Single Sided Measurement, Kickstater Coming to Canada

Just a reminder, the above board made by APCircuits has worked out well. They are a 7/7 mil service however the board was designed for 6/6 mil process of OSHpark. The problem was the turn around. APCircuits had the order on a Wednesday night and it was delivered Monday afternoon. Total cost is $88 dollars shipped with Fedex Priority which was $30 for 4 boards. OSHpark is 17 shipped for 6 boards.

APCircuits are very good, they reminded me that there were “errors” in the board, but as previously mentioned I told them to go ahead. I haven’t found a single problem with the boards and I’ve tested all the small traces. I have tested the RTD sensor lines but they are larger to decrease resistance so I’m not concerned.

Above is the board connected to the debugger, battery and a single full bridge setup which is connected to my 4 setup test arm used in thermal testing from here. This means it’s pretty much equivalent to the Stages One powermeter. Single sided, but that’s just for testing out, coding and debugging.

Below are a few more pictures.

I expect that I’m going to have to re-adjust timelines. I’m away beginning of next month for a wedding and waiting until I’m back to order the strain gauges needed. I’m going to look into re-adjusting my proposed schedule and see what I can do. The “to do” list is still extensive but nothing impossible. The hardest thing really was the reflow. While still not perfect it’s fine. Again, the solution was to ditch the BGA package. That’s advice for any hobbyist with a DIY reflow oven. BGA is too much of a headache, QFN is hard but not impossible. Still haven’t received any import bill for mouser yet.

1. Finish coding that couldn’t proceed until the boards were completed and working
• I only coded initially for one side
• I’m cheating and only outputting raw reads to the power, this is mainly for debugging
• Sort out UART connection to help “debug”
• Look at implementing TE/PS measurements – This is low priority as no head units can read it
• I won’t code thermal until later and I get a sample RTD from omega
2. Enclosure design – I decided to hold back a bit on this due to adjustments that might need to be made for the board design.
3. Instrument another crank (or V3 to conserve cranks, have to rework it by removing old gauges and installing the new ones in the right locations (slight movement and different gauges)) and connect up powermeter.
4. Mount battery, measure current consumption.

My rate of work on this has to slow down anyway from both a financial position and a time position. The board was the main hurdle at this point, right now getting it together. However I am seriously looking at Kickstarter when it comes to Canada in order to offer the Board (~$40), Dev units ($500 – 600), and final units on Hollow Forged Cranks ($700 FCC Approved). At least that’s the goal. I’ll know more when I get circuit board manufacturing quotes and find out minimum order quantities in a few weeks.

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.

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.

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?

Boards Shipped and Cost Analysis coming soon

Shipped! They were very quick at turning around the depanelizing of the other 92 orders and getting these in the post.

Obviously nothing huge in terms of news until I get these and try to reflow but I’m still here.

In other news DCrainmaker has an update on the stages powermeter. It seems they’ve dialled it in a bit. Honestly, while I think it’s as good in terms of accuracy it seems it’s holding up very well to scrutiny by several seasoned riders of the meter. For two stain gauge pairs and what I’ve proven to be 30 dollars of circuit boards on what I estimate to be a 30 dollar crank arm (I’ve sourced SRAM Rival’s for approximately $100 CAD + shipping) so these are 600 dollars for R&D / lights on / profit. In my world profit is really just R&D money.

This leads me to make comment on what I’ve seen in the industry in terms of pricing. While powermeters are getting more popular, all one has to do is spend 10 minutes searching craigslist / kijiji / etc to find that locally they are rare. So rare that I’ve seen someone in Alberta want 1500 for the SPIDER from a Quarq S975. Locally in Ontario it’s only recently that I’ve seen up to 4 Quarq units available and 2 - 3 SRM.

While looking for a test unit I spent some time and eventually got one reasonably priced which I plan on selling come Sept. These aren’t high volume products currently. This leads me to potential pricing structures, motivated by a person who emailed me asking me straight out “why do I [you] think power meters are so expensive”. I paused, and it felt like an epiphany. It’s not the parts, it’s the people!

I plan on posting soon about what it really costs, based on what I’ve learned today, to build and Sell a powermeter, and not take a loss. It’s harder than one thinks and I’m sure not everyone who were successful on being funded on Kickstarter or Indigogo have thought on this. I’ve read about a few who had no idea how to scale production from tens to hundreds, and were bunt (sometimes repeatedly) on the way. This has been the reason why you aren’t allowed to just show a 3D rendering of a product anymore for Kickstarter. Too many people who haven’t deliver or were months to over a year away.

Stay tuned and look forward to my post this week going to be called, “Good, Cheap, and Fast – Pick two”

Boards Ordered

Firstly I want to give a huge thanks to Paul Archer. In my day job my employer has signs everywhere that say “Verify your design inputs”, and to that end we have a process of independent verification for everything. Paul has been that sounding board and verifier in the last couple of weeks, and without him I could have spent a lot more time dealing with issues of this board. I won’t say it’s perfect but it should work well.

I’m using a Texas instruments reference design for an PIFA style antenna that’s been extended. I plan to tune it with a 2.4GHz spectrum analyser by measuring power output. I’ve seen this technique several times.

I’ve realized today while checking footprints that very small components will have a “drop factor”. Essentially, 0402 parts and the BAL-nRF1D03 components will be hard to hold and align. So much so that I suspect that I will need a 3:1 ratio. Drop 2 – 3 and get one installed.

I do like the Purple boards. I’ll likely do a trace antenna design this week and also have it made in case the PIFA doesn’t work out. I am having trouble though making sure that I have the correct impedance match for a trace. Seems 1.6mm FR4 would require 2.81mm wide trace in 1oz copper according to the calculators, but most designs I’ve seen are much narrower. I’m not 100% sure who to trust. Antenna’s still feel like black magic thus far.

There is a 10 pin expansion header with 7 GPIO outputs that can be configured to any type of communications bus in addition to the 10 pin SWD programmer header. It has built in RTD sensor inputs for never having to zero your power meter. An RTD is a temperature sensor, and this will be used to measure each strain gauge setup. This is similar to Rotor Power. This won’t be fully implemented initially as it’ll require calibration for every power meter and I will have to sort that process but it will be.