Simple LED Flasher (Grade Crossing)

Led Pilot Light ( Constant Current Regulated)

Led Pilot Light
by Tony van Roon

LED's are funny things. They only work at Vdc within specific tolerances, and normally connected with a current limiting resistor to the powersource. Instead of a resistor, you can use a FET (Field Effect Transistor) such as the ECG312, NTE312, try others. The ones mentioned I had available.
When the gate and the source are connected together, it behaves as a current regulator. In the circuit above the current is constant between 6 and 8 mA at 5 to 30Vdc.
If a diode is added (the 1N4148 is optional) this circuit is protected against polarity reversal and can be connected to a AC source of 5 to 20 Vac.

LED Traffic Light  Circuit

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 substituted with a dual 4 input OR gate (CD4072).