Looking for layout advice for industrial environment using ATMEGA328P

Question

I need some advice on the layout of my board.

I'm using Atmega328P and intend to use it in industrial environments.

The purpose is to take a 30Vdc max input and step down to 5V with LM317 to power the Atmega and other IC's.

A relay will use the input voltage and if needed a series resistor, the LEDs will be driven by ULN2003. The main idea is to make a reliable system for monitoring battery packs during charge, up to 65Vdc, and based on the voltage the relay will cut the charge off. The SMD buttons will make the configuration for the relay operation.

On the next version will try to make SMPS power suply instead of LM317, first I need to test the software in use and then make changes on pcb if needed.

Schematic

Layout

Answer 1

Schematic

• 30V -> 5V using a linear regulator: bad idea. Use a switch-mode regulator for large voltage differences. Assuming half of the 4·7 segments are on at any given time, and the 9 other LEDs are, too, and and each is set to 10 mA, then we got 230 mA. At a voltage difference of 25 V, that's nearly 6W of power that a linear regulator converts to heat. That thing will start to become unsustainably hot and – hopefully – shut itself down.
• The ULN2003A gives you nothing you actually need – it's a Darlington array, but you just need to sink some current. You'd be better served with discrete NPN transistors, or n-channel mosfets.
• Since MOSFETs are rarely as good in p-channel as in n-channel form, it's generally a better idea to use your microcontroller's GPIO to sink current, rather than sourcing it; i.e. connect your LEDs exactly the other way around and turn them on by pulling the output low.
• I don't know what "+C_BAT" and "-C_BAT" are, but I'm almost certain you're operating your opamps in a way that damages them: the input voltages must be within the supply voltages, and you specified V_Bat_ext to be up to 65V, but you're only dividing that by 10, and supply your opamp with 5V.
• C31 / C29: assuming you added these for noise reasons: they do (nearly) nothing. You need to add them after a series resistor, otherwise there's very little source impedance that would lead to a voltage drop for higher frequencies!
• You sprinkle things like D22 in a lot of places. I don't think that actually helps.

Layout

• Ground plane. Have it. Ground return paths are necessary, especially around your microcontroller, where you actually do have a "high-speedish" clock.
• Your design is far too crowded and is also lacking any option to safely mount it anywhere. Board space is relatively cheap, so make it twice as big, try to stay on exactly one layer with all your signals if possible
• Do not route analog signal lines across half the board. Re-arrange your analog signal processing (the opamps) to be close to the source of observation.