MX5 Arduino Diagnostics

A small project to read the blink codes from an 89-95 Mazda MX5 diagnostic port and display them as text on an LCD screen.
Feel free to get involved and test this out or even help to improve it.

Built on an Arduino Mega 2560 with a 2x16 standard kit LCD.
Schematic now included in pdf. Incorrect naming of diagnostic socket pin FEN shown as FEM in schematic

Noteworthy files

MX5_Arduino_Diagnostic.ino

Contains the basic program functions.

• void setup() - sets up pins, lcd and attaches interrupt
• void loop() - main program loop
• void LogCode() - logs an error code when found into fault_array
• void FlashPin_Interrupt() - called when pin 21 changes state
• void NewFlashState() - decides what new state means i.e long flash, short flash etc
• void RebuildFaultArray() - rebuilds fault_array
• void UpdateDisplay() - updates the LCD display. Called from loop()

lcd_pages.ino

Sets up all of the different display pages of the LCD display.

• void LCD_ProductInfo() - shows the product information
• void LCD_ScanningCodes() - displays a visually pleasing scanning codes page so user has feedback to see scanner is doing something
• void LCD_NoCodesFound() - best result for user as displays no fault codes found in vehicle
• void LCD_CodesFound() - page that is displayed when fault codes are present
• Contains other functions used by the 4 noted above

Schematic PDF.pdf

Incorrect naming of diagnostic socket pin FEN shown as FEM in schematic
Circuit schematic to make the hardware the same as I have using an Arduino Mega 2560 and the 1602A LCD screen.
Pins B+, GND, TEN and FEN used from the Mazda MX5 under bonnet diagnostic socket.

Diagnostic socket possible pin meanings

• B+ : battery positive
• GND : battery negative
• TEN : test engine - drops engine into test mode for setting idle speed, ignition timing etc and prepares ecu for fault code output
• FEN : fault engine - reads out the fault codes via a sequence of going low Potentiometer is included to fine tune the contrast of the LCD screen, but once a nice resistance value is found that gives the best contrast for chosen LCD display, R1 could be swapped out for a resistor of that value.