At this stage IMU accuracy is less important that functionality.  

In order of likely utilization:

  • Accel: ability to wake/interrupt processor when accel rises about some arbitrary threshold.
  • Ability to keep gyro, and mags turned off, but accel on until needed – initially all the time.
  • Quaternion output.
  • Accuracy vs range.  My guess is that we need +/- 3G and that accuracy is good enough.
  • Pace detection:  the ability to know that the person is walking, as opposed to just moving around is useful. Accel-only pace detectors are pretty poor generally.  If there are pace detectors that use the full IMU it would be good to know.
  • If we find some really excellent full IMU ded'reckoning code then that could be a significant factor.
  • I think I will try to use off-the-shelf drivers for as much as possible, and just use my own work to help understand how the drivers function, unless there are no drivers, and then I'll have to make them.  Using off-the-shelf means better reliability.

I have been emailing nRF51822 module suppliers asking for pricing, availability and datasheets. The datasheets will be placed for now in Dewbly shared docsNordicModule data sheets. These are the replies.

From nRF nrf@freqchina.comXunTong Technology

Hi David,
Glad to get your email. this is Echo from XunTong Technology ,nice to know you.
About the datasheet of PTR5518, PTR5528 and PTR9018, see the file attaches, PTR5518 is CE and FCC is certificated, and PTR5528 and PTR9018 are not certificated.
For the Modules, we don’t programme the Chips NRF51822-QFAA, total 256K flash, 80K for BLE stack, others for your firmware.
David, no distributor in US,  you can send sample orders and small amount orders on Alibaba-Aliexpress store, for large Qty orders, let’s disscuss the details .
David,would you pls simply introduced your project and product, we have enginners for technical support for cusomer’s development.

Best regards 
Dear David,
Nice to get your inquiry. Please check my reply as :
1)      Unit Cost for LSN51822 as below .
Noted :
Standard MOQ and SPQ is 3K pcs. or multiple of 3K pcs.
*Price not included for courier charge*
Shipping Location from : Hong Kong
Payment in advance.
Normal Production Leadtime : 6-8 weeks or base on stock status
*we have below 100 pcs at this moment.
LSN51822 Module 
(obtained Bluetooth DID)
Qty. Price Idea
Below 100 pcs. / lot : USD 15.00
100 pcs. to 1K pcs./lot : USD 7.00
1K to 3K pcs/lot : USD 6.00
3K to 9K pcs./lot : USD 4.20
9K or 48K /lot : USD 3.90

2)      LN05 Module , not yet plan for Bluetooth approval.  We would like to start it if it can match with  some potential projects.
3)      Datasheet attached
4)      Can tell me more about  your company ,  project application , development schedule, Expected Annual Consumption …??
Thanks & have a nice day ~
Best Regards,
Danny Tsang
Li Seng Technology Limited
Hong Kong office:
Address: 9/F, Shiu Fung Hong Building, 239-241 Wing Lok Street, Sheung Wan, Hong Kong
Cellphone : (852) 9430-7943
Main : (852) 2540-8348
Fax : (852) 2547-5706
Shenzhen office 深圳:
地址 广东省, 深圳市, 南山區,南海大道,花样年美年广场, 19903
Mobile : (86) 136-0308-0321
Tel : (86) 755-2652-3481
Fax : (86) 755-2652-3494
No virus found in this message.
Checked by AVG –
Version: 2014.0.4570 / Virus Database: 3950/7568 – Release Date: 05/26/14
Hi David,
Thank you for your inquiry.
The samples are available now.
Sample price is U$8.- / FOB Korea.
MP(Mass Production) unit price is depending on the volume. (U$3.8 through U$4.8)
One reel q’ty is 500pcs as MOQ(Minimum Order Quantity)
What application are you considering and what is your yearly forcast quantity?
Please refer to the attached datasheet.
Should you have more questions please let me know.
Best regards.
Warren Choi
Director of Sales & Marketing
Tel : +82 (0)2-2619-9662 (Ext 170)

RE: Raytac MDBT40 & Nano Module Enquiry – Touchstone-Labs



2:06 AM (5 hours ago)

to me
Dear David:
Thank you for your mail. I am Sharon from Raytac.
Attached is data sheet for MDBT40 and Nano. Please find price table below for sample cost.
Unit Price (in USD)
BT 4.0 Module (128K)
$ 4.50
Sample Buy
Freight cost is excluded.
BT 4.0 Module (256K)
$ 4.90
BT 4.0 Module (256K)
$ 5.00
Due to large required demand, nano sample is now temporary out of stock. The next lot will be ready on the first week of June. Please let me know how many samples you may need so to reserve samples for you in advance.
Best Regards,



6:36 AM (52 minutes ago)

to me

I am Charlie@AceUni.

BLE51822C’s unit price for sample is 7USD, freight is not included.
FOB unit price for 1K is 4.95USD.

BLE51822C is comply with FCC and CE, but we do not apply the
certifications by now. We can help you do the final product FCC
certification. And it will cost about 2,000USD including all FCC fees.

The specifications are attached.

