more pov yoyo cost research

scale of 50 yoyos. project will be working on over the next month by dan fourie, laura shumaker, and I as a for-fun project spawned out of an idea my for-grades 2.008 team passed over.

functional parameters:
yoyo with integrated persistence-of-vision display

design parameters:
as of right now, for each side:

  • 5 LED display, similar to (josh gordonson and zach banks, fellow mit students) earlier work:
  • Goals: user-friendly and mod-friendly
  • Two buttons, high enough that can be accessed by pressing down on the clear thermoformed plastic cover over the circuitboard (similar to plastic water bottle in feel)
    • on/off power button(decided against the centrifugal switch designed by paulina mustafa, another classsmate, for their iron man arc reactor yoyo, because gives user option to operate pov-display without spinning the yoyo for a more stable display)
    • “change text displayed” button, and you can change the display by holding it up to your monitor ala This method means the user doesn’t need to have special cables to change the displayed text, and we don’t need a complicated / non-intuitive button interface.
    • 8pin: $14, 14pin: $17
      • if we order pcbs, can have holes for people to stick FTDI or ISP headers in, so people don’t need to solder little wires straight to the microcontroller if they want to edit or update the firmware on the ucontroller (or make a clamp breadboard) or buy one of the clamp programmers 
      • can have another mode (hold down button longer?) to change the flicker rate, since we’ll be using internal microcontroller clock which is RC and due to manufacturing variability only accurate to +- 10%
      • discarded option: right-angle button which sticks out side of yoyo. more complicated injection molds and I was worried if it’d be structural enough, since solder joints would be taking the strain. Seemed most likely to fail after repeated use.
  • PCB should snap fit in, so people can mill their own pcb’s and swap out the pcb if wanted
  • Rectangular PCB should fit, so it’s easier to panelize and easier for people to make their own board (can etch and shear off one side instead of having to have a mill and mill a circular board, although circular boards look cool .___.)
  • Ideally PCB is single-sided
  • run off a 3v button cell and contain a spare so people can go longer without ordering their own.
    • pcb serves as cell-holder, batteries should snap fit in to further simplify mechanical design
    • TODO not sure how batteries will be electrically connected to the board
  • for changing the battery / updating the firmware, top half of each side will be removable via a notch on the side
  • assembly: teach a microcontroller series and have people assemble two and keep one?

–maybe have a fourth state changing the flicker rate, in case a specific microcontroller’s clock is off (on/off/text programming/flickr rate programming)

cost estimate: 
$4.30 for two attiny85’s off of digikey, + shipping. || $2.96 for each attiny88 ($6).
cheap power-hungry LED, well.

Circuit: Shane’s interior-routed circuitboard

( cost ~$50 + shipping for 12 of them off of myropcb. Ladyada has a cost calculator for multiple suppliers and comments for each supplier:
That’s like $12 for each yoyo.

So uh… Maybe instead I will sink $80 into buying my own 1/64” and 1/32” spindles for the modela (each good for ~50 boards).
$2 per yoyo
ebay: $25 for 3x 9” by 12” FR4 board. Est.: our boards max 2” diam, so 1.5” square is 6×8 = 48 boards. So maybe $50 for 96 boards, or about
$1 copperclad per yoyo

75c ea @ 100 off of digikey. (need 200). or ebay, 100 for $7 incl shipping. $14 / 50 = 30c per yoyo. but late shipping…! may be too late for the semester
$3 per yoyo.

phototransistor: 28c each @ 100.
$1.20 per yoyo.

10k resistor, 50kohm, 5x zero ohm, 4x 500 ohm, 1uF cap.
14c each @ 100, cap
0.017 @ 100, 10k, 50k
0.01292 @ 250, total 400 needed, 500ohm
total 500 needed
0.00676 @ 500, total 500 needed, zero ohm
(this is if pov circuit does NOT need any resistors etc. ala , these are all for voxel light-programming)
total = .14*2 + 0.017*6 + 0.013*4 + 0.007*5 = 0.469
About 50c per yoyo. these are all 1206 packaging!

