We don’t see ourselves wearing these pendants around, but we still enjoyed taking a look at the design. These are just two from a wide range of offerings meant to be worn around and recharged by the sun. But a cloudy day won’t ruing the fun; they can be topped off via USB as well. Parts lists and schematics are included in the assembly Instructables for both the Owl and the Heart.
[Marty] and [Robin], a brother and sister developement/design team, were showing them off at the Sector67 hackerspace in Madison, WI. The single integrated circuit used in both is an OpAmp responsible for managing the blinking. The heart board has a calculator-style solar cell which charges that 0.5F supercap. The Owl has just a 0.022F coin-type capacitor and features a different style of solar harvester. The six components around the cap are each individual solar cells. [Marty] told us that they pump out a ton of juice in direct sunlight, outperforming the calculator-style cell. The opposite is true indoors. But as we’ve seen before, indoor solar harvesting is a tough game.
Need even more bling around your neck? Check out these LED matrix pendants.
I was searching for shop with this little calculator sized solar cells, but with no luck. Can anyone tell me, where to get them?
http://www.digikey.com/catalog/en/partgroup/cpc1822/12993 4v @ 50 uA.
http://www.digikey.com/product-highlights/us/en/ixys-ixolar-solarbit/823 has higher currents/lower voltages. Note that most of those listed in that table will no longer be available when current stock is gone.
A cheap solar calculator?
Other than being smt, these are the bad boys they were using.
http://uk.rs-online.com/web/p/photodiodes/6520207/
Digikey stocks a range of amorphous silicon cells like calculators use.
http://www.digikey.com/product-detail/en/AM-1456CA/869-1002-ND/2165187
They work better indoors because the don’t need IR light to work well.
That owl is absolutely beautiful! The through-hole parts seem like they’d be a little prickly though. A surface-mount board with a smooth back might be more comfortable to wear. :)
We’ve found that you need to seal the boards if you want them to survive water and sweat. A thick coat of epoxy sealer also gives the through hole boards a smooth back.
Now make the heart sync the flashing with heartrate
The pieces have less than 10uA current budget for sensing and pattern generation. This puts strict limits on what a piece can do. I do have some ideas on how to fit heart beat sensing into this current budget, but haven’t had the time to test them yet.
Whilst I understand that through holes are necessary for easy assembly, I think that smd components would create nicer looking pendants….
Well then, go for it. They’ve got a shop, and they got SMD…
http://www.etsy.com/listing/118743601/blinking-purple-heart-electronic
I had to resort to buying Pound World solar calculators back in the day, still have a few here.
Ironically the solar panels probably outlasted the supercaps, these really don’t like overvoltage ie >2.5V for single units and will burn out in a year if you don’t add protection to them.
A good source for these is dead phones and cameras, a few of the early Nokias used a nano sized one on the board and later phones use an ORB cell that is essentially a fancy supercap with a polymer electrolyte.
Be careful when desoldering as they are very sensitive to heat and can explode if they get much above 250C; best to use Chipquik here.
Contrary to popular belief they are not as sensitive to polarity as you think, add 10K series resistor and leave overnight and the leakage drops down to single digit microamps ie it will hold a charge for weeks.
this is a new jewelry generation… i’m sure, soon this trend will gain popularity
the use of photodiodes is awesome!
I just visited Sector67 last week. Very nice space.
Hi, I also found that many old dead laser diodes used in DVD writers etc have a photodiode built into the laser can.
If you find one which measures 0.7V between pin and Gnd it is likely to be one of these, decanning it will net you
a nice little photodiode and if the remains of the broken LD get in the way it can be removed easily.
I’ve overdriven these and measured close to 8mA with a moderate amount of focussed light so if all else fails…. :-)
Also the ones used in Bluray lasers such as the KES400AAA are wideband (they have to be) so will respond from 800nm
to 350nm albeit with some variation whereas normal silicon PDs aren’t a lot of good past 600nm.
Peak photosensitivity for most solar cells is in the near infrared range which helpfully gets removed by the
filtering on linear fluorescents, but CCFLs can pass some.