I'm looking at the 2560 schematic in Eagle. I'm very new to circuit design.
I understand all the connections coming off of the ATMEGA2560. What I don't understand is why there are no connections between the ATMEGA2560 and the ATMEGA8U2 and LP2985-33DBVR.
Why isn't the power schematic connected to everything else? It looks like 4 independent circuits with no connections.
I need to add hardware debouncing, motor controller, high speed ADC, quadratic encoder ICs, resistors and some other stuff. Debating on putting all of this on a custom shield or add all of it to the 2560 and doing a completely custom board. But first I'd like to understand how the Mega board works.
In EAGLE (and many other CAD packages), wires with the same signal name are connected, whether or not there is a physical line drawn on the schematic or not. Some diagrams make this more explict with a 'tag' symbol.
Power supply connections are especially common to leave unshown. For many library parts, the power supply pins aren't even put on the schematic unless explicitly requested (for instance, the LMV358 power pins aren't on the schematic.) They still end up connected to the appropriate nets based on their name in the symbol/device definition, though.
"For many library parts, the power supply pins aren't even put on the schematic unless explicitly requested (for instance, the LMV358 power pins aren't on the schematic.)"
I find this to be problematic - if the power pins are called Vcc and you are using +5V for the power trace name, then they no get connected.
If they are not shown, it is too easy to miss adding decoupling caps on them.
Luckily I discovered this in eagle (here in the forum) before getting burned on any designs: Right click the part and select Invoke (or, Edit:Invoke maybe?) and select the power pins so they show up on the schematic.
Also, use the Rules Checks (DRC & ERC) to check for any unconnected pins.