Entry 21: Here We Go Round Again!

A project log for Aiie! - an embedded Apple //e emulator

A Teensy 4.1 running as an Apple //e

Jorj BauerJorj Bauer 07/31/2020 at 04:010 Comments

Well, it's official - the r7 (or "v7" as I apparently named it, since I'm mostly doing software stuff these days) Aiie board is off to OSH Park for prototype manufacturing.

There are some substantial changes in there. Amongst them:

  1. Serial display, of course, is a huge change. Performance continues to look great during initial development (huzzah for DMA transfers).
  2. I got rid of the Tall Dog adapter. As I mentioned before, I'd been using it because of the pins I needed from the Teensy 3.6. Now that it's a serial display, there's less need for the pins (which is good, seeing how the Teensy 4.1 has fewer pins than the 3.6).
  3. I added an audio jack that cuts off the speaker (mechanically).
  4. The battery voltage monitor is redesigned. The old version was just a voltage divider going to an analog pin; it's now fed by a P-channel MOSFET so I'm not draining the battery constantly while monitoring its voltage. Maybe I'll actually get it coded up and working the way I want this time.
  5. A USB jack for plugging in a keyboard. I've done basic testing and it works, although modifier keys behave a little unexpectedly. I opted to not add a lot of protection circuitry here, not sure if that's going to come back to bite me later...
  6. The ESP-01 now has its own power switch. And the correct pull-ups to be able to boot. I never got to the ESP-01 development I wanted on the old board because of CPU issues; I'm hoping that won't be a problem here. Regardless I figured I'd rather not have it draining the battery when I'm not using it - especially since the ESP-01 has a higher current draw than the Teensy 4.1 and display put together.
  7. I'm using a boost power module to run off of +5v, and regulate it back down to 3.3v where necessary. The old board ran straight off of the battery which lead to some issues with fluttering display brightness as the battery ran down.

I've also been playing with VGA output on the Teensy 4.1, trying to build a FlexIO output with the right timing. However, there aren't enough free pins for me to do that with this layout, and I've been delaying having prototype boards made while I'm fiddling with the VGA stuff - so I've put that on the back burner for now. Maybe v8 will have a serial display-or-VGA hardware option, or maybe the VGA version will wind up being something completely different. Or maybe I'll never get back to it! Who knows. :)

By the end of August, I expect I'll have three prototype boards in my hands with a pile of new components to populate. Then it's back to the software!