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Prying eyes: Low-cost OBD-II Bluetooth adapter

03 Sep 2013  | Michael Dunn

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Looking at what I'll call the underside of the board reveals a Microchip MCP2551 CAN transceiver, a 4MHz crystal, an Advanced Monolithic Systems AMS1117 3.3V LDO in the upper-left (ever heard of them? I assume this is the same as an LT1117), five LEDs along the top, and a 78M05 5V regulator at the lower-left. The two diodes to the right of the regulator made me think of varactors for some reason, but a code lookup shows they are probably 6.8V Zeners.

The quality of soldering and general manufacture is excellent. The only flux residue on this side of the board is from a 3-lead through-hole component, which brings us to the topside.

Now things get interesting, though let's start with the mundane. The through-hole TO-92 is a good old LM317 regulator. The two connectors did not "flow" into alignment very well, even though they have their "ears" soldered to the board. I'll guess that the unpopulated chip is for a serial-to-USB converter for a wired version of the board. The big chip is a PIC18F25K80—not too shabby a part, with 32K flash, 3.5K RAM, 1K data EEPROM, CAN, 12bit ADC, 16MIPS, etc. It alone is worth about $2 in decent quantity!

That leaves the very badly soldered Bluetooth module, blue soldermask and all. The top three contacts on the left edge aren't even soldered! Are they supposed to be? I could compare it to the original unit I bought (I haven't actually tried this one).

The chips on the Bluetooth module comprise an FM24C64, which I assumed was just a common 64Kb EEPROM, but actually appears to be a more exotic FRAM! That's the first FRAM I've seen in the wild. The chip to the right of the FRAM has me stumped. Let us know if you can figure it out. But the IC at the lower-right is an RDA Microelectronics RDA5869 Bluetooth SoC, a 55nm design with an ARM7µC.

Many of the components have this year's date code, so production is current. I get the impression the firmware in these cheap units might actually be...ahem...borrowed from an original design, and I don't know how well it works with the range of car models and years sporting OBD-II, but it did what I needed for my 1998 Toyota.

About the author
Michael Dunn is an editor for EDN.

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