Simple LED voltage BATTERY monitor

[newbie111]

BATTERY monitor

i found this diagram on the net

it says;

The LED produces orange when the red and green LEDs are illuminated.
The following circuit turns on the red LED below 10.5v
The orange LED illuminates between 10.5v and 11.6v.
The green LED illuminates above 11.6v


i have no idea how they got these figures

please show me how to calcualte this

thanks a lot

 

[mister_rf]

Re: BATTERY monitor

Vbattery
V green LED=1.7-2.5V
Vzener1=8.2V
Vzener2=11V
Vred LED=1.5-2V
Vbe=0.6V
Vbattery<V green LED + Vzener1 = 10-10.5V Green LED OFF, Red LED ON - total light RED
Vbattery>V green LED + Vzener1 = 10V-10.5V, Green LED ON, Red LED ON, total light ORANGE
Vbattery>Vzener2 + Vbe = 11.6V, BC547 ON, Uce< Vred LED, RED LED OFF , Green LED still ON, total light GREEN