Digital Control of Fiber Coupled Laser Diode

Developing a new digital circuit using a micro-controller to drive Laser (LED1) replacing analog methods of curent control.

The Existing circuit we are trying to reeplicate digitally:

Some of our objectives :-

• Controlling the current to a LASER thorugh digital means instead of analog means (Variable Resistors)
• Reading the current drawn and power of the LASER dynamicvally using INA219 Current Sensor
• Interfacing an LCD to monitor the display the PWM value of micro-controller and the curreent and poweer drawn dynamically

Additional improvent and additions

• Adding a temperature sensor to measure the ambient temperature
• Adding a bluetooth transreciever to control the curreent value remotely
• Developing an app or webpage based GUI application
• Logging all the data recieved and store it on sd card or cloud
• Housing all the electronics in a approprite housing.

Prototyping the existing circuit

Made the circuit following the schematic to drive the LASER

code snippet of sending increased PWM signals through A9 pin of Arduino

void loop() {
     analogWrite(9,100);                                           // Laser diode connected to pin A9
     delay(1000);
     analogWrite(9,150);
     delay(1000);
     analogWrite(9,200);
     delay(1000);
     analogWrite(9,250);
     delay(1000);
     analogWrite(9,0);
     delay(1000);
}

Intefaced the LCD to show any required data

Code with LCD initialsed:

// include the library code:

#include <LiquidCrystal.h>                                     // initialize the library by associating any needed LCD interface pin

const int rs = 12, en = 11, d4 = 5, d5 = 4, d6 = 3, d7 = 2;    // with the arduino pin number it is connected to

LiquidCrystal lcd(rs, en, d4, d5, d6, d7);

void setup() {                                                 // set up the LCD's number of columns and rows:

lcd.begin(16, 2);

}

void loop() {
 analogWrite(9,100);                                           // Laser diode connected to pin A9
 delay(1000);
 analogWrite(9,150);
 delay(1000);
 analogWrite(9,200);
 delay(1000);
 analogWrite(9,250);
 delay(1000);
 analogWrite(9,0);
 delay(1000);

                                                           // LCD Message
lcd.print("   HELLO       ");
lcd.setCursor(0,1);                                        // Set the cursor for the second line( the second 1 after comma sets the cursor at the 2 or lower line).
lcd.print("      WORLD "); 

}

Interfaced the INA219 Current sensor to measure the current value

The vale from the INA219 using the LCD's LED as load :) (As I am doing this project Hochschule, I am quite restricted with parts)

Code for inteerfacing INA219 and measuring the current values

#include <Wire.h>
#include <Adafruit_INA219.h>

Adafruit_INA219 ina219;

void setup(void) 
{
  Serial.begin(9600);
  while (!Serial) {
      // will pause Zero, Leonardo, etc until serial console opens
      delay(1);
  }

  uint32_t currentFrequency;

  Serial.println("Hello!");

  if (! ina219.begin()) {
    Serial.println("Failed to find INA219 chip");
    while (1) { delay(10); }
  }

  Serial.println("Measuring voltage and current with INA219 ...");
}

void loop(void) 
{
  float shuntvoltage = 0;
  float busvoltage = 0;
  float current_mA = 0;
  float loadvoltage = 0;
  float power_mW = 0;

  shuntvoltage = ina219.getShuntVoltage_mV();
  busvoltage = ina219.getBusVoltage_V();
  current_mA = ina219.getCurrent_mA();
  power_mW = ina219.getPower_mW();
  loadvoltage = busvoltage + (shuntvoltage / 1000);

  Serial.print("Bus Voltage:   "); Serial.print(busvoltage); Serial.println(" V");
  Serial.print("Shunt Voltage: "); Serial.print(shuntvoltage); Serial.println(" mV");
  Serial.print("Load Voltage:  "); Serial.print(loadvoltage); Serial.println(" V");
  Serial.print("Current:       "); Serial.print(current_mA); Serial.println(" mA");
  Serial.print("Power:         "); Serial.print(power_mW); Serial.println(" mW");
  Serial.println("");

  delay(2000);
}

Schematic for the entire plan and existing circuits which are already implemented, we can futher make the system more compact using an on-board ATMEGA328 IC.

We plan to use MCP4725 to convert the analog PWM signals from Arduino to digital values then use that to drive a current controlled Op-amp circuit in a voltage followeer mode.

Some of my simulations :-

and then use a HM10 Blueetooth module to control the system oveer bluetooth remotely.