07/11/2021 at 08:44 •
My Pico is now installed in my new Checkmate A1500 Plus case! Minor alignment issues with the rightmost (nearest the PSU) stand offs, but the rest are OK.
The green LED is dim, but the forward voltage is likely very near the 3.3V drive voltage, giving very low current. Have a look at https://github.com/Neotron-Compute/Neotron-Pico/issues/46
07/07/2021 at 19:00 •
I put the broken board to one side and built up a second. It has a bodge putting a 10k between the base of the PNP and its pad. With this I can start up the Pico with the power switch, using the STM32 for debouncing, and then power it off with a long press!
I then tried to get video out of the Pico using the Pico SDK. Sadly, it's a mess because the SDK is really not designed for 12 bit colour. I'll need to hack it a bit to test the DAC properly.
07/01/2021 at 22:57 •
It tried to turn on the main DC PSU and I got a short circuit. After a bit more testing, I realised there's a dead short through the two transistors that pull the DC PSU enable line up to VDC when the STM32 output goes to 3.3V(VSB).
I added a resistor and tried to jump 3.3V into various points to test it in stages... and it went pop and now always short circuits, even with the transistors removed. I fear I put 12V into the STM32 and blew it up. Oh no!
06/28/2021 at 14:43 •
I designed this board without any other ATX board to compare to, or without an ATX case to measure up. I instead used the ATX 2.03 specification, which can be found online.
Today I obtained an old ATX case and I'm delighted to report that not only does it appear that all the screw holes line up, but that expansion cards mounted the "PCI" way around* are also pretty much centered on the expansion connections I picked.
Now I just need to design an expansion card! I'll probably do something with a through-hole prototyping area and get 20 or so made - they won't be very expensive. The trick will be in providing a screw hole that lines up with the kinds of expansion bracket you get from cheap 'scrap' PCI cards, as I don't know if you can buy that sort of thing separately. Note that ISA expansion card headers won't work as they bolt to the other side of the card.
* PCI cards have components facing 'down' away from the I/O area and hence the PCB aligns with the top edge of the bracket. ISA cards have components facing 'up' towards the I/O area and hence the PCB aligns with the bottom edge of the bracket. Neotron expansion slots are aligned for cards that are the 'PCI' way around.
06/27/2021 at 19:20 •
I got the first five v0.5.0 boards back. They look great! I tried soldering on the LQFP-32 STM32 (which I had in stock but JLCPCB did not), and it didn't go well.
The first one I soldered on rotated 90 degrees. Turns out the 'dot' is in the bottom left, not the top left. I'll have to get someone to fix that one with a hot air gun.
The second one went better, but was about 3 degrees out. This was enough to put the legs in between the pads on one side. No good.
The third seemed to go OK (thankfully - I only have one left!). So far, I've knocked up some firmware to blink the LEDs, check the UART and debounce the power button. It's all at https://github.com/neotron-compute/Neotron-BMC.
06/17/2021 at 16:44 •
The v0.5.0 PCB has been ordered from JLCPCB, with assembly for most SMD devices except:
* The CODEC
* The STM32
* The MCP23S17
* The RGB/HV ESD filter
* The RTC
I have those parts in stock at home and will hand-assemble them when the boards arrive.