Electronics > Beginners

Opinions on a begginer made circuit

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GreySkull:
Hello everybody!

    As well as being new to this forum (but not new to the EEVBlog Youtube channel), I'm also pretty much new to making actual circuits with proper schematics and am still learning more advanced electronics. Thus, I had no other place to ask this but here. I have made a circuit based on the ATMega328P that would test some proprietary devices (let's call them stations). The main testing is done on a relay. I am testing diode polarity and coil resistance and if both are good then I will test the contacts of said relay (should be <0.5 ohms). My first prototype of this circuit works pretty well but it was very loosely made. No protections, single rail design and other bad practices. So I decided to amp it up a bit and make it a more permanent design with a PCB and everything.
    I would like some opinions on this circuit and if I can/should improve it anyway. This is not a production circuit so the standards are not very high at all (circuit attached).

Thank you!
   

Kleinstein:
I don't see anything really sensitive like a 24 bit ADC. So there is little to no need to use separate regulators for the relays and the µC. Using just a single supply makes thinks easier as there is no worry about one supply coming up earlier than the other.

Similar I see no need for the opto-couplers, just the transistors are good enough if the layout is no horribly wrong.

Depending in the wire / trace length the I2C interface might want external pull ups. Only the µC internal ones are rather weak. It may work, but just barely. So a board should have pads for external ones, just in case.

It looks like the µC internal ADC is used - so a filter cap at the reference pin is usually a good idea - just in case, one may not need to populate.
The µC usually wants 2 decoupling caps close to the chip - not sure if the layout allows the regulators close enough to the chip. So normally one has caps at the µC and the regulators.  Usually there is no need for 10 µF behind the regulators. It's more useful to have such caps before the regulator together with a diode to prevent reverse polarity.

GreySkull:
Thank you Kleinstein.

    I'll remake the circuit above, considering everything you said. Should I calculate the value of the pull-up resistors for the I2C bus or just ballpark it?
    I will also add decoupling caps between all three power pins of the µC as well as the filter for the AREF.

Thank you very much!

ebclr:
I would change relays to 24Vdc and use a switched regulator instead of 7805

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