In this post we learn how to make a running light or chasing light effect using only 3 LEDs, because 3 LEDs are the minimum number required for creating a valid or proper running LED effect.
How it Works
All the indicated 3 LEDs are illuminated when the inputs of gates N4 N6 are logic 1 and their outputs is logic 0 with the supply voltage on. The trigger threshold is first reached by one of the RC networks (R1+ P1/C1; R2/C2; R3/C3)
Assuming R1+P1/C1, Ouput of N1 is low, N4 is high and D1 is off.D2 lights up with N2 remaining at logic high and N5 at logic low when there is no voltage for R2/C2.
Similarly, D3 goes out with the output of N6 becoming 1 and N3 going low. At the input of N1, the logic of N3 is 0 after a delay in R1+P1/C1.
D1 lights with the output of N1 at high and N4 low. This process is repeated with one at first, then two, then one LED is lit again. An impression of running and flashing light is generated with light patterns shifting to one place at every step.
The unused gates of this 3 LED chaser circuit should be connected to the positive or negative supply rail. Both inverting gates (4049) or non inverting gates (4050) in the IC2 position. RC networks can be modified as per taste or for desired special effects.
The three remaining inverters in IC1 can be used as LED drivers/buffers in order to make the circuit smaller. IC2 can be ignored. Using a type 40106 is required in this case. High output LEDs must be used in this case as the LED currents are only 5 to 10 mA.
The current consumption of the circuit is 10uA without LEDs and operating from 15V.
With standard LEDs at 15V, the current consumption is equal to 30mA per LED.