Best regards,


Alibaba advertises a 156mm x 156mm solar cell with 4.38 watt output. The space on Minitec enclosure for membrane keypad is 34.7mm x 19.6mm, or 680 mm2. The solar cell is 24336 mm2. 24336 / 680=35.8. 4.38 watts / 35.8 = about 120mW.

This LiPo battery is 160 mAh * 3.7V = 0.592 watt-hours. 0.592 watt-hours / 0.120 watts = 4.9 hours to charge the battery using a piece of the advertised solar cell in direct sun at the equator at noon if it’s cool. It won’t work out exactly like that but at least it’s a possibility.
The iPod nano 6 LCD is about 32 x 33, or 1070 mm2. If it was replaced with a solar cell the output might be around 0.2 watts.
I still think the OKW Minitec is best solution we have available to us now. It would be interesting to see how much power a solar cell on the front of it would provide in normal use (worn on the wrist with a short-sleeved shirt on a bright day with all the window coverings open).

The difference in quality between the 3D printed things, and the professionally made enclosures is huge. I’m pondering our enclosure choices:

  1. If we only make a few units, then it makes sense to use an off-the-shelf enclosure, even if the enclosure costs us $20+ a shot. It actually makes sense for us to buy some cool product like the iPod nano, or one of those flashy watches, tear-it-down, and jam in our own custom PCB. It makes sense as long as it isn’t more work than:
  2. Designing and printing our own enclosure. It will look crappy, but sometimes it’s possible to make a virtue out of a feature. e.g. make it look like tree bark? It makes sense to do this as long as it isn’t more work than:
  3. Using an off-the-shelf ugly box into which it is quick and easy to fit our PCB. Then we try to figure out some way to make it less odious with some sort of strap, or pouch. It might be possible to get a person who is handy with a needle and thread to make some clever kind of wrist strap.
  4. Focus on getting the PCB to work, and not worry about the enclosure. When it works, find some off the shelf plastic box like this, and use some duct tape, elastic, or other junk to make a wrist band.
3rd Party Module

This is a promising version – from Fujitsu.
This version from Laird is less expensive ($13 vs $17) and has some kind of “SmartBASIC” already installed to make it easier to use. Do you want SmartBASIC?

Wrist pouch:

M: possible enclosure for a clunker
$11.99 watch:
M: Can we buy enclosures from SKMEI and use them?
SUOXINI 833 Stylish 8-LED Blue Light Digit Stainless Steel Bracelet Wrist Watch (1 x CR2016)SUOXINI 833 Stylish 8-LED Blue Light Digit Stainless Steel Bracelet Wrist Watch (1 x CR2016)
HZ-323 Fashion LED Digital Bracelet Watch - Black (1 x CR2016)Multi-Function Digital Blue LED Wrist Watch - Brown (1 x CR2032)I really like this one but I bet is sucks juice.
Skmei 0805 Fashion Rectangle Dial LED Digital Wrist Watch - Black boring
72-LED Blue Light Matrix Stainless Steel Watch/Wristwatch (Silver)must suck power
Personalized Signature 3D Pedometer Smart Watch - Blacksimple, utilitarian strap idea.
Waterproof Resin Glass Dial Plastic Casing LED Digital Bracelet Wrist Watch - WhiteWaterproof Resin Glass Dial Plastic Casing LED Digital Bracelet Wrist Watch - White
RQ-05 Bluetooth Bracelet Watch Answer Call w/ Vibration + Mic + Speaker + Time + Cell Phone - Whitebluetooth phone
3D Fashionable Calorie Pedometer USB Flash Disk Multifunctional Sport Smart Watch - White simple strap idea
Snore stopper:
Snore Stopper Tool with Wrist Band (1 x AAA)  Clunkerrrrr
People tracker:
Photograph not to scaleTrackerPal Image Pretty..
iPod nano wrist thing:
Aluminum Bracelet Watch Band Wrist Cover Case for iPod Nano 6 6th Gen - Yellow
Mp4 watch:
Bluetooth watch:
Fashionable Bluetooth Watch w/ Caller Display
This is what a 3-D printed case looks like:
Misfit Shine:
Look how the magnetic clasp attaches to clothes.
Maybe we could buy iPod nano 6’s and use them for parts: enclosure, LCD screen, case, and there are wrist enclosures for them. 
Image #1
But probably too small.
Never mind; they’re $150. But interesting how they can be used as a wristwatch.
Buy Battery for Apple iPod Nano 6G MP3-Player #616-0531  I wonder what it’s dimensions are?
Good article. Good description of issues. 
“In that light, rings are just a crutch, the temporary technological bridge we need to walk away from hardware forever. For now, though, that bridge is made of nothing but hot air.”
My opinions: It’s “evolution” at work.
* Random, thoughtless mutations of successful (iPhone?) DNA have not yet produced branch of animals that have found their niche in the gizmo food chain – a niche that at least  allows them to live long enough to produce progeny.
* Rings/bracelets must have sufficient value – value that you can’t get, with less overall hassle, some other way. E.g.  I’ll wear an insulin pump. I won’t wear a tv remote.
* If I have to wear it & it’s visible, it better say something positive about me, or be very cheap and highly functional.