Circuit Implementation of Phase Shift Keying (PSK) modulation

Phase Shift Keying (PSK) is a popular digital modulation technique widely used in wireless communication systems. Among its variations, Binary Phase Shift Keying (BPSK) is the simplest form, where the phase of a carrier signal is shifted based on digital data input. In this article, we will walk you through the process of implementing a BPSK modulation circuit using an Arduino microcontroller. This guide will cover the components needed, circuit design, Arduino code, and practical implementation. For those interested in exploring more about signal generation and modulation using Arduino, we recommend checking out our guides on Arduino AM radio receiver and Arduino DDS (Direct Digital Synthesis).

Understanding BPSK Modulation

Binary Phase Shift Keying (BPSK) is a digital modulation technique where the phase of a constant-frequency carrier signal is changed according to the binary data being transmitted. When the input bit is "1," the carrier signal is in phase; when the input bit is "0," the carrier signal is shifted by 180 degrees (out of phase). This method is efficient and has good noise immunity, making it suitable for various communication systems.

Components Required

To build a BPSK modulator circuit using an Arduino, you will need the following components:

1. Arduino Uno or any compatible board
2. AD633 or MC1496 IC - For mixing the carrier and data signals.
3. Oscillator or Function Generator - To generate a carrier signal.
4. Low-Pass Filter - To filter out high-frequency noise.
5. Resistors and Capacitors - For building filters and other circuit elements.
6. Breadboard and Jumper Wires - For circuit prototyping.
7. Oscilloscope - To visualize the signals (optional but helpful).

Circuit Implementation

Below is the step-by-step process for building a BPSK modulation circuit using an Arduino:

1. Generate the Carrier Signal

The first step is to generate a carrier signal. A carrier signal is a sine wave with a constant frequency. You can use an oscillator circuit like a Colpitts oscillator or a function generator to produce a carrier wave. Alternatively, you can use an Arduino for signal generation. Refer to our article on AM transmitter using Arduino for more insights into signal generation with Arduino.

2. Generate the Digital Data Signal

The Arduino will be used to generate the digital data signal, typically a square wave at a much lower frequency than the carrier signal. This digital data represents binary "0" and "1" bits for the modulation process.

3. Mix the Carrier and Data Signals

Use a balanced mixer or multiplier IC, such as the AD633 or MC1496, to mix the carrier and digital data signals. Connect the carrier signal to one input of the IC and the digital data signal to the other input. The output from the mixer will be a BPSK modulated signal.

4. Filter the Output Signal

After mixing, pass the output signal through a low-pass filter to remove high-frequency noise and obtain a clean BPSK modulated signal.

5. Amplify the Signal (Optional)

If the output signal strength is low, you can amplify it using an operational amplifier (e.g., LM358). Proper amplification is crucial for transmission in a communication system.

Circuit Diagram

Below is a simplified circuit diagram for a BPSK modulator:

Arduino Code for BPSK Modulation

The following Arduino code will generate a digital data signal and modulate it using a square wave carrier signal. You can adjust the frequency of the carrier and data signals to suit your requirements:

const int dataPin = 9;     // Data signal output pin
const int dataFrequency = 10;  // Data signal frequency in Hz (10 Hz)

void setup() {
  pinMode(dataPin, OUTPUT);
}

void loop() {
  generateDataSignal();
}

void generateDataSignal() {
  static unsigned long lastChangeTime = 0;
  static bool dataState = LOW;
  
  if (millis() - lastChangeTime >= (1000 / dataFrequency) / 2) {  // Half-period of the data frequency
    dataState = !dataState;  // Toggle data state
    digitalWrite(dataPin, dataState);  // Output the data signal
    lastChangeTime = millis();
  }
}

6. Testing and Verification

To verify the output, use an oscilloscope to observe the modulated BPSK signal. Adjust the frequency of the carrier and data signals to see how the phase shifts in the waveform correspond to the binary data. You can also use a frequency counter circuit like the one described in our guide on high-frequency counter with Arduino to monitor the carrier frequency.