I'm very newbie in electronics, so, I kindly asking the community to review my schematic. This is my most advanced project I ever did and I'm really unsure about particular points in my scheme and about overall design.
What I'm doing is a multi-channel DC-motor controller with external powering. The motors will be small 5v or so DC motors with current draw about few hundreds mA.
Here what about I'm unsure:
Is it correct to connect ULN2803 in parallel to achieve more max current per channel? Is it correct in my particular scheme?
Is it enough to just put capacitor in parallel to each motor to perform low-pass filtering? Or I should add extra resistors for explicit RC-filter? If resistors required, then where I should put them: to Vcc line to ULN2803's pin?
Maybe I should put RC-filter between MCU and input of Darlington pair?
Do I need extra fly-back diode or ULN2803's internal diode would be enough?
How well the "USB part"? Won't it burn my PC's port? Will it even work o_O? Do I need to put resistors in between tx-rx and rx-tx lines? Will it work fine with external power source?
I added rectifier to make polarity-agnostic board. How lame it is?
How to make over-current protection? Do I even need to do it?
Is it fine that there no resistors near J1 port (ISP programming)?
Should I pull-down (pull-up?) unused MCU's pins or it will be fine to left them in air?
How critical for USART reliability to use crystal frequency 11.0592Mhz or multiple? Will it work fine with 16Mhz?