Search Light Signal


Posted on Feb 5, 2014

This circuit controls a Searchlight type signal head and produces solid - RED, YELLOW or GREEN indications. The signals can be connected for NORMAL or APPROACH type lighting of the Green signal. The circuit uses a LM556 - Dual Timer IC in a complimentary output configuration to drive a red and green, bipolar type light emitting diode to produce t


Search Light Signal
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he signal`s three colours. There are two complete block signal circuits on the PCB in the photo. The circuit on the left side is wired for APROACH lighting of the Green signal while the circuit on the right side is wired for NORMAL lighting of the Green signal. Schematics for both configurations are shown below. APPROACH - Type Lighting means that the GREEN signal is on only when the block after a particular signal is showing a RED signal. The Green signal is on when Terminal GI is LOW. The YELLOW or RED input functions are the same as for Normal GREEN lighting. The next diagram shows five signal block circuits connected using the terminal blocks mounted on the circuit boards. A four conductor cable could be used to connect the individual blocks together. The signal circuits can be controlled by any device that can pass at least 1 milliamp current and shares a common connection with minus terminal of the signal circuit`s power supply. The circuit is designed for a 12 volt power supply voltage and will drive light emitting diodes at approximately 10 milliamps. Other supply voltages and LED currents can be used by changing the values of certain resistors in the circuit. - If the signal LEDs are too bright, external resistor can be connected at the circuit board`s outputs rather than replacing resistors R5 on the circuit board. The combined current from a DETECT INPUT of one block and the YELLOW INPUT from the previous block...




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