How do you specify two separate power supplies in EAGLE?
I tried something like this schematic, but when I play with the board layout, I can't seem to make it recognize the arrows as two separate supplies (VDD for 5V and VMM for 12V motor supply).
I understand about naming nets, but the warning I get isn't about the net-- it's about two different nets connecting to the (common) supply.
You have to use two DIFFERENT "Vdd" symbols, since the special "supply" components cause a net to be named after them. That's why the "supply" libraries have so many components that pretty much look the same.
(I don't see a VMM, but there's a "+12V")
I am sure I'm doing a bunch of things wrong, but so far the "Rules Check" features have been appeased.
Up to 8 of these boards will be able to ride the same i2c bus. (Up to 16 if you use the pcf8574a variant on half of them.) This one doesn't do a separate latching step, but maybe a later design will. Yes, I know I'm not putting in room for a real heat sink on each Q0-Q7 package, I don't need that much dissipation. I may add a power jack alternative to the +12V pins of the cable header. The M hookups are at the right pitch for a block of screw terminals, or they can be soldered directly.
It looks pretty good to me, not that I have a lot of experience with motor drivers. Since you have lots of room, I'd make the "power" traces to the motors thicker...
While you may not need heatsinking, you can get a little "for free" by using copper "pours" on the PCB:
Yup, I was looking into the different options for pours and polygons for just this purpose. Are solid pours are better than hatched ones for heat? I should block the soldermask under the transistors as well, I imagine. That will come back from the board maker all tinned up like all other vias and pads, won't it?
I just wanted to get all the traces routed first. Sometimes it was hard to get EAGLE happy with new vias I had to introduce, such as those under the IC. It refused to see them as part of the net I was linking for a while.