It’s a two pronged attack

My board was designed for OSHpark’s 6/6 mil process, however APcircuit is a 7/7 mil process. I’ve asked them to go ahead, but it voids any guarantee of functionality so I’ll have to check the boards. As a result I also uploaded it to OSHpark and chose the “free” shipping option. It’ll cost 16 dollars for 6 boards as a backup, so I’d gladly get that underway now rather than in a week if the APC boards fail.

Accuity V4.1

And so it begins. Again.

I’m going to submit it to APcircuits in Alberta today or tomorrow. Problem is the drill holes are too small. Question is do I spend hours adjusting them or can they just drill them slightly bigger, but then they might over drill and cause disconnects. You can see the ST Micro Balun removed, replaced by discreet components with a trace antenna stolen directly from the EK and DK boards. I asked in an antenna group why all trace antennas are smaller than the 2.8mm calculated width for 50 ohm. I’ve yet to get a reply.

When I order the extra parts for these boards from Digikey I’ll probably get a few more St micro Baluns to try one more time. I think I have a better process, but I’m fairly certain something is messed up. Still not 100% sure it’s not the LFCLK, but pretty close.

Don’t copy– Okay, don’t mind if I do?

Nordic says don’t copy or use the EK and DK schematics as a reference . They say use the specific reference schematics and layout but design the antenna yourself. I don’t like that their Balun’s are different on the reference. I might ask why.
Sorry guys, but advice not taken. I’ve seen these work, with good range. The DK and EK trace antennas look to be identically built on 1.6mm FR4 boards with the same copper weight. The DK is two layer, the EK is four layer, but the antennas and components are identical. So I’ll try it.
ST Micro offered some help because of my twitter comment. After describing my problems they (correctly) blamed my reflow setup / stencil. I didn’t suspect it was a problem with their hardware, I suspect their Balun was meant for more professional production and that everyone, even the pros, will have to waste a few of these Baluns. Just less than me.  I just bit off too many things in one step. Namely trying to make an antenna setup while trying to get the ADS1248 onboard too and figuring out how to reflow a QFN. Baby steps people!
I might be able to shrink the size of the board back as the discreet balun moves the antenna up. This is good news as an L shaped board added 4mm to one dimension. This brings it back to near SD card sized I hope. 2 boards = 30 dollars, 4 = 50 dollars, and 30 dollars shipping. APcircuits turn around is hugely fast, so that’s who I’ll be going with on this. I’ll use OSHpark when I sort out any problems.

Did I kill my board?

After getting the last of the balun’s soldered I still can’t get it to transmit. It’s getting stuck at sd_softdevice_enable. I’ve tried everything. No luck. It indicates either:

1. The 32.768 khz crystal is not hooked (cold solder joint)
2. The transceiver is fried

I’m inclined to think the later because I can see a good solder joint, it even wraps around the edge a bit and there is clear separation between the pins. I suspect it’s a fried transceiver because I’ve had to reflow the board so many times and I think I’ve shorted ANT1 and ANT2 to each other, to ground, to Vcc, to just about everything. I have no Balun’s left. I did however receive 10 new nRF51422 from Mouser which I suspect I’ll be getting a tariff bill in the mail from Fedex. I mean, Fedex are jerks for cross boarder tariffs but they still be UPS by a wide margin.

Which of the following do I do?

• Design new board, order from APcircuits (1 week turn around at most). 6 boards = 100 dollars
• Design new board, order from OSHpark (25 day to 1 month turn around). 6 boards = 50 dollars (costs more to ship than the actual boards).
• Order new Baluns, build up last two boards. Might destroy these too but could be more careful?

It’s a hard decision. All involve even more money. I was asked today how much I’ve put into this project, and I really don’t want to think about it. I feel desperate to get this board working though. A month setback really starts pushing beta testing into next year as the ride season comes to a close.

Continually jumping off cliffs…

A friend of mine tweeted today:
“We have to continually be jumping off cliffs and developing our wings on the way down.” - Kurt Vonnegut
Since Friday (July 5th) I’ve jumped off of a lot of cliffs. About 9/10 times my “wings” didn’t work, leaving me to ask why. Okay, enough with the metaphors. On to ramblings about solder reflow and where my prototype boards are.

Delays on Post :(

I’m trying to reflow my circuit boards I recieved. Test 1 failed, test 2 in the oven cooling after a two stage reflow attempt. More details to come, but suffice to say QFN packages suck for DIY. I always suspected this would be an issue. Lots of test reflows went great, it’s just the stencil doesn’t work for the QFN (or BGA of the Balun). As a result I’m delaying my post entitled “Launching a Product” which will outline the next stages.

PCBs Arrive! Also, what is a Beta test?

The PCB’s arrived today. Six of them! So I have five I can ruin. I generally have good luck with PCB’s but I suspect this time I will not be so fortunate. I’ll mess up a few reflows before I get the IC’s soldered. Basically my first attempt will be just the Balun, nRF51422, and the crystals. I can sort the rest by soldering iron. It’ll be a lot of work, but I don’t want to ruin so many parts unnecessarily.

Here is something that has blown my mind. I’m basically still on track. I’ve got about 2 weeks to assemble and tune the PCB trace antenna and finish the enclosure design. . I am actually getting better estimating timelines it seems.

Really this is going to spill over to the build 5 – 10. Why? Well it’s simple -- I don’t have the strain gauges. I have three for the left sensor, but zero for the right (and I need 2 strain gauge rossettes for the right arm). I have lots of test beams to work with though, so continuing development won’t be a problem.

So here is a picture of where it will sit on the arm.

And now with chain rings.

There was a comment in my previous post asking what is my goal of all this. I’m going to explain this in a few days. The question asks “as I have alluded, I am a little confused as to where you are going with your economic and sales model." While I did a basic explanation, I think it’s time to spend some time presenting my long term goals with this – including major commitment points (including financial commitments), and potential exits (and reasons why I would exit). I’m going to spend the next few days pulling this together, so keep tuned. I’m aiming at Thursday or Friday post.

Beta Tests

I understand that I’ve confused several followers on several points. Some people who emailed me about beta involvement have offered money, or hardware. I can’t stress enough that I am not accepting money or hardware for the beta. I will be loaning the hardware to beta testers and will eventually reclaim it.

To clarify first off. An alpha test is where it’s been debugged by the developers and any other people who have been directly involved with the product development. A Beta test involves people who have generally considered an end user, they may be tech savvy or early adopters, who test and are willing to accept, work around, and report bugs and issues. They work with the developer to be fix problems and ensure the product is what consumers expect.

I still have to alpha test the V4 once it’s built. This should get it ready for beta, however the beta units will have to be built up so this will take a few weeks. I’ve compiled a list of people, their bike hardware, etc and I will be working to get things ready for them in the coming months.

The circuit board and strain gauges will be enclosed and able to deal with some light weather, but no major testing (such as IPX67) will have been conducted. The people who are local can have their units installed by myself, or a local bike shop if they prefer. Any non-local beta testers will have the crank shipped to them in original SRAM (or FSA potentially for BB30 / 386) packaging. Duration or testing is expected to be about about a month. Once the test is over I’ll pay for return shipping or for local testers I’ll replace the users original cranks. I’m mainly looking for verbal feedback, but files recorded via head units could be emailed to me which will aid in my development. I’ll be following up throughout the entire test. Probably weekly at pre determined times or via email.

Simple, right?