Saturday, December 8, 2012

Sorry for the Lack of Updates

I’d like to apologize for the lack of updates lately. I’ve been exceedingly busy at my day job. Long days testing has slowed the development of V3.

So where is it? The short is that V3 contains some bugs. I last had some zeroing issues which I believe is sorted by replacing the LM4140 with a voltage divider but it becomes hard to test this in conjunction with the magnetic pickup code. This is the major slowdown.

As a result I very much dislike the magnetic pickup. The code will need to be edited and trimmed I suspect. My research into gyro’s indicate they consume about 400 microamps. This isn’t much compared to the current consumption, but still adds to the target.

I’m actively exploring the nRF51422 and sorting out getting either an evaluation kit or development kit into Canada. After some back and forth NuHorizons seems that they thought they originally collected Canadian tax… however they do not. This means that a 99 dollar development kit costs 99 + 25 dollars shipping + either 19.45 or more likely 29.00 to process the customs and 13 dollars taxes totalling 166 dollars, or pay the 66 dollars for express shipping totalling 179 dollars as customs brokerage is included.

Symmetry Electronics seem a little more reasonable as the Fedex Express options are only 44 dollars and include brokerage processing, but it still totals 157 dollars for a 100 dollar dev kit.

While I had earlier mistaken that Digikey carries Nordic things they do carry Dynastream modules using the nRF24AP2. The difference is Digikey is express shipping for 8 dollars, or free ver 200 dollars and no brokerage! That would mean if they did sell Nordic products then it’s total cost would be 121 dollars shipped next day.

In terms of development costs 166 vs 157 vs 179 vs 121 shouldn’t be significant, however considering all the costs up until this point I’m about 2000 – 3000 dollars into development costs depending on if you include certain elements that I use (FR60 watch kit, Garmin Edge 500, programmers, tariff processing, etc). Keep that in mind if you think this is the cheap way out to getting a working power meter. (I could have bought 2 Quarqs or an SRM) That being said I’ve been pushing my budget for this project and there are huge limitations to the way it’s built right now.

The nRF51 would allow me to drive down the board / electronics costs. The AP2 Module is very expensive (25 dollars in low volume) compared with the cheap nRF51 ($2.63) and the AP2 module still requires a micro controller. Thought a finalized arduino style board is expensive, using an atmel atmega 32u4 is about $6.50. So even if I was to drop the pre-made board, the nRF51 still comes in cheaper by a significant margin.

Oh, and one more think nRF51422 (ANT+) is interchangeable with nRF51822 which means BTLE is possible without a significant change over in board design – in fact no change over! It’ll require different code (if BTLE ever pulls together a power meter profile).

To do:

Get V3 working well enough to make some videos of it working and post the board + code

Get nRF51 development equipment.


  1. I love what your doing on this blog, just wanted to add another additional benefit to using the nRF51 series, Nordic & ANT are making sure you don't even need to choose between BTLE/ANT+ :D

    1. The nRF51 series is a good option it seems, though harder to develop on a smaller scale as they are QFN packages which will require a reflow oven. The nRF51422 and the nRF51822 are both pin compatible, however they are coming out with a chip that does both ANT+ and BTLE on the same chip. I'm going to guess not at the same time though, as I think the target is to again maintain pin compatibility. Not that you'd likely have two devices receiving at the same time.

      I'm still trying to sort shipping into Canada on this kits. Looks like minimum cost is about 180 dollars if I order directly.