Build Instructions

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• 1

  Pre-amble

  In order to build our synthetic, electonic and thoroughly pointless jumping bean style novelty, we are going to need the following items:

  1 x latching button switch
  1 x sealed vibration motor
  1 x N-channel mosfet
  1 x lipo 3.7v 350mah pouch
  1 x lipo charger
  1 x ATTiny85 digispark clone

  I went with the sealed vibration motor after some tests with solenoids and other small motors as (amongst the options I tried) it appears to offer the most vibration for its size and, because it's a sealed mechanism we don't have to worry about the spinning shaft interferring with any of the other components.

  I chose the ATTiny85 digispark clone as, yes we could produce a pulse at a regular interval with discrete components - However the convenience, low cost and size of the ATTiny85 board makes it a very easy and attractive option. You could of course use any microcontroller of your choice (or yes, a 555).

  Nowadays we can get small Lipo pouches for not a lot of money and these are ideal for our purposes - Unfortunately this does mean we need a system to recharge these batteries which means we need a charger as well, however these are available in very small packages for very cheap so not too much of an issue.

• 2

  Build Notes

  First we'll program our microcontroller - You can obviously use any microcontroller you like but I am using a digispark clone from China (these are long out of production so this is realistically the only option to acquire them at this stage). If you are following along at home, again you can interface with the microcontroller of your choice however you want, if you too are using one of these ATtiny85 "boards" then there is a useful tutorial how to set up the Arduino IDE to use with the chip here: https://www.instructables.com/Digispark-Attiny-85-With-Arduino-IDE/ - This means you can upload the code (such as it is) over USB which is very convenient.
  

  There really is nothing to the code but here it is in case you need a starting point:

  I chose to also illuminate the built in LED on pin 1 so I could see the code working without the motor attached but do what you like, I'm not your dad.

  This operates the motor to make the device "jump" - I've set the interval to once a second in this instance because I want to submit this to the 1hz project comp, but you could introduce random delays etc. to make the movement more "realistic" if that's the sort of exciting life you lead.

  
  Next we can start wiring everything together, first I'm going to squash the mosfet against the digispark clone board like a dead bug in order to save space - I'm not really worried about heat in this circuit given the comparatively low amount of time the motor is actually operating (these motors are not engineered to be operated continuously anyway) and y'know, this is not high power stuff we're talking about. 

  I'm no electrician however so follow these instructions at your own risk and do your own research (I probably should have mentioned this earlier to be honest)

  After the wiring we should have something that looks along these lines:

  The layout being:

  and for those desperate for a schematic:

  The schematic here shows a arduino obviously but the key here is we are using a GPIO pin from any old microcontroller to operate an N-Channel Mosfet, so pick your poison basically. Also I forgot to include the charging circuit but you get the idea.

  Next I liberally applied some electrical tape to prevent shorts and keep the Lipo away from any pokey bits and we'll stuff it all into some flavour of container - I chose something vaguely bean shaped but use whatever you like.

  And that's it basically. Here's a video -

  Thrilling!

• 3

  Afterthoughts

  Altering the recipe: One of my goals on this build was to keep the size and weight down to a minimum, however on reflection the design is quite scalable - if you wanted to use a 24v motor / solenoid (for example) you could easily use this as a basis, you would need to upsize the power delivery and make sure you're using an appropriate mosfet, whilst also delivering a suitable voltage to the microcontroller (there might be some additions for safety needed as you increase in the voltage in the circuit, but that is beyond the scope of the discussion here) but broadly the design would be similar.

  Possible improvements:

  Because we have a microcontroller onboard, we can add features via code - I'll admit I don't have any good ideas what these features could be right now but the potential is there.

  One of the key factors in this novelty is going to be weight - The more weight we can remove, the more movement can be produced - I would like to get a better "jump" out of the bean. with this in mind, we could remove the charging board from the assembly, and instead keep it as a seperate item to charge the device as needed. The lipo pouch could also be replaced with a smaller, lighter version, assuming its got enough juice to operate the motor. 

  Ultimately I think creating a bespoke PCB intergrating most of the elements would produce the greatest weight saving, sadly I've got no experience with PCB design, but this might be a project for another day.

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