Lights and Display Board Circuits

Light switch for motorcycles

Many motorcycles have the facility that as soon as the ignition is switched on, their dipped head-lights (or day. running lights) come on. Although on most modern machines these lights go off briefly while the engine is started (so as to prevent a heavy load on the battery), there are some on which this is not so. This shortcoming may be remedied by the circuit described here.

Light switch for motorcycles Schematic diagram

The circuit is based on optoisolator IC1, which detects whether the ‘N(eutral)’light, La1 on the dashboard is on. As long as this light is on, the machine is not in gear. When the engine is started (with the gearbox still in ‘N’), La1 remains on so that the LED in the optoisolator lights. This switches on the transistor in IC1. The gate of the thyristor is then at cart h Potential and I he relay remains deenergized. Headlights LA2 and La3 are off and the engine can be started without these lights coming on. When a gear is selected, La1 goes out and the transistor in IC1 switches off. The thyristor then gets a gate current via R2 and R3, whereupon Re1 is energized. The headings then come on and the machine can be driven away safely. The thyristor remains on as long as the battery is being charged, so that when “N” is selected, for instance, at traffic lights the lights remain on.

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