Open-source ELM327 OBD adapter


The AllPro adapter is a small device that plugs into your automobile's On-Board Diagnostic (OBD) port, which grants access to the car's computerized self diagnostic system. All cars manufactured in 1996 and later have an OBD-II port, which is usually located under the dashboard on the driver's side.The adapter allows you to interface with your car's OBD-II bus. It provides you a serial interface using the ELM327 command set and supports all OBD-II standards:

  • SAE J1850 PWM
  • SAE J1850 VPW
  • ISO 9141-2
  • ISO 14230-4
  • ISO 15765-4 CAN
  • SAE J1939




The adapter kit schematic is shown here. It is built around NXP LPC1517 Cortex-M3 microprocessor with 64 kB program memory, but can accommodate another chip from same family like LPC1549 with 256 kB if required. The NXP chips has a ROM-based bootloader that supports loading a binary image into its flash memory using USART or CAN. All the software is written in C++ for NXP LPCXpresso IDE which is essentially using GNU toolchain for ARM Cortex-M processors. However, it can be compiled with other pre-built GNU toolchain, like GCC ARM Embedded or even with Keil uVision IDE.


The Highlights

  • NXP LPC1517JDB48 ARM Cortex M3 72Mhz processor
  • 64kB Flash, 12kB RAM
  • Using NXP sophisticated State Configurable Timers to do the precise signal handling for J1850 PWM and VPW protocols
  • CAN FIFO buffers for handling some not-strict ISO-compliant ECUs
  • Botloader for initial firmware programming
  • Low power consumption

See building the adapter firmware from the source code. Or, if you just want to program the firmware check the programming the Adapter with Flash Magic. Also, you might consider ELM329 AllPro adapter. It is year 2018 and most likely you need only CAN protocol.



Adapter firmware:

The software and other materials in is released under GPLv3. If you want to reuse the source code in your commercial products, contact me for a commercial license.

The printed circuit board data are available separately:


The OBD-II Cable Connector

The adapter uses eight pin connector to link up to vehicle's OBD-II J1962.

J4 Description J1962 Pin
1 Signal Ground 5
2 CAN High 6
3 CAN Low 14
4 J1850 Bus + 2
5 Vehicle Battery Positive 16
7 K Line 7
8 J1850 Bus - 10



Bluetooth AllPro

Bluetooth version of AllPro adapter is ready-to-use fitted to "de-facto" standard OBD connector case and paired with SPC-CA v3.0 Bluetooth module based on Beken BK3231 chip.


Here is the popular Android Torque application output:



The USB version of AllPro adapter is using FT230XS USB to UART chip. Here is the schematic. The FTDI chip is crystal-less with the synchronization for this oscillator can be taken from the USB data stream itself and clocking Cortex processor as well. It also providing 3.3V from internal VREG.