CR927, 4 batteries each, 200 total: $22, 30 mAh, used in blinkies
44c ea. yoyo
(alternative: rechargeable ones, $1.44 ea 55 mAh TINY 6.8mm diam, with solder tabs: $1.29 ea 48mAh 12 mm diam, $1.71 550mAh 23 mm diam
octopart search:

accelerometers 0.67 ea @ 100,, as used by
Indeed mill-able on the modela — 0.5mm gap, 0.3mm pad — DFN package
25 mil pins (15.6 mil gap and 10 mil pad/trace) — for modella, can achieve. aka 0.398 mm gap / 0.254 mm pad

$1.40 per yoyo

unless I figure out how to make accelerometers — see, and the borked link is J. Doscher, Innovations in Acceleration Sensing Using Surface Micromachining
— I’ll just pre-program the flickr rate (and make it adjustable via the light-serial-programming protocol?)

total: $15 per yoyo + some digikey shipping costs, so close to $17 each if we count the aluminum molds and injection molding / thermoforming raw mats as free (due to 2.008). and of course free labor XD

Previous research:
If we use those super-efficient LEDs, they are 30c each if we buy 400 (50 yoyos * 8 = 400 LEDs).
( via
x8 = $3 (if we include shipping)
Total = $118 + $10 shipping (so upward bound of $130)
So, about $2.60 per yoyo

3V Batteries — batteries are somewhere around $15 / 100 on ebay w/ free shipping, so $0.30 per yoyo)
 if we want them (I don’t think we do, we should design this into our mold or PCB) holders would be $1.50 each

Microcontroller ~$1.50 each, maybe $10 for shipping, aka $1.70 per yoyo

Here is how the “spin-activation” would work:

So, at 50 yoyo’s, we’re looking at $6 each which is over our budget. However, I’m confident if we look a bit harder we can get the prices down to $5 each.



Thursday: [everyone] finish the CAD for the molds
Friday: [nancy] check the dims / tolerances with Pat and Dave
Then CAM over the weekend Saturday, say meet for dinner on putz @ 5pm and then CAM (putzgiving is Sunday). Order electrical parts.
Hopefully mill / turn the molds over Mon – Wed before thanksgiving.
Finish electrical design -> gerber and programming over thanksgiving break and order pcbs if ordering them. by 26th
And injection mold / thermoform the week after (done by Friday December 2nd).
Assembly done by Dec 9th.

PoV no accelerometer notes:
I got nanopov example working this weekend — no accelerometer indeed means there’s an optimum speed the display wants to be waved at. wave it too fast and the image gets stretched out, too slow and the whole image isn’t displayed or it’s super-squished.

Oh, Tom went over this in his blog post:

One downside of this design is that there is no synchronisation between movement of the display and the display output. So if e.g. you wave it left-right-left all output is mirror-inverted half the time. Also, there is no stable, repeating image as you would get from a constantly rotating POV.

Hardware sharing / versioning, recent startups

A good number of hardware (well, electrical) online version control / sharing startups have come up recently.

  • – thoughts on smarter diff for EE
    • (version control. has good snapshot features for both board and bill of materials. has embeddable schematics. has nets. based around github, so social) 
    • “Online electronics design. Includes schematic diagrams, design hosting, parts library, and GitHub integration. Free for public open-source projects”
    • (version control and online ee viewing, board and schematic embedding. less of a social feel) 
    • “SolderPad is a place to share, discover and collaborate on electronic projects.” 
    • based off of github, so integrated
  • — no updates since october 2011?
    • (for embedding boards/schematics)
    • “CircuitBee provides a platform for you to share live versions of your circuit schematics on your websites, blogs or forums.”
    • (includes full hardware, not just ee, part sourcing) 
    • “The place to post and contribute to open-source hardware projects”

No doubt some form of open-source biology version control software will come into play soon too. But meanwhile the mechanical engineering side of things is looking a little bit neglected.

