck
#define DATAIN 12                                         //MISO - not used, but part of builtin SPI

#define AONE 13                                           //73LS138 - A0
#define ATWO 11                                           //73LS138 - A1
#define SLAVESELECT 10                                    //73LS138 - A2
#define E3 6

//byte pot=0;
byte data_counter=0;
byte resistance=0;

int pause = 500;                                           // The higher the number, the slower the timing.
int mux2array[8];
int num[8];
float calc[8];

float SCALE = 4.8828125;                                   // Conversion from 0-1023 to 0-5V
int ptime = 0;

char spi_transfer(volatile char data)
{
  SPDR = data;                                             // Start the transmission
  while (!(SPSR & (1<<SPIF)))                              // Wait the end of the transmission
  {
  };
  return SPDR;                                             // return the received byte
}

void setup()
{
  byte i;
  byte clr;
  
  pinMode(CONTROL0, OUTPUT);                               // Set MUX control pins to output
  pinMode(CONTROL1, OUTPUT);
  pinMode(CONTROL2, OUTPUT);
  pinMode(CONTROL3, OUTPUT);
  
  pinMode(14, OUTPUT); 
  pinMode(15, INPUT);
  pinMode(16, OUTPUT);                                    // Turn on output to digital pins 14 & 16 (MUX 1 & 2) and turn off the other multiplexer data pin

  pinMode(DATAOUT, OUTPUT);
  pinMode(DATAIN, INPUT);
  pinMode(SPICLOCK,OUTPUT);

  pinMode(SLAVESELECT,OUTPUT);
  pinMode(AONE, OUTPUT);
  pinMode(ATWO, OUTPUT);
  
  pinMode(E3, OUTPUT);
//  digitalWrite(SLAVESELECT,HIGH);                         //disable device
  
  // SPCR = 01010000
  //interrupt disabled,spi enabled,msb 1st,master,clk low when idle,
  //sample on leading edge of clk,system clock/4 (fastest)
  
  SPCR = (1<<SPE)|(1<<MSTR);
  clr=SPSR;
  clr=SPDR;
  delay(10);
  
  for (i=0;i<6;i++)
  {
    write_pot1(i,255);
    write_pot2(i,255);
  }
  Serial.begin(9600);
  Serial.println();
  Serial.print("TURBIDITY MEASUREMENTS");
  Serial.println();
  Serial.println();
  Serial.print("Time (s)\t1 - 6.50 (mV)\tTime (s)\t2 - 5.10(mV)\tTime (s)\t3 - 3.70(mV)\tTime (s)\t4 - 2.20 (mV)\tTime (s)\t5 - 0.80 (mV)\tTime (s)\t6 - 6.00 (mV)\tTime (s)\t7 - 4.50 (mV)\tTime (s)\t8 - 3.00 (mV)\tTime (s)\t9 - 1.50 (mV)");
  Serial.println();
}
  
byte write_pot1(int pot1, int value1)
{
  digitalWrite(AONE, LOW);
  digitalWrite(ATWO, LOW);
  digitalWrite(SLAVESELECT,LOW);                           //2 byte opcode
  spi_transfer(pot1);
  spi_transfer(value1);
  digitalWrite(AONE, HIGH);
  digitalWrite(ATWO,HIGH);
  digitalWrite(SLAVESELECT,HIGH);                          //release chip, signal end transfer
}

byte write_pot2(int pot2, int value2)
{
  digitalWrite(AONE, HIGH);
  digitalWrite(ATWO, LOW);
  digitalWrite(SLAVESELECT,LOW);                           //2 byte opcode
  spi_transfer(pot2);
  spi_transfer(value2);
  digitalWrite(AONE, HIGH);
  digitalWrite(ATWO,HIGH);
  digitalWrite(SLAVESELECT,HIGH);                          //release chip, signal end transfer
}

byte record_data(int a)
{
  digitalWrite(CONTROL0, (a&15)>>3);                       //S3
  digitalWrite(CONTROL1, (a&7)>>2);                        //S2
  digitalWrite(CONTROL2, (a&3)>>1);                        //S1
  digitalWrite(CONTROL3, (a&1));                           //S0
  
  delay(pause);
  mux2array[a] = analogRead(1);
  calc[a] = mux2array[a]*SCALE;
  num[a] = (int)calc[a];
  Serial.print(ptime);
  ptime = ptime + 1;
  Serial.print("\t");
  Serial.print(num[a]);
  Serial.print("\t");  
  delay(pause);
}

void loop()
{ 
  write_pot1(0, 0);
  record_data(data_counter);
  write_pot1(0, 255);
  data_counter++;
  
  write_pot1(1, 0);
  record_data(data_counter);
  write_pot1(1, 255);
  data_counter++;
  
  write_pot1(2, 0);
  record_data(data_counter);
  write_pot1(2, 255);
  data_counter++;

  write_pot1(3, 0);
  record_data(data_counter);
  write_pot1(3, 255);
  data_counter++;

  write_pot1(4, 0);
  record_data(data_counter);
  write_pot1(4, 255);
  data_counter++;
  
  write_pot1(5, 0);
  record_data(data_counter);
  write_pot1(5, 255);
  data_counter++;

  write_pot2(1, 0);
  record_data(data_counter);
  write_pot2(1, 255);
  data_counter++;

  write_pot2(2, 0);
  record_data(data_counter);
  write_pot2(2, 255);
  data_counter++;

  write_pot2(3, 0);
  record_data(data_counter);
  write_pot2(3, 255);
  data_counter++;

  data_counter=0;
  Serial.println();
}

I hope this helps.

Thanks,
Varun

5 
for (int i = 0; i < N_LASERS; ++i) {
  write_pot( pot [i], laser [i], calValue [i][0]);
  record_data(data_counter);
  write_pot( pot [i], laser [i], calValue [i][1]);
  data_counter++;
}

This way, you can vary the value of "N_LASERS" and get things to work, and your tables "pot", "laser" and "calValue" can all be defined in one place.

6

Can you post a schematic please. My concern is that a 74LS138 is a digital chip and I would not expect it to be used in this situation.

7

Hi Admins,

Actually, I figured it out. I am now using a "hex Inverter" to switch between the potentiometers. It does work because I only have two pots.

Thanks for your help

Varun

8

To switch between potentiometers that are analog pieces, you should use an analog multiplexer like 4051 for example.
Look here for an explanation Arduino Playground - 4051