How to Make Flashing Running Lights Circuit

Roadworks are usually marked during the hours of darkness by yellow flashing lights. These may often be linked together to form a running’ flashing light.

These are actually running flashing or chasing light circuit. Road diversions and the like are then clearly visible. The circuit described here provides a similar effect but for use in model roadways for instance. The speed of the running’ row of LEDs is determined by the frequency of the clock generator N1. Depending on the type of IC used, this frequency will be of the order of 6 Hz t 30% when potentiometer P1 is in mid position. The output V of the clock generator is fed to the - Johnson counter lC1. The outputs of this counter become logic 1 in sequence. The counter is reset to the start when O4 goes to logic 1. This explains the link between pins 15and 10of lC1.0utputs OO. . . O3 are connected to tour monostable multivibrator circuits consisting of ll2 . . . N5. The multivibrators are triggered by the negative going edge of the square wave outputs of O0 . . . O3 and the pulse period g can be preset with potentiometers P2 . . . P5 which of course determine how long each group of LEDs will light. These periods need to be more or less equal to ensure smooth running of the lights. The circuit uses four groups of four LEDs each. The LEDs in each group will light simultaneously. Figure 2 shows how the LEDs should be connected for road markings in a bend: LEDs D16, D15, D14 and D13 light first,followed by D12, D11, D10 and D9, and so on. Schmitt triggers N2 . . . N5 are not capable of supplying sufficient cur- rent for the LEDs and therefore the buffers T1 . . . T4 are included. The current through the LEDs is about 30 mA during each flash;the average current taken by the circuit operating at the highest frequency is of the order of 30 mA. When, however, the flash period is longer than the running period, the current con- sumption may rise to a `maximum of 100 mA. The printed circuit board (see figure 3) is fairly compact. The preset potentiometers are neatly grouped together and altered on the circuit diagram and the board.



Parts list

Resistors:
R1= 47 k
R2...R5,R10...R13=10k
R6..°.R9=22k
R14...R17=47.Q
P1 . . . P5 = 1 M preset potentiometer
Capacitors:
C1 = 330 n
C2...C5=100n
C6 = 10 p/16 V
Semi-conductors:
‘ T1 ...T4=BC547B
D1 . . . D16 = LED yellow
IC1=4017
lC2=40106