Hi Again
Actually, this is what I said:
Before you plan to power anything off the USB port(s) I suggest you learn their power capabilities. The 5 volt power from a USB port is limited and one small boo boo can render the port dead.
Attached is a pin-out drawing of a USB 2.0 port. As you can see there really isn't much to it. Pin 1 is 5 volts, pins 2 & 3 are data and pin 4 is ground. So yes, there is +5 volts and ground available on the port. However, much unlike the +5 volts used within the rest of the PC the USB ports offer limited current. This is what the USB specifications have to say about it:
The USB 1.x and 2.0 specifications provide a 5 V supply on a single wire from which connected USB devices may draw power. The specification provides for no more than 5.25 V and no less than 4.75 V (5 V±5%) between the positive and negative bus power lines. For USB 2.0 the voltage supplied by low-powered hub ports is 4.4 V to 5.25 V.[32]
A unit load is defined as 100 mA in USB 2.0, and was raised to 150 mA in USB 3.0. A maximum of 5 unit loads (500 mA) can be drawn from a port in USB 2.0, which was raised to 6 (900 mA) in USB 3.0. There are two types of devices: low-power and high-power. Low-power devices draw at most 1 unit load, with minimum operating voltage of 4.4 V in USB 2.0, and 4 V in USB 3.0. High-power devices draw the maximum number of unit loads supported by the standard. All devices default as low-power but the device's software may request high-power as long as the power is available on the providing bus.
The above quote was
taken from here.
Pertaining to a USB 2.0 port what all of that comes down to is that unless request high current from a port the available current defaults to 100 mA. This is also subject to vary with different motherboards. Some motherboards offer over current protection while some don't. Much of it becomes a crap shoot.
There are countless articles out there on powering things from the USB ports of a computer. The problem is and what many fail to mention is if an enthusiast manages to short the 5 volts there will be a tiny spark and a good, very good chance the port will be rendered useless. Nothing wrong with using a port for power, however, you have to understand the USB port and know its limitations. That was my point.
As to the use of the 555 timer chip. The 555 has been around a long time. Extremely versatile little 8 pin chip for a host of timing (and other) applications. The 555 will easily act as a "Delay On" timer where when power (or a trigger) is applied the output can be delayed for a given period of time. That output can drive a small relay or a LED. Several examples of using the 555 configured for delay on
can be found here.
So lighting a few LEDs with a delay following a trigger is no problem. However, when we begin adding other timed functions then things can become more complex.
What I suggest is that you find yourself a small prototyping bread board and begin to experiment with a few 555 chips and a handful of components. Anyone here will likely be happy to help you along providing small starter circuits or linking to circuits.
Ron