mbed

Hi Andrew,

Great feedback. I updated the design to v0.03 - incorporating your feedback as best I could. I didn't go with the DIP switches because they take a lot of space (increases PCB cost), and in an industrialized use they are not generally as reliable as I would like. You'll also see that a few of the jumpers can now be cross-point wired, which would have taken more DIP switches. And of course, bare wire can be used to permanently set an implementation.

I haven't yet done much of a "power" study - what can the mbed source to the USB, or if the single TO-220 regulator, without much of a heatsink, can support much in the way of loads.

Please look this over and let me know what you think.

Hi David,

I can't see your v0.03 schematic or PCB. The links seem to be broken, for me at least

Fixed - sorry about that. I'm not sure if it is the wiki software or me. I think when I upload the documents it converts spaces to underscores, but when I create the links, it doesn't. I was racing a bit too fast this morning.

What program are you using to make the 3D rendering?

Lerche

Hi Lerche,

The Schematic and PCB are designed with Eagle. It was then rendered in Eagle3D (not from Cadsoft), which I came across just a few days ago. Perhaps interestingly, while seeking out a faster way to make new parts, I came across EagleUp, which I haven't yet tried. And just seconds ago - while searching for the EagleUp URL, I came across this hybrid of the two. These technologies are sufficiently cool that I had to remind myself of my original objective - so I refrained from starting a 3D project to create the mbed component.

Common to both is an integration to Eagle with the ULP (User Language Programs) that can basically read your PCB information and translate that into something compatible with the external rendering tools.

I just updated with version 0.04 design. Some part changes allowed me to reduce the PCB size a little bit, which saves space and money. I was trying to find a way to get power over the ethernet cable, but that wasn't possible with the available connector that has RJ45 and USB-A. My current goal is to send this design out for PCB manufacture about mid-December 2010.

David, you could easily add non-IEEE-compliant PoE if you only need it to work on your own, controlled networks. Just use the two spare pairs as positive and negative, and perhaps add a SimpleSwitcher or similar to your board (you really ought to be using high-ish DC voltages (perhaps 18, 24 or 36 V) otherwise the copper losses are atrocious. With such high DC voltages, a linear regulator or LDO is going to get *very* hot running an mbed).

For example, these pre-assembled adapters use 4/5 for DC+ and 7/8 for DC-.

http://www.solwise.co.uk/wireless-poe-injector-diy.htm

SimpleSwitcher:

http://www.sparkfun.com/commerce/product_info.php?products_id=9654

Hugo, thanks for the quick feedback. I was looking for an RJ45 that would let me tap in - similar to what I have on an old Ethernut board. But this connector is a combo RJ45 and USB, and in my search to date, I couldn't find one that grants me access to the "ether-side". If you happen to know of a part, that might be the reason for v0.05. The SimpleSwitcher looks like quite a nice part - few external parts. As the rest of the BOM is about $30 and that adds $19, I'll have to do a bit more research on that part - perhaps see how much board space is required.

Oh I see, you can't do that because you're using a connector with integrated magnetics. Your best bet is probably a plain, passive connector and separate magnetics (it'll be cheaper too, but will take up more space).

Regarding the SimpleSwitcher, other devices in that series go down to around $11 in one-off quantity, but a discrete DC/DC would be a lot cheaper - I like the SimpleSwitchers for their extreme simplicity and integration, and because you don't need to find a suitable inductor (which can be tricky). Another simple, cheap but larger solution might be something like Digikey 811-2196-5-ND or similar (there are many thousands of DC/DC modules on Digikey...).

Hello David,

really nice board.

I think you will need a large CAP ( at least 100 uf) at the regulated 3V3 supply side because if you connect, for example a MAXStream zigbee module, strange things can happen during transmitting. You power everything via mbeds 3V3 regulator and a larger CAP can support the Voltage regulator when a lot of current is needed for a very short periode.

best regards

Franz

Hugo Vincent wrote:

... Another simple, cheap but larger solution might be something like Digikey 811-2196-5-ND or similar (there are many thousands of DC/DC modules on Digikey...).

That part looks quite interesting, and if I check the footprint, it appears to be a simple bom substitution. Thanks.

Franz Achatz wrote:

I think you will need a large CAP ( at least 100 uf) at the regulated 3V3 supply side ...

I'll see if I can fit in this cap. From the mbed schematic, it appears the 3V3 is only for external circuitry. I didn't see it go anywhere but to the external pin.

Hi David,

you have GND on top and bottom side, right, using a GND-polygon? Maybe its an idea placing some more extra vias (name the vias to "GND") to get better GND connections between the two layers. This saves a lot of gnd-routing-work, too :-) See my attached example:

Franz - Thanks - I'll incorporate the extra ground vias before I go to manufacture.

Baseboard v0.05 posted - Schematic, PCB, 3-D representation, BOM, and design notes. I also released files for PCB manufacture and ordered parts. The next phase of fun will start soon.

David,

What are your plans for the finished design?  I own a LPKF board plotter and would like to build somthing like this for personal use.  If you are interested in selling a non-commercial license for the Eagle layout I'd be interested in buying one.

I'm interested in 4 immediately

I ordered 2 from batch-pcb and today, four arrived. Very nice quality for such a low price.

This is the first time I have used the service, so if anyone knows why I got extra boards please let me know.

Thanks!

I get the impression that receiving double orders from batch-pcb is not uncommon - the same happened with my original order from there.

Great board! Exactly what I need for my project. I need to communicate to 2 different canbus devices and then talk bluetooth to an android device.

