New CAN Main Board
I made a few adjustments to the board layout and also to the pcb-gcode setting and milled another circuit board. This one turned out nicely, even with a couple hiccups. First, the board wasn’t taped to the fixture exactly level, so a corner with nothing important didn’t mill through the copper (it was only the board outline). Then a phantom E-stop signal stopped the machine before it was done and had to restart from the beginning (I upped the debounce value to correct this). I thought it was another beverage coaster while watching it mill, but let it finish and it turned out fine. I ran the drill routine with a .035″ bit and everything but the screw terminal block and power jack fit. I was able to make the terminal block fit by sanding down the edges of the pins, but the power jack I’ll just use some wires and plug later.
Since the majority of components fit, I soldered this one up to give me an idea of what the next round of changes need to be. The main one is to increase the size of the pads to make it easier to solder and to increase the isolation path around them to prevent bridges to the ground plane. I’ll also have to change the through holes to the right size in the Eagle component library I made. At least the spacings were all right so everything still fit. Another change will be to the text ratio so the thin areas of copper don’t peel off when milled. They probably would have been fine if the second pass wasn’t done, but whatever.
Anyways, the CAN Main board only contains the basic circuit to run a 18F4580 micrcocontroller with the MCP2551 CAN transceiver; power from a 7805, 20MHz crystal oscillator, ICD plug, reset button, CAN status LED and then the rest of the pins are brought out to female headers to plug in a shield. I also included an area for the CAN bus termination resistor and three capacitors with jumpers, and a place to connect the cable shielding to the board’s ground. There is a jumper to bypass the 7805 regulator to use a 5V wall wart directly which are more common these days.