In many situations, whenever a running light effect is required, a wooden wheel switch is needed. The wheel is driven by a motor which normally connects three switches, one by one producing a running light effects. Such a switching is very bulky and troublesome.
Here is a simple electronic project “Running light circuit” with a very few components but which is equally effective.
Circuit Description of Running Light Circuit
In the circuit running light all transistors remain on except one which is off. This off sequence ‘travels’ through each transistor. Let us assume that T1 is off and T2, T3 are on. As T3 is on its collector voltage is low, so the base voltage of T1 is low as long as capacitor C3is discharged. Now capacitor C3 charges slowly through R1, as a result of which base voltage of T1 rises. As soon as it crosses the cut-in voltage, T1 turns on and its collector voltage drops. This lower voltage applies a negative bias through capacitor C1 to the base of T2 to turn it off. Now the next sequence is T3 off and T1, T2 on.
The transistor that is off has an increased collector which is used to trigger the SCRs. The triggering voltage is adjusted to the minimum to avoid false triggering. The SCRs get off by natural commutation. One end of each lamp is directly connected to the 230V AC supply while the other ends of the bulbs are connected to SCRs.
The SCR switching option is for low-power lamps (less than 100 Watts) or else we can use relay switches.
Sometimes when we switch-on the circuit running light all three transistors remain on, as a result of which running off sequence is held up. In this case, any one transistor is required to be turned off momentarily by shorting its base to the ground. A pushbutton switch can be connected between base and ground of first transistor for this purpose.
PARTS LIST OF RUNNING LIGHT CIRCUIT
Resistor (all ¼-watt, ± 5% Carbon)
R1, R4, R7 = 47 KΩ
R2, R5, R8 = 1 KΩ
R3, R6, R9 = 33 KΩ
VR1 – VR3 = 10 KΩ
VR4 – VR6 = 1 K Ω
C1 – C3 = 25 µF/25V
T1, T2 = BC147B
T3 = BC148B
SCR1 – SCR3 = TYN604
LED1 – LED3 = 5mm dia circular LEDs
LAMP1 – LAMP3 = >100 Watts