Another update, despite the small increment this board has a lot of changes. Most noticeable is the switch to a digital isolator by Silicon Laboratories, which reduces part count and cost by about 3$/unit. Moved to micro usb too, which is nice since it seems to be more common. Was able to get some samples of both the isolator and usb connector from SI and FCI respectively, thanks!
Also worked out some software issues and got the LUFA HID bootloader working. I wanted to use the CDC bootloader so vanila avr dude could be used, but I was not able to get the code down below 4096 bytes without much sacrifice – despite removing about 400 bytes from the program the last hundred or so needed was going to be a lot more work. The HID bootloader is much smaller, and fits well in a 2k bootloader section, giving me 6k to work with for the user program, which is more than enough. I should have about another 1500 bytes to add more functionality.
- Digital isolators replacing optical isolators
- Somewhat better routing, pads
- larger pads for mcu & oscilator should help asm
- Support for LUFA’s HID bootloader
- the reset command ‘r’ now restarts to the bootloader
- currently no HW bootloader jumper – only software bootloader start
- micro-usb header vs mini
- matches ras pi
- seems more common anyway
- easier to solder – has guide holes
- 3 mount holes at corners
Still much to do, haven’t tested the isolator yet. I think i need to pick new caps too, pretty sure I have been getting 10v max ones when i intend for the high side to work up to ~28V.
Here is a shot of the PCB and the in progress board, partly populated as i was working on mcu code:
