Guru
Joined: 05/10/2019
Location: United KingdomPosts: 7020
| Posted: 11:19am 09 Jun 2023 |
At 100mm square and with the corners already pretty clear it might be pretty easy to use the Hammond case for it. :)
The display pretty much fixes the overall size to about 100mm as the viewable area isn't central to the display PCB and it's nice to have it centered. An alternative approach might be to use the display in portrait, making a taller, narrower device. Whether that would still be as usable I don't know.
You could, perhaps, reduce PCB area by using something like the RP2040-Zero and, if there are insufficient IO pins (unlikely - it has 15 that are veroboard friendly plus another 5 if you are making a PCB or using blob board), use a resistor string and analogue input for the buttons. Stan would approve. :). You gain a USB-C socket too. :)
I've just measured the supply current to a "static" RP2040-Zero and it was 64mA. It has a linear regulator, but at 100mA the dropout voltage is only 50mV at 25 degrees C and only about 70mV at 125C. That means that a 3V7 battery, considered flat at about 3V2, shouldn't do too badly. Terminal voltage on lithium cells falls slowly then quickly at the endpoint, so battery life should be quite reasonable, I think. I'd anticipate the backlight being powered directly from the 3V7, of course.
Just a few thoughts... :)