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MODEL_FIRE_ENGINE_FLASHER_CIRCUIT

2017-02-03 21:48  
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MODEL_FIRE_ENGINE_FLASHER_CIRCUIT
This circuit was designed to add both a blue flashing light sequence and a two-tone siren effect to a model fire engine. IC1 is a quad NAND Schmitt trigger, and IC1a provides a low-frequency waveform, which is inverted by IC1b. Complementary outputs are obtained, which drive transistors TR1 and TR2. These driver transistors operate D1 and D2, which are two blueLEDs. The model had a blue translucent molding on its roof and yielded a surprisingly realistic effect. The outputs fromIC1a and IC1b are also used to control gated astables IC1c and IC1d, which are set to oscillate at different frequencies to simulate a typical British two-tone siren, sounded by WD1, a piezo disk. Battery B1 should be an alkaline or rechargeable9-V type because the current consumption is relatively high. S1 was a slide switch fitted on the rear of the vehicle.The sounder is optional.