ROCKET_LAUNCHER_IGNITER_CIRCUIT

Published:2009/7/13 21:43:00 Author:May | From:SeekIC

An ISD1000A chip (IC1) containing a previously recorded message is connected in a simple playback-only circuit that operates when power is supplied by closing the START switch (S1). A 7805 voltage regulator, IC3, is used to drop the 12-V input voltage to 5 V. When the audio message is completed, IC1 produces a 16-ms low output pulse at pin 25. That low output pulse is fed to the input, pin 5, of a monostable multivibrator, IC2. That IC produces a long timed output pulse at pin 6, which turns Q1 on, supplying power to the igniter and firing the rocket engine. This circuit contains several safety features. Switch S2 removes power from the igniter fuse. One gate of a 4011 quad twoinput NAND gate (IC4-a) keeps the 4528B monostable multivibrator from misfiring and igniting the rocket motor prematurely. When the Start switch is first activated, IC4-a's input goes high while C4 is charging up, and its output at pin 3 goes low, keeping IC2 from responding to any false input pulse at pin 5. IC4-a's pin 3 clamps the input of Q1 to ground, through Dl, keeping it turned off. After a few seconds, C4 is fully charged and IC4-a's output goes positive, enabling IC2 and allowing Q1 to operate. Though not shown in the figure, the inputs of the quad IC's three unused gates (IC4-b to IC4-d, pins 5, 6, 8, 9, 12, and 13) must be tied to ground.



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