Custom Hi-Speed CAN/ SWCAN Scanner (ELM329)

So after modifying an existing ELM327 Clone I read about the new ELM329 chip - it is specifically targeted for CAN Networks and sounded like a very interesting option. When I did some more research on it I ran across a post over on MP3Car.com where 'reinoso' showed off a board he developed. The cool thing about it was that he added a switching mechanism to select between Hi-Speed CAN or Single-Wire Can.

I figured it would be a fun exercise to try to design something similar. The ELM329 Datasheet provides the basic reference schematic so it was just a matter to add the switching mechanism and draw up the new schematic and PCB. Initially I started out in Altium Designer (which is GREAT) because Eagle is just too... shall we say 'quirky' (though some call it 'female' because it's illogical lol). Being a software engineer by trade, it has too many 'WTF were they thinking' issues - yes you can get used to them, but the fact they're even there just bugs me ;) . However as I got a little deeper into it I figured that if I ever wanted to release the schematic/pcb etc for public use, not too many people have Altium Designer, and thus would not be able to use it. so begrudgingly I went back to Eagle.

My goal for right now was to at least get the schematic going properly and then for a first build have the PCB fit inside the generic ELM327 device box I already have. I measured it's PCB and based my layout on that so that it would be a drop-in replacement. I kept both connectors (USB (4-pin) & OBD (original 8-pin) ) in the same place to make it as seamless a swap as possible.

For the actual soldering process I wanted to try out the reflow toaster over method, so for the main passive components I felt fine going to 0805 component size (yes I've heard of people doing 06 or 04 etc without problems, but I'm not the steadiest hand). The ELM329 comes in a SOIC28 (or DIP package) which is relatively large. Also for the USB connectivity I went with the SiLabs CP2102 - it only needs a few extra components, but it's definitely not a hand solder component being a 28-VFQFN component.

Top View of PCB

Bottom View of Board showing Both Can Transceivers and switch IC

Another Angle of the Top

I Made the above 3d previews using the EagleUp Plugin for Sketchup.Not all components were available so I had to get creative in making some of them myself (e.g. the 4 pin header block) & the MSOP 10 package for the switch (IC2) on the bottom.

Now it's off to finding a decent PCB Manufacturer who can build a few of these boards for a decent price.

Of course it will be interesting to apply this to the upcoming STN1117 chip and minimize the footprint even more.