Capturing and Decoding Infrared Signals with the Bus Pirate

1. Introduction

This experiment demonstrates how to use the Bus Pirate to capture and decode IR signals. By analyzing these signals, you can understand the communication protocol of IR remotes and potentially recreate or replicate the commands.

2. Required Components

• Bus Pirate (v3.6 or later)
• IR receiver module (e.g., TSOP38238 or VS1838B)
• IR remote control (for testing)
• Connecting wires
• Computer with terminal software (e.g., PuTTY or Tera Term)

3. Wiring Setup

Connect the IR receiver to the Bus Pirate as follows:

• IR Receiver Output to MISO on the Bus Pirate
• GND on the IR receiver to GND on the Bus Pirate
• VCC on the IR receiver to the Bus Pirate’s 3.3V or 5V supply

Be sure to power the IR receiver with the correct voltage (typically 3.3V or 5V based on the receiver model).

4. Configuring the Bus Pirate for Capturing IR Signals

Open your terminal software and set up the Bus Pirate to capture IR data:

m 2

This command enters binary mode, allowing for communication in binary and capturing timing-based signals.

5. Capturing IR Signals

To capture IR signals, activate the capture mode on the Bus Pirate:

IR

Point the IR remote at the IR receiver and press a button. The Bus Pirate will capture the signal, displaying timing data that represents the high and low pulses of the IR signal.

6. Decoding the IR Signal

The captured timing data corresponds to the signal sent by the IR remote. To decode, you’ll need to identify the protocol (e.g., NEC, Sony, or RC5). Typically, IR signals contain pulses of data, with each protocol having a unique sequence of long and short pulses to represent binary data.

For example, NEC protocol uses a 38kHz frequency, with different timing patterns for binary 0 and 1:

• Start bit: 9ms HIGH, 4.5ms LOW
• Binary 1: 2.25ms HIGH, 0.56ms LOW
• Binary 0: 1.125ms HIGH, 0.56ms LOW

Analyze the timing sequence output from the Bus Pirate to determine if it matches a known protocol, then translate the binary sequence to determine the code sent by the remote.

7. Analyzing and Replicating Commands

Once you’ve decoded the signal, you can replicate it by sending the same timing pattern with the Bus Pirate to control the device. Use the pwm command in binary mode to create the IR signal pulses according to the decoded timing.

Example command to generate a 38kHz PWM signal:

pwm 38000, 50

Adjust pulse widths to match the timing sequence of your IR protocol.

8. Troubleshooting Tips

• No Signal Detected: Verify the wiring and ensure the IR receiver is correctly powered.
• Signal Noise: If there’s noise, try adding a small capacitor (e.g., 10µF) across VCC and GND of the IR receiver.
• Unknown Protocol: Check common IR protocols (e.g., NEC, RC5) or look for manufacturer-specific protocol documentation.

9. Conclusion

Capturing and decoding IR signals with the Bus Pirate allows you to explore IR protocols and create custom IR-controlled solutions. Once you understand the protocol, you can replicate or modify commands for new applications.