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Hey guys, I'm a developer trying to learn PCB design and advanced hardware design and needed a place to start. I've designed a very basic clock with a Atmel Atmega328P-AU and from checking out some reference designs.

This design is my first ever design so not so great on rules and general design principles. I would like to be sure that this is a functional project rather than a pretty one. Are my connections correct? Is the 7 segment display wired correctly, is the DS1307 going to work? Can I connect MOSI, MISO and SCK to test pads on the PCB and use it to cleanly program the system effectively?

Please let me know of anything stupid I've done or any resources that can help me improve.

Thank you for your time everyone!

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    \$\begingroup\$ You seem to be copying the atrocious "blocky" schematic style. See this answer for an example of how such a schematic should look to be readable. I know that everyone and their dog is blindly using this "bunch of rectangular sub-blocks" style, but it's an abomination, and is done without understanding of what schematics are. \$\endgroup\$ Commented Feb 25 at 22:58
  • \$\begingroup\$ Where did this "little boxes" schematic style come from? Is it encouraged or imposed by EasyEDA? I think I've only seen it in the past few months. \$\endgroup\$ Commented Feb 25 at 23:05
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    \$\begingroup\$ I think this is exactly the same problem we have in software development with abstractions. Too much abstraction or abstraction in the wrong places and I have to dig through 20 classes and functions to find out what’s actually happening. Too little abstraction and I’m sitting in front of a 1000 line function and have no idea what’s going on. Not to mention re-use. The challenge (the art) is to find a middle ground. \$\endgroup\$
    – Michael
    Commented Feb 26 at 7:46
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    \$\begingroup\$ All grounds should face down. \$\endgroup\$ Commented Feb 26 at 16:24
  • \$\begingroup\$ @PeterBennett: I've seen that style many times over many years. There's a difference between designing a schematic to be easy to inspect purely visually without a cross reference, designing to be visually inspected with the aid of separate or embedded cross-reference information, or designing for inspection via tools that can auto-highlight selected nets. \$\endgroup\$
    – supercat
    Commented Feb 26 at 16:51

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The digit power circuit will not work as drawn. You need to flip the transistors around and reduce the base resistor values by a factor of ~20.

Edit: since you're multiplexing, the power and thermal requirements are a lot more relaxed. However a linear regulator is not a great choice in this application as the dropout voltage precludes operation much below a Vin of 4V (3.3 Vout + 0.250 dropout + 0.4 D1 Vf) so you will need 4 cells to get any usable life out of the circuit. Your efficiency at 6V Vin is 55% which for a battery powered device is unnecessary, especially when alternatives exist. I would use a different regulator, either a switching buck or buck/boost (my choice). Preferably something with built-in reverse polarity protection so you can get rid of D1.

There is no current limiting on your LED segments and LED3. There is no local decoupling capacitor on U3.

The blink LED will never illuminate in the polarity you have placed it in.

Capacitor U4 (?) may be too big for the regulator.

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    \$\begingroup\$ I believe the SW1 is always shorted, too, plus debounce is lacking. \$\endgroup\$ Commented Feb 26 at 11:01
  • \$\begingroup\$ @VladimirCravero Might sound "noob" but what do you mean when you say debounce is lacking? Thanks for the notice on the mistake with SW1, it's been fixed. \$\endgroup\$ Commented Feb 26 at 21:31
  • \$\begingroup\$ Thanks Vir for the message, it is definitely very helpful. I've been able to incorporate this feedback and fix the circuit significantly. If I'm looking for more help/ feedback should I open a new question or edit this one? Where can I learn more about right way to power this circuit, any reference designs or projects I could learn from? \$\endgroup\$ Commented Feb 26 at 21:35
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    \$\begingroup\$ Edit the original question and attach the new schematic (leave the old one up). Glad you found it helpful. Most switching converters have "recommended application" schematics that you are supposed to basically copy into your design. Or buy a complete module and drop it in. \$\endgroup\$
    – vir
    Commented Feb 26 at 21:49
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    \$\begingroup\$ @MustansirGodhrawala when a mechanical contact (eg a push button) is closed or opened, it toggles quickly between the two states before resting. This is called bouncing; there are ways to avoid this problem; just search on the web as this is a widely understood and easy topic. \$\endgroup\$ Commented Feb 27 at 8:18

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