Table based Electronics or Rb Technology

 At books in the future:

Rb = 4.3/Ib

Rb = 11.3/Ib

Lets check and Learn to design Rb at Fire Alarm:

Lets design the Control Panel, Inside and Out.

Remote LED Indicator = 2.2 volts

by table:

12v 1k 2.2v(led)

6v 500ohms(led)

5v 330ohms(led)

By table, Rb = 100 Ohms..

Hfe = Beta/10

Hfe, use multimeter function NPN cbe or bce

Beta = 300

Ic = Vcc/Rc = Beta x Ib

+24-IbRb-0.7 = 0

Rb = 23.3/Ib

from Vcc/Rc = Beta x Ib

24/400/300=Ib

Ib = 0.0002A

Rb = 116.500 ohms

Rb = 100 Ohms, OK (lesser) 

NOTE: add latch for Alarm Bell

Thats it!