Arduino work on reading ALDL 160 baud data A resource I found useful for exploring more about ALDL: https://www.techedge.com.au/vehicle/aldl160/aldl_sw.htm
Arduino NANO, NPN transaitor, 10k resistor
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Digital pin 2 connected to collector of transistor (configured with internal pullup resistor)
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Base of transitor connect to ALDL port E with a resistor in series
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Ground connected to Emiter of transistor, ALDL port A, and ground of the Arduino.
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Optionally add an I2C header connected to 5V, GDN, A4 & A5 to attach a display.
Quick summary:
- Attach an interrupt to pin 2 on change
- If LOW (inverted by transitor) then note millis
- If HIGH, compare duration between change. < 2000us = 0; >2000us = 1
- Assemble bits into 9 bit bytes.
- 0x1FF (9 1s in a row) is the sync character
- Data until next sync is messages in format 0x0XX where XX is a data message per the ECM spec
IN PROGRESS
I have a 1990 GMC with a 5V 160 baud ALDL diagnostics port. After receiving a "service engine" light I set out the path of building a USB cable and using WinALDL (https://winaldl.joby.se/) to diagnose what was going on. (Code 32, EGR, had to replace a solenoid). After exploring the data in WinALDL I realized RPM and speed was reported by the ECM and I thought that would be useful display. I have a bunch of Arduinos and ESP32s kicking around and several 1602 and OLED displays.... I figured I must be able to connect a ucontroller to the data pin and extract that data on a display in near real-time.
I studied lots of source code repos and websites for inspiration:
- https://www.bot-thoughts.com/2018/01/decoding-gms-aldl-with-teensy-36.html
- https://www.techedge.com.au/vehicle/aldl160/aldl_sw.htm
- https://github.com/rchipka/Arduino-ALDL-160-baud
- https://github.com/MikeEckels/OBD1Scanner/tree/master/OBD1Scanner
- https://github.com/MikeEckels/OBD1Scanner/blob/master/OBD1Scanner/DataStreamDefs.h
- https://github.com/shimniok/ALDL160_logger
- https://winaldl.joby.se/aldlcable.htm