Steps to develop a cheap ESP32-based ARINC 429 reader using two optocouplers for bit-banged reception + a simple web page for text output.

1. Understand the signal and safety constraints

• Differential levels (A – B):
  • Logic 1 (HI): ~+6.5 V to +13 V
  • NULL: ~–2.5 V to +2.5 V
  • Logic 0 (LO): ~–6.5 V to –13 V

2. Hardware design (cheap discrete front-end)

• Series current-limiting resistors (a few mA).
•  series protection resistors + TVS diodes or clamping for transient robustness.
• Two optocouplers6N137 / TLP2361 / similar high-speed optos if you target 100 kbps).
• On the ESP32 side: pull-ups (external 4.7–10 k?)
• Power the opto output side from the ESP32 3.3 V rail; keep grounds separate (true isolation).

Sketch the circuit, calculate LED current, verify rise/fall times on a scope with a real or simulated ARINC source, and add decoupling. Keep the analog/high-voltage side physically separated from the digital side.

Alternative low-cost approaches (if pure optos prove too slow or awkward): discrete comparators (e.g., LM393 or better) followed by digital isolators, or the op-amp + logic circuits used in some open ESP32 ARINC boards. Stick to two optos if that is the design goal.

3. ESP32 platform and pinout

• (dual-core is helpful).
• GPIOs for the opto outputs (e.g., GPIO 18 / 19).
• Power from USB or a clean 5 V ? 3.3 V regulator.
• Optional: status LEDs, a small display, or Ethernet if Wi-Fi is unreliable.

4. Software – bit-banged receiver

Use Arduino-ESP32 or ESP-IDF + FreeRTOS.

High-level approach:

• Configure the two GPIOs as inputs with pull-ups.
• Use pin-change / edge interrupts (or a high-priority FreeRTOS task + polling) to capture transitions on either line.
• Measure pulse widths with micros() or a hardware timer.
• State machine that recognizes:
  – Start of a word (first HI or LO pulse after a long NULL gap).
  – Each bit: first half active (HI = 1, LO = 0), second half NULL.
  – End of word after 32 bits + inter-word gap.
• Assemble the 32-bit word (label is bits 1–8, usually octal; data, SDI, SSM, parity).
• Check odd parity (bit 32).
• Buffer received words (circular queue or FreeRTOS queue) so the web server can read them without blocking the decoder.
• Optionally auto-detect speed by measuring bit period, or hard-code 12.5 / 100 kbps.
• Run the decoder on one core; keep Wi-Fi / web server on the other.

Start simple: capture raw HI/LO events and print timings to Serial. Then add word assembly and label filtering.

5. Web interface for simple text output

• Use the built-in WebServer or better ESPAsyncWebServer (non-blocking).
• Create an Access-Point mode or join an existing Wi-Fi network.
• Serve a minimal HTML page (plain text or a simple table) that:
  – Shows the latest words (label in octal, raw hex, decoded fields if you implement a basic BNR/BCD parser).
  – Optionally auto-refreshes via meta-refresh or a tiny JavaScript fetch every second.
• Optional: WebSocket for live streaming of new words.

6. Development and test sequence

1. inject known ±5–10 V
2. Write a minimal interrupt logger that timestamps every edge.
3. refine the timing state machine until you reliably get 32-bit words with correct parity.
4. Add the web server and confirm the page updates.
5. Stress-test with continuous traffic, noise, and both speeds.
6. Add basic error counters (parity fails, framing errors, gaps too short).

• Open-source references worth studying: low-cost ESP32 ARINC boards that use op-amps/logic (search “ARINC 429 TX-RX Board ESP32”), RP2040 PIO-based designs, and classic Holt HI-8588 receiver + AVR interrupt examples (the software structure is transferable).

Once the hardware front-end produces clean HI/LO digital signals, the rest is mostly careful timing and a lightweight web UI. Start with low-speed, get solid word capture on the serial console, then add the web page.

 

================================================

Here is a wonderfull 429 overview

429commentary

airinc_429TheAvionicsHandbook_Cap_2

 

https://batchpcb.com/pcbs/73951 ia a universal converter project.

 

The fellows name is AllThumbs on VAF http://www.vansairforce.com/community/showthread.php?t=95229

 

http://www.vansairforce.com/community/archive/index.php?t-82604.html thread about the SL30 to Dynon HSI

 

 

http://www.instructables.com/id/Interfacing-Electronic-Circuits-to-Arduinos/ is a very nice explanation of a 429 to 232 converter

Here is the data from Niel on the frankenverter

FrankenVerterInitialFiles.tar

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

here is a nice blurb on using a parallel port to test AIRINC 429 equipment

testing429WithPC

 

here is some detail abouthe labels

Arinc429WordList (copy)

Here is the first Distillation of equipment labels

Labels

 

=============================================

2024 revival project

https://github.com/ncormia/FrankenVerter

https://github.com/ncormia/FrankenVerter/blob/master/a429.h

https://github.com/ncormia/FrankenVerter/blob/master/FrankenVerter.ino

 

Explanation with scope

 

 

 

r to left

Dewalt Lion , batteries in a Quart can for containment

screwdriver tips

velcro, tywrap, tape

saw

crush proof container, magnet, fingers, mirror

3/8 deep 12 points, ratchet handle

1/4 drive set

small ratchet screwdriver, large screw driver, poor quality

punch, allen, knife, measure tape

4 picks, small screwdriver, slot, phillips

file

small diagonal, visegrips,

KNIPEX needle nose, diagonal, slip joint pliers.

small combo, large gear wrench, large adjustable.

 

+++++++++++++

Arthur

Author

Q

Variable belcrank

qunitResistorValues