The world of automotive diagnostics has become increasingly accessible, thanks in part to affordable tools like Bluetooth OBD2 adapters. Recently, curiosity led to the disassembly of one such inexpensive device, purchased online for around £10 some time ago. The aim was simple: to understand what makes these budget-friendly tools tick, and to examine the components within what is essentially an 18 Pin Dip Obd2 Pcb Adapter in function, if not exact component configuration.
These compact devices often carry the “ELM327” label, referencing the ELM Electronics microcontroller renowned for translating vehicle onboard diagnostic (OBD) interface messages. According to industry resources, the ELM327 is built around a Microchip PIC18F2480 microcontroller. Modern vehicles utilize various OBD protocols, ranging from older standards like ISO 9141-2, ISO 14230-4 KWP, and J1850 (PWM, VPWM) to the more contemporary Controller Area Network (CAN) protocol. The ELM327 chip is designed to support all of these.
Further investigation reveals a crucial aspect of the ubiquitous cheap OBD2 adapters: cloning. Due to a lack of code protection on original ELM327 chips, unauthorized copies emerged. These clones, often from Chinese manufacturers and readily available on platforms like eBay, utilize firmware that falsely reports newer versions than the genuine article, despite offering similar core functionality. Many of these adapters misleadingly claim to be version 1.5, a version that is not officially recognized by ELM Electronics.
Close up view of the OBD2 adapter PCB after case removal showing electronic components
Upon opening the cheap OBD2 adapter, the internal Printed Circuit Board (PCB) reveals a surprisingly well-constructed layout. The OBD connector, linked to the PCB header via a 16-pin ribbon cable, was detached for closer inspection. The soldering quality appears satisfactory, and all components seem correctly placed. As anticipated, the primary microcontroller is indeed a PIC18F2480, mirroring the chip used in authentic ELM327 devices. However, the absence of official labeling strongly suggests this PIC18F2480 is loaded with cloned firmware, a common practice in these budget devices.
Comparing the PCB design to the example circuit diagrams found in the ELM327 datasheet, a clear resemblance emerges. The design appears to be a modified adaptation of the reference circuit. A notable addition is an off-the-shelf Bluetooth module (located in the middle right of the PCB). Furthermore, the RS232 level shifting circuitry has been omitted; the PIC microcontroller’s TX & RX lines connect directly to the Bluetooth module pins. A component-level examination reveals the presence of key elements beyond the main microcontroller. These include the MCP2551 CAN transceiver, a 78M05 5V regulator (bottom right, substituting a 78L05 from the schematic), a 1.5A 50V rectifier diode for reverse polarity protection, and an LM317 adjustable regulator for managing the J1850 bus voltage. Additional filtering components are also visible on the board.
Screenshot of ELM327 datasheet circuit diagram example
The Bluetooth module identified resembles the e-Gizmo EGBT-046S, often sold on eBay as HC-05 or HC-06 modules. The primary difference lies in the HC-05’s master/slave configuration capability, while the HC-06 is typically limited to slave mode. These modules are based on the CSR BC417143 BlueCore® 4-External single-chip radio and baseband IC, accompanied by an 8Mbit external flash memory chip containing the module’s firmware.
Powering up the OBD2 adapter PCB and establishing a Bluetooth connection with a PC allowed for communication via puTTY. Using the ELM327 AT command set, various commands could be tested. While vehicle-specific diagnostic commands were not applicable without a car connection, basic AT commands for device reset and firmware version reporting were functional.
Sending the “ATZ” command to reset the device resulted in a response of “ELM327 v1.4”. The command “AT@1” correctly returned “OBD2 to RS232 Interpreter,” indicating basic ELM327 functionality. However, the “AT@2” command, designed to display the device identifier in firmware versions 1.2 and later, yielded no response. This lack of response reinforces the conclusion that this particular OBD2 adapter is indeed a cloned version, as expected.
Despite its cloned nature, the cost-effectiveness is undeniable. Original ELM327 ICs from ELM Electronics are priced at $18 for the chip alone. Factoring in the CAN transceiver, additional components, PCB fabrication, and enclosure costs, replicating this device from scratch would significantly exceed the initial £10 purchase price. Ultimately, even as a clone, the adapter delivers functional OBD2 communication capabilities at a remarkably low price point, making basic automotive diagnostics accessible to a wider audience.
