HOW THE BIKE LIGHT WORKS
The circuit has two states which it alternates between. In each of the states one
of the LEDs is on while the other is off.
Q1 is turned on which connects LED1
and C1 to 0V. This turns LED1 on and
C1 starts to charge through the
resistor R1 causing the voltage across
it to increase (it starts at less than
0.7V). The voltage at the base of Q2
starts to rise as C1 charges as they
are both connected to each other.
As C1 has less than 0.7V across it Q2
is turned off. This means LED2 is not
connected to 0V and is therefore
turned off. C2 (which has more than
0.7V across it) is gradually discharging
into the base of Q1.
This continues until the C1 has
sufficient charge to produce a voltage
>0.7V on the base of Q2, which causes
it to turn on.
Batteries
LED2
R3
R2
C2
Q2
R1
C1
Q1
LED1
V+
R3
R1
C1
LED1
0V
V+
R3
R2
C2
LED2
0V
State 1 (see picture above):
