Originally Posted by trash

Looks like the guys above have got the 555 time theory covered. But maybe you need a little help with the ultra basics.

For anybody having trouble with electronics, there is one easy way to understand components and how they work. Every component has a mechanical equivalent. A friend who is a very good mechanic picks up circuit theory when I describe a component to him in mechanical terms.

Capacitors are like springs.
If you stretch a spring it stores energy, when you let it go, the potential energy discharges as kinetic energy.

An Inductor works like a flywheel.
A flywheel stores kinetic energy. A flywheel likes to remain at a constant velocity, any attempt to change that velocity is met with a resistance (or reactance). An inductor attempts to maintain a constant current.


Another example is to think of a capacitor as a water tank.
This time the resistor is like a tap which allows water to flow in.
The lower the resistance (tap open) the faster water flows into and out of the tank. The amount of water flowing through the pipe is the current. The volume of the tank is the capacity, the level of the water in the tank is the voltage and the amount of water the charge.

The 555 timer works a bit like the tank float in an automatic toilet.
The toilet tank fills slowly according to the tap setting (the resistor)
When the tank reaches a certain level, the valve opens, the toilet flushes. Another tap controls how fast the tank drains, (either a second resistor or the same resistor).
Finally when the tank is drained, the float opens the fill valve and the tank starts to fill again.

So the time it takes for the tank to fill and empty is controlled by two varibles. The setting of the taps, AND the size of the tank. If the tank is small, if fills quickly. If it is large, it fills slowly.

The time it takes for the cycle to complete is the frequency.

The dunny, like the 555 timer can be made to operate in many different ways.
A standard toilet charges and waits for a trigger (pull the chain) and then refills.