I designed my first electronics project and I'd be thankful if you could give me any feedback on it.
I'm specially looking for any beginner mistakes, anything wrong or inefficient with my circuit, and on the way I built the schematic.
The project is a kitchen timer controlled by a Arduino. It has three timers that can run at the same time and it beeps when it reaches zero. It is powered from the wall, but when it's disconnected a battery must assume, without rebooting the timer.
The first schematic is the power supply. If connected to the wall, it should not use power from the battery, but it must switch to the battery if disconnected.
The second schematic contains the microcontroller and the switches and buttons used to control the timer.
The third schematic contains the display.
I understand that evaluating a schematic is a lot to ask, so I'm really thankful for any feedback.
I'm very grateful to everyone who took their time to comment on my schematic. I don't have any engineer friends around so your feedback is highly valuable.
I tried to make the changes according to what you suggested. I haven't tried it on the breadboard yet, so I'm not sure if everything will work. I still need to make a few tests to find out the best value for R5.
Here's the updated schematic:
Kudos for using a refdes (reference designator) for (most) components. Especially if you want to discuss a schematic they're needed for decent communication.
The power supply
This is a long list, but I think you did a fine job, considering it's your first project. I've seen much worse schematics. Success!
edit Re the update of the question
Your circuit around Q1 and D3 is not quite OK: the battery will feed the LED, but not the rest of the circuit. I'm not sure the LED as battery indicator is a good idea: especially with battery power you have to be economical, and not waste power on a LED.
How about this: keep the diodes like in your first version, but control the LED from the microcontroller. Use one of the free pins to detect the presence of the 12 V through a 5 V zener diode and a series resistor. You can then blink the LED when you're running on battery power. A short flash once every second is much more economical.