Hello guys, today we will talk about one important circuit. If you used a microcontroller before or digital electronics even if in analog you need to set the time to do something, to do that you have to use an Rc-circuit "resistor and capacitor " and you can control the time of the circuit by the equation: time= (the value of resistor)*(the value of capacitor).
Another way to give the time for your circuit by piezoelectric Oscillators
It’s very accurate so we use it in UC
requirements of these circuits 
battery 12v or adaptor
bush-Butten
1.5 volt led
1mf polarized capacitor
resistor 1 k ohm
Explanation of the circuit:
When you push the Butten A 5-volt battery will supply the Rc circuit by current the electrons want to close the circuit and go throw the resistor but the resistor will weaken the electrons, the second choice for the electrons is to go throw capacitor its less resistance, when electrons pass the capacitor track it should fall into capacitor full the cap by electrons then go to the battery again.
When you release the Butten (cut off the current), the capacitor will release the electrons that, it stored in it the load will consume the current in just 1 second, how do you know the time?
Simply, the Resistor is 1000ohm and capacitor is 1 mF so ((1000) *(1/1000)) = 1 s.
Explanation:
When you Bush-Butten the capacitor will charge as we explain above then when you release the Butten capacitor will act as a battery and supply the base by the current which will go throw 0.5k ohm resistor which will be biasing the transistor when the transistor turned on it will allow current go throw it so it will be short circuit the led will be off.
After the capacitor release all of its electrons the biasing of the transistor will be stopped so the transistor will be open circuit and the current will go throw led (led -on) this reaction is called transistor as not gate.
feel free to ask me any question:
Gmail: eng.darwishelectronics@gmail.com