The LED traffic Light circuit controls 6 LEDs (red, yellow and green) for both north/south directions and east/west directions. The timing sequence is generated using a CMOS 4017 decade counter and a 555 timer. Counter outputs 1 through 4 are wire ORed using 4 diodes so that the (Red – North/South) and (Green – East/West) LEDs will be on during the first four counts. The fifth count (pin 10) illuminates (Yellow – East/West) and (Red – North/South). Counts 6 through 9 are also wire ORed using diodes to control (Red – East/West) and (Green – North/South). Count 10 (pin 11) controls (Red – East/West) and (Yellow – North/South). The time period for the red and green lamps will be 4 times longer than for the yellow and the complete cycle time can be adjusted with the 47K resistor. The eight 1N914 diodes could be subsituted with a dual 4 input OR gate (CD4072).
Copyright 1999 Bill Bowden