Junkbox IrDA to USB Cable

17.03.2026

I recently acquired an old Subgear XP10 dive computer, and wanted to be able to extract dive logs from it once I start using it. A quick investigation showed that the device supports regular IrDA, and is compatible with the modern dive log software "Subsurface". So far so good. However I also saw that IrDA is now so old that support for it is more or less removed from most operating systems, and USB dongles are difficult to come by. The few reputable dongles I could find were expensive, actually matching the price I paid for the dive computer! There is however an updated USB device available complete with great documentation, known as IrDroid. The price was somewhat off-putting though, and given that it is simply an MCP2120 chip, IR transceiver, and a USB to serial converter, I felt I could just make one myself. Of course, that would require designing and waiting for a PCB to arrive, and ordering parts, both of which take time and become rather expensive unless combined with other orders. Not exactly the low key weekend project I wanted. Some more research lead me to a forum post where people were able get IrDA working on ESP-C3 chips, with regular IR LEDs and photodiodes. Now we're getting somewhere!

I opted to use Arduino as the IDE since it was quick and easy to set up. To get the board running I followed the first part of this guide from Random Nerd Tutorials: Getting Started with the ESP32-C3 Super Mini. Essentially, install the Expressif ESP32 boards, connect the ESP32-C3 Super to the computer, do the boot process:


 Hold down boot.
 Press Reset.
 Release Boot.

Select the board type "Olimex ESP32-C3-Dev". Enable USB serial via Tools -> USB CDC on Boot.
After some trial and error I eventually got IrDA working on the ESP32-C3. None of the code examples I could find worked entirely, and the documentation for the irda struct fields in UART.conf seemed a bit off. All in all it didn't take much work to get this running though. I picked GPIO6 (RX) and GPIO7 (TX) for the IrDA pins. Here is the Arduino source code.


  // IrDA to USB Dongle
  // Eirik Taylor, 04.03.2026
  
  #include "soc/uart_struct.h"
  
  // ESP32 C3 Super Mini on-board LED. Is active LOW
  const int ledPin = 8; 
  
  HardwareSerial IrdaSerial(1);
  
  void setup()
  {
    HWCDCSerial.begin(9600); // Set up USB, remember to enable USB CDC on boot
    IrdaSerial.begin(9600, SERIAL_8N1, 6, 7); // Pick the IO pins to use
  
    UART1.conf0.irda_en = 1;        // Enable IrDA
    UART1.conf0.irda_tx_en = 1;     // Enable TX
    UART1.conf0.irda_dplx = 1;      // Enable RX
    UART1.conf0.irda_rx_inv = 0;    // RX inversion selection
    
    pinMode(ledPin, OUTPUT);
    digitalWrite(ledPin, HIGH);
  }
  
  void loop()
  {
    // IrDA transmission of USB received data
    if (HWCDCSerial.available())
    {
      digitalWrite(ledPin, LOW);
      while(HWCDCSerial.available())
      {
        IrdaSerial.write(HWCDCSerial.read());
      }
      IrdaSerial.flush();
      digitalWrite(ledPin, HIGH);
    }
  
    // USB transmission of IrDA received data
    while(IrdaSerial.available())
    {
        HWCDCSerial.write(IrdaSerial.read());
    }
  }

I was able to purchase an ESP32-C3 locally for the same cost as a TFDU4101 IR module alone, and coupled with some parts from my junkbox I quickly had a working prototype. The circuit is a simple high pass filter with adjustable threshold. The idea being that ambient IR can be filtered out, meaning the threshold can be set based on dynamic response instead, which is more static (hehe). The tuning potentiometer is used to set the sensitivity and tune the pulse width at the same time. Since I only have the one IR device to test with I'm not sure if this needs adjustment for each IrDA device or if it could be set to a fixed value. I simply placed the dive computer as far away as I could while still seeing decent pulses on the IR transistor, and then tuned the potentiometer so the threshold was roughly at this level. The use of an IR phototransistor over an photodiode was simply due to availability. The response time of the phototransistor is 15µs, which is almost as long as the entire on period for a data bit at 9600 baud. Fortunately the filtering squares up the signal nicely, and the resulting delay between input and output is negligible in terms the total dataword length, meaning duplex communication works fine. The response time and corresponding tuning mean the circuit is only really tuned to 9600 baud and no higher. I assume lower baud rates will work fine, but I haven't tested this. More range could probably be had by dumping a charged capacitor into the transmitting LED. This appears to be how the TFDU4101 works internally. As for better reception range, I assume a faster optodevice would help greatly. The response time of the PT204-6B phototransistor is so slow that the entire pulse is over before it's had time to respond.

As for actually using the device, there are a few steps required. The makers of IrDroid have made a number of useful guides for different operating systems, and provided a driver package which works with any serial based device. I'm using this on Windows 11, so this was the process I followed: Irdroid USB irDA Transceiver Driver Install for Windows 10

The short of it is:
Go to Optional Features -> View or Edit Optional Features -> Available Features -> Search for "IrDA". Add it. This will take a while.
Now download the driver package here.
Next go to device manager, Action -> Install Legacy Hardware -> Manually select from a list -> Infrared Devices -> Find the drivers from the zip file you just downloaded.
Once added, open the device's settings, and set the baud rate to 9600. Next go to Control Panel -> Infrared, and turn off Image and File transfer.
Disable image over IrDA as shown on this GitHub Gist page. IrDA irCOMM in Windows.

Testing I've done show this works in the dark and in broad daylight, so the front end is working as expected. The orientation of the device being interfaced with is important, as is mounting the IR diode and phototransistor the correct distance apart. With the Subgear XP10 I can space the units roughly 2cm - 4cm apart when tuned correctly. After the IrDA stack is installed on Windows, and the driver is ready, you still need to manually enter Device Manager and toggle the COM port unless the PC is booted with the IrDA USB adapter plugged in from the start. Once working, the dongle should blink as windows periodically scans for IrDA devices, indicating that data is being transmitted. All in all this was a fun little project, and nice to see that legacy devices can be resurrected using some modern hardware and software.

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Disclaimer: I do not take responsibility for any injury, death, hurt ego, or other forms of personal damage which may result from recreating these experiments. Projects are merely presented as a source of inspiration, and should only be conducted by responsible individuals, or under the supervision of responsible individuals. It is your own life, so proceed at your own risk! All projects are for noncommercial use only.

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