Building the ELM329 CAN Device - Part III

So After the first build had failed I determined that the problem was with the CP2102 USB Chip. If I looked closely I could see a solder bridge under one side. It'll take some time to fix it (if it's even possible at this time), so instead I decided to kick off another batch of boards as practice.

As I mentioned earlier I have 3 different revisions of the boards, the red 1.1, a purple 1.2 and purple 1.3. I figured I would try to make one of each for a comparison - between them the layout has a few slight changes and a few component differences. After going through the usual process of the stencil, paste, placement etc I baked all 3 PCBs at the same time.

After a nice baking session

I'm not sure if you can tell, but the center IC on the Red board (almost looks orange in the picture!) actually had couple of solder bridges, so I set that one aside so I could use some solderwick on it later. Also, while the backs are 99% the same between the different version, I noticed I had moved quite a few things around on the 1.2/1.3 revision, so the top stencil simply would not work with the 1.1 board. So it looks like they are either a) Coasters b) in need of a separate stencil, or c) I'll be doing a partial stencil job and do the rest by hand in the near future.

When I went to check the other 2 board, they both seemed fine. I did notice in testing though that for the USB to be seen on my computer I had to apply 12V to the circuit as well (used an old router power supply). That surely is a bit of an inconvenience for further testing, however when doing that my computer was successfully able to open the port and talk to the ELM329 chips.

Next we getting the PCB all connected and built into the housing. I re-used the housing from an existing ELM327 instead of a new one, since that already had some wires connected to the OBD connecter and had a 8 pin plug. After taking off any of the wires we didn't need, soldering a new one to pin 1 for SWCan, and moving the wires to their right spot in the 8pin connector it was ready to go in. I had meanwhile also made a usb cable to connect to the 4 pin connector on the PCB.
The final result looked pretty sharp!

Everything all connected

Yes the RED wire is Ground.... Crazy Chinese people... I didn't bother to change it

Ready to use! Now if only I had a snazzy sticker...

The device defaults to Hi-Speed CAN, and thereby lets you use whatever ELM327 Software you may have that supports CAN commands. A Quick test showed this to work, and when switching over to the SWCan chip, by issuing an 'AT C1' command, we were able to also see data using a terminal app, so it looked like a success!

Next, I will try to build a few more boards , but also perhaps write some software for it to easily interface with it since right now it's really more an 'advanced users only' tool.

Building the ELM329 CAN Device - Part II

So I finally had (made) some time to finish the front side of the first ELM329 pcb. The process is basically identical to the back-side where I used a stencil to apply solder paste, then place the components (obviously making sure the polarity is correct for diodes/LEDs etc), and toss it into the toaster oven. This side was a little more work actually since it had a few more components, and it had some 'odd' components such as the USB Chip that has all the pins connected underneath etc.

Paste Applied and Components Placed

When it was time to put the pcb in the toaster oven I took two pieces of aluminum foil and roll them up to make little 'offsets' to place the board on. This way the rack wouldn't be touching the components that were on the bottom side and possibly disturb them.

Sitting on it's 'fancy' mount

The problem components were the 2 aluminum caps which you can see in the above picture being closest to the front. They were not very stable and one even fell off in the oven! While they may be a LOT cheaper than the Tantalum caps, I'm tempted to switch back to those since they don't seem to be that wobbly. You can even tell in the picture that they are leaning.

The baking seemed to take longer than last time, but keeping a keen eye on it, eventually the solder paste started to reflow. The voltage regulator took the longest, probably because it has a large heatsink area. At first glance everything seemed OK, But i'll have to take closer look with a magnifier to make sure everything flowed the way it was supposed to. Of course as soon as I turned off the oven and opened the door a little whisp of smoke came from 'somewhere' so who knows what I fried...

Fresh out of the oven - Hmmm tasty!

After letting it cool down I manually soldered the header pins in place (1x for OBD and 1x for USB). Now I just need to finish up the USB cable so I can test it out and see if I screwed up anything beyond repair. Also the bottom-side components stayed neatly in place so with some tweaking this method of making PCBs is definitely viable.

Lastly here are a few more pictures of the unique soldermask color.. depending on the light it looks either purple or blue-ish (mostly purple though)

It's Purple!

No it's Blue!

Building the ELM329 CAN Device - Part I

After a lot of digging I had finally found a supplier for the device enclosure that offered the exact enclosure I had based my design on. They were (of course) in China, but I decided to just go for it, since after doing some research they did appear like an official business. I had placed my order on a Thursday evening, and I had not heard anything by that Monday so I contacted them to see what the status was, fully expecting it would take another week or so before they'd even ship the product etc. To my surprise they did not only provide me with a valid tracking number right away, when checking the number on UPS it showed the package was already in California and making it's way up here so I would receive them the next day! Consider me impressed!

Device Enclosure with USB Cable

Meanwhile I also ordered a handful of the ELM329 chips from ElmElectronics.com. At $21 a piece they're not cheap, but hopefully I can recoup some of the cost by selling a few devices after I've confirmed this design actually works OK etc. (For those of you leaving comments interested in the Eagle files etc - I haven't decided yet if I will - or when, but I may simply sell some ready-built devices on GRRRR8.net or Ebay)

Now it was time to start building the PCBs - I basically watched a bunch of tutorials and figured - how hard can it be? so I dove straight in. First I started with the bottom side of the board. Since I have 2 layer PCB with both the Top AND Bottom populated, I'll have to bake the board twice - once per each side. Based on this I figured I'd do the side with the smallest / lightest components first so that once it comes time for the 2nd bake I wouldn't have the large chip etc hanging upside down and possible re-flowing to the point of falling off. Supposedly the surface tension will hold on any of these components just fine, so that will be an interesting 2nd session.

