that stupid thing everyone does differently

for the Raspberry PI

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smart shutdown attiny stuff, but with an spdt switch, also simple. low part counts, no schnick schnack.

The idea: have a "smart" SPDT switch that turns the Raspberry PI off by telling it to shutdown, then wait and kill the power, or turn it on by turning on the power. 

Also: must be open source.

  • 1 × TPS22917
  • 1 × attiny85 Microprocessors, Microcontrollers, DSPs / ARM, RISC-Based Microcontrollers
  • 1 × ht7333
  • 1 × switch Development Kits, Boards and Systems / Development Kits and Boards

  • breadboarding first prototype

    davedarko10/24/2018 at 12:14 0 comments

    To start with the first prototype I went with breakout boards for the chips, it's a bit botched, but fits. It was a bit tricky to find pin one on the TPS22917, but with the help of Alex I was able to decide on the right pin *hopefully*. On the left side is an HT7333 - I was thinking about using the AP2112K first, but the lower quiescent current of the HT7333 and general current consumption needs of the Attiny brought me to the holtek chip instead. 

  • hardware decisions

    davedarko10/10/2018 at 08:12 4 comments

    At first I thought I would slap an n-channel MOSFET to an attiny85, switch low-side (as in cut off the ground of PI) and call it a day. Then @Alex said high-side switching makes more sense, but complicates things. For a start you need a p-channel MOSFET instead AND to switch it off you need an extra transistor when your Attiny runs on 3.3V to achieve the voltage level that you're switching. 

    I learned a lot yesterday just by talking over whatsapp with Alex, while we were kind of distracted by the live stream of the "unexpected maker". In the end I found a chip called TPS22917, that Alex waved through as a "possible/passable candidate". This way I don't need a mosfet and a transistor etc. 

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