Powering Kids’ Toys By Hand


[Dominik’s] daughter had an old toy piano that she loved, but when the batteries started to die down, it played awful tones and sounded generally out of tune. While this is likely something our circuit bending friends might be interested in, [Dominik] preferred when things sounded more cheery.

He considered simply replacing the batteries, but it seemed like a far better idea to do away with them altogether. he hunted around for a solution, and eventually found one at the local IKEA store. He grabbed a LJUSA hand-powered flashlight and disassembled it, saving the crank and circuitry.

He installed the crank on the back side of his daughter’s piano, and mounted the electronic bits inside the toy’s shell. The crank spins a brushless motor, generating an AC current which is rectified to DC before being stored in a capacitor. He says that a 30 second crank will play just a few tunes, which isn’t ideal, though it is better than frequently replacing batteries.

[Thanks, Roger]

15 thoughts on “Powering Kids’ Toys By Hand

  1. Mike,
    you wrote
    “He says that a 30 second crank will play just a few tunes, which isn’t ideal…”
    are you serious… every dad will agree that this IS PERFECT!!!!
    My son has a few of this kind of toys (most presents of people which obviously dislike my wife an me). Believe me, listen to them for hours, days, weeks, before the batteries are going to die down, makes this solution awesome!
    And a very clean hack too!

  2. Install a supercapacitor (ultracapacitor) in place of the battery. Nice 2.7v “D” cell types with spade connectors on them for about $12-18 new. I got 30 for $8 each on eBay.

  3. Oh, after seeing the picture a little closer, this is about the same size cap as the ones in those “shake lights”, its also a supercap. The D cells I got were 310 Farads. Yes, full farads for those new to supercaps.

      1. Way too large for what you want to do. These are much better for trickle current to a clock or some sram. Another problem is the voltage. They’re usually rated for maybe 2.5V – 5V.

  4. you could go lithium.

    lifepo4 to be exact http://en.wikipedia.org/wiki/Lifepo4

    seeing the horror stories of lipo fires lifepo4 is safer especially with a child.

    you will still need a bms to control the charging and discharging.

    the most important is charging since the battery demand is very low you can run it for many days even months on a 10 amp hour lifepo4 battery.

    the next part you did not mention how many batteries it takes so you may need 2 lifepo4 cells and then what’s the minimum voltage needed to make it still sound ok.

    if you need 2 or more cells you may want to get smaller cells to get them in the case.

    the next thing with terrorism being a concern now a days if you do go on flights or travel internationally you may have issues with taking modified electronics on a plane or even internationally.

  5. As a hack fan I think this is pretty cool – very nice!

    As a parent, however, I think this is overengineering. I know my kid would get sick of cranking that thing and move over to a different toy.

    Seriously, unless you are going to put crank generators in every toy of your child’s, invest in a bundle of rechargeable batteries and have it over with!

    1. Agreed or hit the adaprter bin at the thrift and wire it for permanent power. Have done it many times as a circuit bender. Although on the same token I wonder what kinda crazy sounds you could get without a buffer/v regulator? I bet it would add a new dimension to the sounds you could get ;) But yeah, as a kid I LIKED electronics and the crank up stuff was discarded after the thanks pic to the gift giver lol. I can sell him some socks for his corn husk doll…

      on the other hand, kudos to the dad for actually giving a darn about his kid and trying to do something for him :)

  6. Cheap keyboards made in China have no quartz timing, hence tuning. As the battery dies the tuning goes flat and flatter. I found a one pound wonder called (Musical Fun) no other markings. Less than half of a normal key dip. A dozen tones that sound alike and 5 dreadfull tunes anyone would hate after a while.
    The name of the keyboard will be changed to Hacking Fun! I am wetting my fingertips in antisipation of it’s exposed ckt board.

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