QUESTION:- What is the one thing that has remained the same for countless ages?
ANSWER:- The way we turn on our PC's.
A PC uses what is called a "momentary switch" to initiate its boot up.
All right then cleaver, what's a momentary switch? eh? eh? what is it?
A momentary switch is a simple switch that, when pushed, creates a contact, and completes a circuit (closed) for a moment, then when released the switch opens again.
So if it opens again how does the computer stay on then! answer me that! if I had a hoover with a momentary switch I would have to hold it in while I cleaned under the couch! Ah-ha! gocha, didn't I?
NOOO! because a PC doesn't need to have it pushed in all the time, let me explain..........
Your PSU (power supply unit) outputs +5 volts on a specific pin on the motherboard the (+5VSB) when ever
it's plugged in and turned on.
This voltage is used to power your motherboards power control circuitry so that i can turn on when the BIOS tells it to (the boot up programme) or when you press the button.
The power button is nothing more then a momentary push button switch.
When you press it, your motherboard's power control circuitry connects the PS_ON lead to ground, then the PSU turns on fully up and provides power to all pins connected to the power supply unit.
Then it sends a Ready signal to the motherboard once it is fully powered up, so that the system only starts after the Power Supply Unit is ready.
But because this system is automated all it needs is a signal to start the sequence and the rest follows while completing certain commands in a pre determined order, and the PC boots up and starts.
Step 1: TURN ME ON! Ooooh Arhhh! (stop That!)
This is an example of a momentary switch, there are hundreds literally.
one of my previous instructables shows how to turn on your pc by inserting a plastic card in a slot which hits a momentary switch at the end.
Two wires lead to your momentary switch on your PC, these wires can be connected to anything you like as long as it creates a momentary contact.
The picture shows a simple diagram of the switch, as it is pressed the contacts touch and the circuit is closed.
Photos of the actual switch with wires attached, you will note the jazzy blue and white wires, which is not unusual but very stylish!
Notice the black flat connection to the motherboard at the other end
Other pictures show a switch in the on and off position and with a standard button attached, as on a computer.
So that's it, the momentary switch.