DrAzzy:
Wiring on the red activity LED is wrong too.
Don't level shift it, and CS is active low, so you want the negative side of the LED connected to CS before the level shifter, through a 1k resistor, with other end tied to 5v.
Don't feed the nano with 9v, feed it with a regulated 5v direct to the Vcc pin.
While I don't disagree with what you're saying, the schematic for the microSD portion (including the red LED), is pulled straight from the adafruit microSD breakout schematic they have on their site (link here). For the breadboard prototypes, I've just been using the prebuilt breakout cards with these connections to a nano and everything has been working.
Regulating with 5v does make a lot more sense. Take load off of the nano regulator and already have a regulator that's sole purpose is powering the nano. The main reason was that I have a bunch of the 9v regulators on hand, but it would be worth it to buy the 5v versions. Swapping in a 5v regulator would also help clean up a few extraneous traces as well.
JohnRob:
I would consider moving the input connector to where U1 is and moving the U1 etc up to next to the SD card. It just seems the major input traces end up at the bottom of the board.
Where ever the input connector lands, you need to add 0.1µF from each input pin to ground. You need to have the resulting "cluster" in a very tight layout. You should also have your regulator in the same area, keeping all the "power" components close to each other with a ground plane around it (i.e. the above mentioned ground pour)
On your led and button I/O you will need to put capacitors resistors and a zener on each one. If not you will slide across the seat touch a button and the ESD will fry your Nano.
Automotive +12V has some nasty characteristics. There are fast high voltage spikes and some lower longer ones. It also runs from 8V starting to 15V (intermittent) charging. Can your regulator handle the power at the higher voltages?
I agree, moving U1 up and the input connector down would clean up quite a few connections.
On the "input connector", the only real inputs are the input +12v vehicle power, vehicle CAN_High, and vehicle CAN_Low. The "+12v" and VLV_PWM pins are actually outputs to the exhaust valve. So the input VEHPWR_IN+ needs a 0.1 uF to ground. Do the incoming CAN_High and CAN_Low lines also need these caps since they aren't power traces?
Do you have any schematic examples of the resistor, cap, zener protection? The RC filter part of it makes sense, but I'm seeing a few different setups with standard zeners and TVSs and don't know how their performance compares.
The regulator should be fine - input voltage specs from 8v to 28v.
DVDdoug:
Try not to "push" the manufacturer to their limits on trace widths, gaps, or vias. It's easier to make a board with fat traces with plenty of space-in between. You are less likely to get a defective board, plus you are less likely to create a solder bridge or to damage the board during soldering/assembly/testing.
No time to do it right the 1st time, but there's always time to do it over!
Fair enough. I don't have any real hard size limitations on the board, so it's definitely doable to add a little more space between traces and maybe widen them up a bit.
:
and I thought it was just the company I work for that operates in that manner! Never enough time at the start and the 0.01% cost increase for the more robust part isn't worth it.........then when part A doesn't work out near the finish line, it's a rush to fix it and end up paying 50% more for part B that would've only been a 0.01% cost increase at the beginning.
Working on including the changes and improvements suggested here and I'll post an updated version when done for further review.
- I'm not sure if the '2596's in those are counterfeit, or if they just get a much better price than we do for the chip. BTW the LM2596 has no short protection. If you short the output, the LM2596 chip cracks open and emits smoke and sometimes a brief puff of flame, it's somewhat impressive.