I understand how individual pins control different functions of digital devices, but today I realized I don’t understand how this works in small electronics. Is there a very small mechanical switch or is there a different mechanism going on when something is switched off and on?
In: Engineering
When you press the button, it mechanically closes two different circuits.
The first one triggers a pin on the CPU and then the CPU can run some code to sleep or wake or whatever it wants to do.
But what if the CPU has totally crashed? And you need to do a hard reset? Then there will be a complete separate analog circuit that runs a simple timer, and once the timer hits it’s set value, it will open and close a switch to physically turn the CPU off and back on again.
Part of the device is always on and is just monitoring some low level stuff including the power button. When it recieves this signal then it tells the rest of the system to turn on. Some chips can have such incredibly low power in a sleep mode that it would basically never drain the battery.
Transistors! A voltage (or lack thereof, depending of the type) at the base pin of a bipolar junction transistor will allow current to flow between the collector and emitter pins, acting like a switch!
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