Usually you want to put your board somewhere solid (desk/workbench/counter) and in a frame so that it doesn't move. Because I didn't bother making a custom frame I used the common trick of making two L-Shapes out of extra PCBs and taping those down to the work area. They are the same thickness so there are no weird bumps when it's time to apply the paste. Next I put a piece of tape on my bottom-side OharaRP Kaplan Stencil and secured it so that it lined up just right, and I could still lift it up on one side.

Frame out of Extra PCBs & Stencilon top of PCB - Ready for the paste!

I had purchased a small jar of Lead-Free solder paste which was thicker than I thought it would be. It roughly had the consistency of grout you use with ceramic tiles etc while I was expecting it to be runnier for some reason (perhaps I had seen too many videos of people using the syringe paste..). Now normally you need some kind of tool to spread the paste on - Some places sell a $50+ specialty solder paste applicator, while others use a $5 homedepot spackle/putty knife. I went super cheap and used an old plastic card much like a credit card. This actually worked beautifully: I scooped some paste out of the jar and basically smeared it over the area. Then I ran the edge of my 'tool'  at a shallow horizontal angle to work the paste into the openings in the stencil. A second run over it, but this time more vertical cleaned 98% of the paste right off the stencil and left the pads nicely coated and I simply scraped the excess back into the little jar.

Paste applied through the stencil

Stencil lifted away showing the gray solder paste on the pads

After this it was time to place the components. For my SWCan ELM327 I had used 1206 components which took some getting used to. This time we were down to 0805 size components - If I had to hand-solder this stuff I would probably stick with 1206, but since all I really had to do was place them on the board for the reflow they weren't that bad to work with at all. I did notice that I probably should've made my silkscreen font a LITTLE bit bigger because at times it was hard to tell what the component was supposed to be.. (Is it R8 or R9??). After some work with the tweezers I ended up with this:

All components placed and ready for baking

Next step was to actually bake the board. I had gotten a small 1000W toaster oven (cheapest I could find) that went up to 450 degrees Fahrenheit. I didn't bother with getting a special controller for reflow profiles etc since these things take a while to heat up anyway. So, Instead I went at it barebones like many others have done. Basically pop in the board, turn on the oven to 400-450 and simply wait for solder to reflow, wait a few seconds, then turn it off and pop open the door to let it cool off.

Baking away

Cookies are done!

The end result looked really good - I would never guess this was done by some amateur in their kitchen vs a professional PCB house. Now the wait is on for the mail to deliver the ELM329 chips so I can try the other side and hopefully not screw up :)

ELM329 PCBS have arrived

Not really of interest to most people, but I'm excited about it so I figured I'd post about it. As I mentioned in a previous post, I had been goofing off in Eagle and sketched up a PCB for the ELM329 chip and the end result looking somewhat like this:

It would be a direct replacement PCB for the Generic ELM327 Clone boxes you find on ebay as shown in another previous post.

I had sent out for a batch of 10 PCBs and chose a Red Soldermask instead of the Blue depicted. Then, as I was waiting for these and being the eternal tinkerer, I kept playing with the schematic & layout and made another revision. It was a small change, but I wanted to get that board made too, so I send out to have 3 made through DorkBotPCB, which usually gives you a snazzy Dark-Purple with gold pads PCB. After I got that order in, I found that the Tantalum caps I was using (and were a few bucks EACH) could easily be replaced with an aluminum can cap that only costs 53 cents.. so Revision 1.3 followed soon after - and once again I ordered 3 boards of that revision. Of course incredible timing follows that I would receive all boards all at the same time!

All boards lined up - That's some groovy purple!

As you can see I have the 10 red revision 1.0 boards in the back,
then 3 revision 1.2 boards (yes I had an intermediate revision 1.1 I never had made), and in front the 3 latest revision 1.3 boards

I also ordered a Kapton SMD Stencil from OharaRP so I can try to bake these boards in a toaster oven instead of trying to hand solder all this tiny stuff.

The Silkscreen layer on all them is not the best since I did not really worry about Vias etc breaking up text (which it does XD ), since I would be doing the assembly most likely, but perhaps if I get to a revision 1.4 I'll tweak that a little bit too.

Original ELM327 Clone with the new PCB next to it

What's interesting is that this is the second clone I have of the generic ELM327s and the board is actually a bit different component wise than the first ( that one still has the SWCan mod in it).
Also if you have a keen eye you will spot something off.. The connecter for the USB on my board is actually smaller! Guess I'll have to redo the USB-Cables as well.. Apparently I used a standard 1.5mm pitch 4 pin connector, while the original board had a .1"/2.54mm pitch connector. Always something that goes wrong ;) At least it fits in the enclosure just right!

Fits just right!

Of course I have been looking at the new STN1170 chip which is looking pretty nice as well ( and cheaper than the ELM329) so perhaps a new batch will be a brand new design based on that chip instead. Meanwhile I have the actual board parts such as resistors, capacitors etc etc arriving tomorrow, so then I just need to get my hands on a toaster oven, and some time , which is usually the problem....