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Simple
LED
Flasher
(Grade
Crossing) |
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Led
Pilot
Light
(
Constant
Current
Regulated) |
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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. |
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LED
Traffic
Light
Circuit
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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).
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