Teardown: OBD-II Bluetooth adapter

August 27, 2013 // By Michael Dunn
I'm not into cars to such an extent that I have an OBD-II (On-Board Diagnostics – 2) analyser in my toolkit. But when I discovered Chinese sources for $9-$20, USB and Bluetooth adapters, I couldn't say no.

Actually, my search for OBD capability was inspired by a persistent check-engine idiot light (spoiler: it was only a cylinder misfire – something I could have already told you before the light ever came on!). I found that the usual Chinese sources carried many wired and wireless adapters, and I ended up getting this one from the wonderfully named Banggood site. I knew it might not work, but it had good reviews, and I wasn't risking much.

Sure enough, it did work – well enough at least to report the misfire code and let me turn off the engine light. Then, curiosity got the better of me, and I had to see what was inside. I'll leave it to an enterprising reader to figure out the BOM cost. How can they make it so cheaply?

The picture above is the dongle – it doesn't know what's about to hit it. The LEDs do activate when the device is in use, but it's not clear if they have specific meanings. LED-less dongles of about 1/3 the size are also available. I thought it might have one of those easy-to-snap-together, hard-to-unsnap cases, but no, I found the screws.

A look at the guts – the overall quality is surprisingly high:

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