- How i can calculate the output power on pin 3 on each 555 Timer.
- I don't know how to calculate the Base Resistance on the transistor.
The 555 delivers a voltage on it's output, not a "power". The current flow through the output is dependent on the external circuit connected to it.
The output of the 2nd 555 will be at most 12V, and assume 2V over the LED, that will be 10V over the 390R resistor, and thus: 10V / 390R = 25mA.
Some conservative calculations for the NPN transistor:
It will never have to conduct more than twice the LED current, so assume a 50mA maximum current.
Hfe of a 2N3904 is probably much bigger then 200 (I have not checked it), and assume 200 is OK.
The current through the base of the NPN should then be 50mA / 200 = 250uA.
The base resistor has a voltage of around 11V over it, and 11V / 250uA = 44k Ohm.
You want to make sure you have enough current through the base, so I would start with 39kOhm, which is in the E12 table. But it's not ritical. 10k is also OK.
But Ian.M's use is much more common and needs less components. Just keep the second 555 in reset when it's not needed.
If you want to make a 555 oscillate with just one resistor and capacitor, then connect the resistor between the output and the timing capacitor, and don't use the the discharge pin. Then the capcitor will charge and discharge though that resistor.
Also:
Build it on a breadboard.
Have some fun with it.