Got the parts ordered, but there were a couple BOM issues I noticed:

• ADM3202ANZ, IC TXRX DUAL RS232 3.3V 16DIP, I only found one on the board, there are 2 on the BOM
• 3-644456-3, CONN HEADER VERT 3POS .100 TIN, I only found 12 on the board, there are 14 on the BOM
• SFH11-PBPC-D10-ST-BK, CONN HEADR FMALE 20POS .1" DL AU, I cannot locate this. I think this was meant to be a D20. The ones I got will not fit end to end and are unuseable for IC1.

Also, I figured I'll mention here, Batch PCB isn't a fast service, and can take up to 4 weeks while they wait to fill a panel. I didn't know this and after 10 days, started to wonder about my order and found more info in their FAQ. Just for those ordering, it's not going to come in the mail within a week.

Hi Travis, Great feedback on the BOM. Sorry about the errors in there. I updated the BOM linked above to a rev 'b' based on your notes.

And for Batch PCB, I agree on the speed of their delivery - I had one project's boards arrive in just over 2 weeks, but I think the 3 to 4 weeks is much more typical.

Great work on this board BTW David. Meets 90% of my needs (I only added an RN-42-SM http://www.rovingnetworks.com/products/RN_42_SM). Thanks for fixing the BOM.

WRT the boards, I got a note yesterday from BatchPCB saying the order shipped. Right at 2 weeks actually. Just making sure people knew that it might not be 2-3 days like we're used to for the parts.

Should be building this next week, will let you know how it goes.

C22 is missing from the BOM, it's a 10uF cap same as C2 and C3. Also, the - silkscreen on C2, C3 and C22 is under the pad, so you can't tell. The Square is positive for those putting it together.

Thanks again Travis. The library I used for those caps also had a rather subtle minus sign next to the round pad. As you know, some parts like to label the negative terminal and others the positive... I updated the BOM to rev c, and I'll also take note of the silkscreen issues, so some future PCB layout will fix those items.

Everything works so far, going to test Canbus this weekend (hopefully my OBD cable and serial LCD from sparkfun arrives). The SD card, USB, LED's and serial all work well.

In future updates, maybe keep the jumpers away from large parts. The jumpers near the ethernet/USB device are a bit hard to fit my fingers onto. I think you mentioned the clearance for the high power part already, but I just made the leads longer on the cap and kind-of bent it over.

It went together very easily though, and I always double checked via the PCB pdf to make sure I got the right locations and parts. Built 2 boards in one evening in 2hrs. Great documentation and the test code works great, thanks for putting it all together.

Got back to the Smartboard last week and started working with CANbus. I'm using a Bluetooth-OBD2 dongle to connect via bluetooth to the smartboard CANbus. Essentially I want to create a little ECU for use in my own projects (PID smoker, Electric motorcycle, etc). I use a program called Torque which is meant to run on an Android device and can display many different graphs, gauges, etc, as well as log other info like GPS, accelerometer data, timestamp.... which is fairly useful as a portable display. Got the Torque app to talk to the dongle and I'm seeing the OBD PID requests come through on CANbus, and I send them to the LCD (and pc serial port). So far so good. I've got two of the smartboards, one is in the middle, one is at the end, and the BT-OBD dongle is at the other end. This board makes it super simple to work with Canbus, TTL and RS232 serial, USB, SD and ethernet.

Just a couple things for the wishlist: - It would be really nice to have a jumper to select using the termination resistor or not. I know you can wire one into the terminals, but I've lost a couple 120ohm resistors... but never run out of jumpers. - I realize size is an issue, but I wouldn't mind a slightly bigger board that includes the silkscreen designations. Right now they're under the connectors, so I always find myself re-referencing the PCB layout and Schematic.

Thanks for the positive feedback Travis. And it sounds like you're putting the SmartBoard to work in some interesting ways.

With respect to your wishlist - I added your suggestions to my list. I actually tried to put in jumpers for the termination resistors, but couldn't find the space (and I didn't want to make the PCB bigger). So, I'll struggle with this request for sure. I also thought about leaving off some of the flexibility (the space for which could then be reclaimed for things like this), but here too, I've actually used nearly every circuit that I designed in for one project or experiment or another.

No worries, I'm an engineer, so I value feedback and I hope you do as well. It's the only way we make things better!

It's a great board IMHO, and I think it's one of the best ones out there as far as features go.

Is there a reason you had to make it as small as you did?

Neither the A_CANAdapter or A_SmartBoard_HWTester are working anymore... they have a bunch of compile errors. Looks like the latest update took them down.

Software update - sorry for the delay - other projects had priority. I just rebuilt A_CANAdapter and A_SmartBoard_HWTester and both are working now. I guess with the mbed library updating several times a few tweaks were in order. If you find any issues, please let me know.

No worries, I was just messing around with em and figured I'd let you know. Thanks for updating them. I'll test em out for you as soon as I can.

Hi David, will there be an option to purchase the fully populated version of this board, as in ready-to-use? The twin-CAN makes it of particular interest to me :)

Hi Jason,

Well, I hope I don't dissappoint you too much - I looked at a couple of options along this line, but haven't done anything yet. From basic component pricing, there is good price scaling by buying enough parts for 20 to 50 of these at a time, but I think that is really far short of what it would take to affordably engage a manufacturing house.

That's why I designed it with through-hole components as much as possible - so a hobbyist could successfully build it, and I would certainly encourage that! If you haven't done any soldering before, about $11 at a Radio Shack (or elsewhere online) would get you the tools to get started. Is there something like a Radio Shack in your part of the world? And for a bit more money you could buy a small kit or two to practice on. And there are lots of online soldering tutorials as well.