I'd ordered a couple of ELM327 compatible adapters from Aliexpress expecting that these would be similar to the item in the image below. Normally these contain a PCB board to fit the enclosure and populated with the unknown MCU (covered with epoxy), a Bluetooth chip, CAN transceiver and the necessary circuity to support a K-Line interface.
After dissecting the received adapters here is what we have, 80% air and a small pcb.
Pictures of the small PCB reveal a single 16 SOP package (and a 24Mhz crystal) with the chip marking etched out and no BLE chip or CAN transceiver present 😒. Is this one chip doing all the work?
From a software point of view the device reports itself as ELM V2.1 and I managed to retrieve the firmware version as TDA99 V0.34.0628C (not sure what it means though). The firmware is extremely buggy and feature wise incomplete for ELM V2.1.
The intriguing question was "could a 16 pin chip" replace a number of discrete components. After days of research it turns out the chip seems to be a repurposed Bluetooth audio/toy chip (possibly from ZhuHai Jieli Technology ). The same unmarked chip seems to be present on the Thinmi ELM327C with the chip referred to as QBD255. Can't locate any information for the QBD255. Worst to come is that the CAN implementation seems to be completely written in software (hence no CAN transceiver) and therefore prone to timing errors and limited data rates. Furthermore this chip must have limited memory/flash hence the incomplete implementation of ELM features.
I suspect this chip may be the Jieli AC6329F or AC6329C but need to prove it somehow?
There seems to be another chipset floating around from YMIOT, described as "ELM327 V2.1 Bluetooth universal diagnostic adapter with 16-pin YM1130 1343E38 chip"
History of this chipset is below:
2017 - YM1120 (131G76)
2018 - YM1122 (1218F57) & YM1121
2019 - YM1130 (1343E38)