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• breadboarding first prototype

  davedarko • 10/24/2018 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

  davedarko • 10/10/2018 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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