Running LED
Two button control
Relay clock
Toggle on-off
Electronic key
Bistable relay

Elevator control
Traffic light

Running LED

Just for fun I designed and tested two running LED circuits based on CD4017. The first one drives a strip of six LED, while the second one works for a strip of eight LED. Both circuits work in bidirectional running.

About the CD4017
The CD4017 can drive a sequence of 10 outputs by activating them one at a time. An output at the low level supplies a negative signal, while an activated output supplies a positive signal. The pin 14 is the clock input. It is often connected to the output of a 555 in astable configuration.
Once the circuit is supplied the CD4017 activates the first output. If the input pins 15 and 13 are supplied by a negative signal, each clock pulse lets the outputs condition change. If the signal to the pin 15 gets positive the integrated circuit resets the outputs condition. The pin 13 is used to break the count with no reset.

Six LED version
On this circuit the LED take the inverted output signals. In other words we’ll see a dark light running back and forth. The outputs 0, 1, 2, 3, 4, 5 turn off the LED from 1 to 6. The other outputs turn off the LED from 5 to 2. So each extreme LED is controlled by a single output, then we only have to use a PNP transistor.
For the middle stages the matter is a bit different, since each LED is controlled by two outputs and turns off when one of them is activated: in that condition the central pin of the transistor is shorted by the low resistor (470) connected to that output. Since the pins 15 and 13 are not used, they are connected to the negative pole of the battery. The running speed can be setted by a trimmer.

Watch on Youtube


Pdf schematic

Eight LED version
On this circuit the LED take the direct output signals. Both clock pins take the signal from the 555 output. Once the circuit is supplied the last output of IC1 sends the positive signal to the clock enable (pin 13) of IC2. So IC1 switches the LED from L1 to L8, while IC2 keeps on the first output. Once the last output of IC1 switches on the clock enable signals are inverted. So IC2 drives the LED from L8 to L1, while IC1 keeps on the last output. The reset input (pin 15) of both integrated circuits takes the positive signal from the last output of IC2.

Watch on Youtube


Pdf schematic