From 619ec20ca1db6dd914e10788451edda657cc8734 Mon Sep 17 00:00:00 2001 From: gronod Date: Fri, 12 Jun 2026 07:54:48 +0100 Subject: [PATCH] Add README.md --- README.md | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 55 insertions(+) create mode 100644 README.md diff --git a/README.md b/README.md new file mode 100644 index 0000000..594a464 --- /dev/null +++ b/README.md @@ -0,0 +1,55 @@ +# ESP32 ALDL Wireless Bridge + +**ESP32 firmware for reading GM 160-baud PWM ALDL data from a 1986–1988 Pontiac Fiero 2.8L V6 (1227170 ECM) and streaming it wirelessly over Bluetooth SPP.** + +This project turns an ESP32 into a reliable, low-latency wireless ALDL interface. It decodes the raw 160-baud PWM signal in real time and forwards clean 25-byte data frames over Bluetooth to the companion Android app ([esp32-aldl-android](https://git.i3omb.com/gronod/esp32-aldl-android)). + +--- + +## Features + +- **Real-time 160-baud PWM ALDL decoding** — Custom bit-banged decoder running in a high-priority FreeRTOS task +- **Robust pulse handling** — Handles glitches, merged pulses, and idle gaps gracefully +- **Hard frame synchronization** — Prepends `0xAA 0x55` header for reliable packet alignment on the receiving side +- **Bluetooth SPP (Serial Port Profile)** — Appears as a classic Bluetooth serial device named `ESP32-ALDL` +- **Decoupled architecture** — ISR → Ring buffer → Decoder task → Bluetooth transmit queue +- **Status reporting** — Periodic status output over USB serial +- **Low CPU usage** on the decoder core while maintaining timing accuracy + +--- + +## Supported Hardware + +- **ECM**: GM 1227170 (1986–1988 Pontiac Fiero 2.8L V6) +- **ALDL Mode**: `$24` / `$24A` mask (25-byte continuous broadcast frames) +- **Microcontroller**: ESP32 (any dev board with sufficient GPIO — tested on ESP32-WROOM-32 and ESP32-S3) +- **Bluetooth**: Classic Bluetooth (BR/EDR) — works with most Android devices + +--- + +## Pin Connections + +| Signal | ESP32 Pin | Notes | +|--------------|---------------|--------------------------------------------| +| ALDL Data In | **GPIO 4** | Connect to ALDL pin **M** (data line) | +| GND | GND | Must share ground with the car/ECU | +| 5V / 3.3V | — | **Do not** power the ESP32 from the ALDL line | + +> **Important**: The ALDL line is a 5V PWM signal. The ESP32 GPIO is 3.3V tolerant for input in most cases, but a simple voltage divider or level shifter (e.g., 1kΩ + 2kΩ) is recommended for long-term reliability. + +--- + +## How It Works + +### Signal Decoding +The firmware uses an interrupt service routine (ISR) triggered on any edge of GPIO 4. Pulse widths are measured using the ESP32 high-resolution timer and pushed into a lock-free ring buffer. + +A dedicated decoder task (`aldlDecodeTask`) processes the pulse stream: + +- Classifies pulses as `0`, `1`, glitch, merged pulse, or idle gap +- Reconstructs bytes using the standard 160-baud ALDL PWM encoding +- Assembles complete 25-byte frames +- Validates and enqueues valid frames + +### Bluetooth Transmission +A separate task (`btTransmitTask`) pulls decoded frames from a FreeRTOS queue and transmits them over Bluetooth SPP with a 2-byte hard sync header: \ No newline at end of file