I did not ignore it, I said that I'm already using Schottky diodes, but even with them there is no guarantee that the voltage drop will be low (because it also depends on the temperature).
My question was not about decreasing boot time or reflashing Arduino, that's why I didn't mention it. It's just not important, doesn't change anything in terms of circuit.
Vf for the diode is a miniumum of 0.8V and a maximum of 1.5V, both depending on the ambient temperature (see Datasheet, page 2)As it has a If of 10mA you need a resistor of (12V-1V)/10mA=1k1Ω in series with the diode.
The default position is that the Arduino is off, because GND isn't connected to ground.Because of this there is no voltage to get from that pin, because of this the switches doesn't get any voltage to turn on the optocouplers to turn the Arduino on.And thus The Arduino will never turn on.
If you want to blow the crap out of the opto's, then it's a fine circuit. Aka, resistors!But uhm, looks like a bazooka to kill a mosquito....
This would work, essentially the same thing, but removed redundant components, and added the current-limiting resistor
U3 can't be on unless one of the switches is pressed.did you rotate it by accident?
The Cathode on U3 isn't connected to ground on the battery, only GND on the Arduino.Follow the path from D8 to ground on the battery.Then follow the path from the emitter on U3 to ground on the battery.Also the phototransistor on U3 more or less shorts the battery when a button is pressed.
Again, resistors!And be aware the 4N35 can only do 50mA. And the CTR is only specified as 100% minimum (40% - 50% at extreme temperatures). So probably you can get away with less then 50mA for the opto LED but you can't be sure... And 50mA is just enough to power a Arduino without the LEDs removed etc. And that's no including the transmitter you probably want to hook up as well...