For online 3d model viewing, there are a few implementations, namely Thingiverse and 3dCADBrowser: (has assemblies, it looks like) (no embedding) (parts only, not assembled projects) (CAN be embedded!)
and a community around CAD:
another one, solidworks oriented:

Tools / raw materials search: Maybe we should do our startup around this, for integrating into one of the hardware version control platforms. Octopart is doing it for EE; now lets get the meche side done too. Then we can really have full integrated open source products sharing+version control online, and then life will be awesome 🙂
If open hardware hub got popular enough (they allow “links” when you submit parts for your project), that would be cool.
[Edit 6 Dec 2011: I found a few search engines. See]

Some more research on the subject: basically says “use all the normal software version control systems” (none of which are made for visual diffing)
For some snark on circuitbee: — so yea, circuitbee is not too useful
and some more snark on upverter / circuitbee for not making the extra effort to be open source themselves:
I think actually both circutibee and upverter are awesome and people are just being paranoid. -^-^- look at the long responses all the posts got from the founders o.o

to check out: another online circuits project:

China Makerspaces Visit Planning

I’m hoping to / planning on visiting Chinese makerspaces between end of term (12/19 for me, as I have not finals) and IAP (January 9).
[last updated: 11/24/2011]


  •, active as of november 2011
    • Saturdays, 14:00 – 16:30 (gcal sidebar)
    • ch.makerspace,
  •   SZDIY (shenzhen diy lab) active as of today november
    • 聚会Every Thursday / 每周四 19:00~22:00
    • 答:Seeedstudio 是深圳创客空间(Chaihuo)的主要赞助商,Chaihuo与SZDIY目前达成协议在特定时间(每周四晚)免费提供聚会场地给SZDIY社区使用来举办固定聚会
    • szdiyadm,


  • (both flamingoeda and gkfab have been subsumed by this, active as of october EDIT 11/24 active.)
    • meetings every Tuesday 20:00 to 22:00 (
    • open every day (according to email correspondence 22 nov 2011)
    • (last update july)
    • GKFab (not alive?)
    • We have weekly meeting at Tuesday night, and workshops at weekend. The space is opened every day, and you may want send us a mail before you come so we can make sure there is some members in the space
    • bjmakerspace,
  • yff — not sure if it’s actual makerspace looks corporate or spam. 


  • hackerspaces@gz (1 member?)
  • HTG (not active since 2010)
So looks like I should try to make Shanghai and Shenzhen, possibly Beijing although that’s covering a lot of ground in a week (mmm transportation costs). Guangzhou ones seem dead, which is a pity since that’s actually close to Shenzhen.

Ooh look! Someone I know is there! Star Simpson is apparently in China until January or so. And Maja Wichrowska (roomies shoutout!) is in Beijing for the semester. o.o Whoa. A lot of people I know are in China…
=== 1st, 1600 EST

  • (no response, dec 2011)
  • (no response, dec 2011)
  • Tokyo hackerspace (contacted via form):
    • Tokyo HackerSpace has an open meeting every Tuesday night, from 7 PM. 
    • Unlike most other hackerspaces, our members have very little free time, and as such, the space is not in constant use. Our members have a key, and can come any time they like, but its hard to predict when that will be.
    • I would highly suggest that you join our google group and introduce yourself and your schedule there: You’ll have a better chance at finding what everyone is up to, and when they can meet up.
? None in Taiwan nor Korea.
Visas and Passport Renewal
Proxy Chinese Visa service: e.g. (also does passport, also well-designed site)
Emergency Passport-ness:

I found a local Chinese company helping with visa application:
最便宜的机票+最优质的服务$170 total /1 year multiple entry。 If you fill out the form. Sounds reasonable. close to what they charge here.It is close to T. ~5 walking from T station. 2 stops from harvard (outbound).Go to the web site, fill out the file and print out. take 1 2×2 picture, the passport valid for 6 month and blank page .
经纬旅游 Boston 617-426-3123
electronicky shanzhai 山寨
and also awesome book: which is a fantastic romp around gaming culture, economics, and unions.
more on shanzhai
more on shenzhen
the linked article is account-walled so here is the article


1 Transportation FCU
55 Broadway
Cambridge, MA 02142
Driving Directions
 Send to Phone

1.16 mi

=== Options: personal tours. Or get MIT departmental backing (talk to Anne Hunter / Brandy Baker) for report publication, go in officially.

=== Oh hey look, someone wrote about MITERS in Chinese.
“not the game, nor is it the job, just love” Thanks, google translate 🙂

update 2 dec 2011
according to David of shanghai’s xinchejian, There are current 4 in China. OnionCapsule in Hangzhou is the first student lead hackerspace in the China Academy of Fine Art by a group of new media art students. They have a public performance scheduled on Dec 24. If visiting hackerspaces is one of the goal of your trip, I’d suggest you visit them at this event. It’s crazy party and a lot of fun.