A-D 8800 bus card for prototyping

[Matthew Brugman]

I'm finally coming back around to this.  This is what I've come up with so far:

Highlights:

• Prototyping area of about 1" by 1.5"
  • 0.100" on center holes
• Bus addressing jumpers
• Level shifter for 3.3v
  • This is the only SMD device; I couldn't find a 6 channel through hole device that wasn't close to EOL that I liked
• Pin headers for 5V, 3.3V, GND, and the following signals:
  • Select (address matches jumpers)
  • SCL and SDA (more in a minute)
  • INP
  • OUT
  • WAIT
• I/O lines are buffered through a 8-bit to serial I2C.

The idea is that there will be a microcontroller connected (hence the level shifting).  The pin headers are extra long on the "back" side to allow for wirewrap prototyping (my usual preference).  Could always use Dupont jumpers and connect to a breadboard, I guess.

I haven't sent the gerbers to a board house yet.  Any comments on design?  Schematic is attached.

Thanks!

Matt

[Matthew Brugman]

Argh, the image is an older rev. Routing is cleaner in final, but layout is the same.   🤦‍♂️

[Tom Wilson]

I'm going to ask the obvious question... if the bus is connected directly to the I/O pins on the Due, isn't the bus 3.3v? So why the level shifter? Maybe I'm missing something (which is fine... I do that a lot.)

[Matthew Brugman]

Nope, you are correct, I was being careless. I’ve got two projects going that need custom PCBs. I usually procrastinate and then rush through the process because it’s it not my favorite thing to do. 

The other project needs the level shifter;  I had it in my mind because I couldn’t find one I liked for the application. I started the 8800 board first, and just got dumb. Sheesh. I’m sure I would’ve caught it later: I usually set them aside for a couple of days and review before sending them out. Either way, I would’ve had a “hey, wait a minute…” moment when I started the other board :D

I was stoked to share the concept with the group before sending to the board house. Patience, Matt 🤦‍♂️

[Matthew Brugman]

I got the shipment from the board house, but the delivery from Digikey with the parts is delayed.  Go figure :/

[Matthew Brugman]

I finally got the delayed shipment from that distributor in Thief River Falls.  (Normally, I order from them and get things within 3 days).  It took so long, that I actually spun a new rev of the board and got them from the board house before the parts arrived. 

Anyway, here is what an assembled board looks.  By assembled, I mean it's ready for prototyping.  The headers that look backwards (long pins on the back side of the board) are that way because I plan on wirewrapping the proto circuits.  I *just* finished soldering, so I still need to hit it with a toothbrush and IPA.