The discussed LED lamp chaser circuit can be effectively used for indicating or warning road diversions or when a roadwork is in progress, especially in areas where street lamps are absent and in accident prone dark roadways.
Roadworks and highways are usually marked during the hours of darkness by yellow flashing lights. These may often be linked together to form a ‘running’ flashing light.
Road diversions and the like are then clearly visible. The road diversion warning indicator circuit using running LED lights 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 lC used, this frequency will be of the order of 6 Hz 1 30% when potentiometer Pl is in mid position. The output of the clock generator is fed to the Johnson counter lC1L The outputs of this counter become logic 1 in sequence.
The counter is reset to the start when Q4 goes to logic 1. This explains the link between pins 15and 1001‘ lC1.0utputs Q0. . . Q3 are connected to four monostable multivibrator circuits consisting of N2 . . . N5.
The multivibrators are triggered by the negative going edge of the square wave outputs of Q0 . . . Q3 and the pulse period 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 current for the LE Ds 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 consumption 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 all terminals are located at one edge. The four groups of LEDs are connected to pins A . . . D which are clearly marked on the circuit diagram and the board.
Parts list for the proposed road diversion warning indicator circuit using running LED lights
P1 . . . P5 = 1 M preset potentiometer
' T1 ...T4=BC547B
D1 . . . D16 = LED yellow