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4 Stage Sequencer

4 Stage Sequencer

The major components of the lamp sequencer consist of three integrated circuits, four transistor switches, four lamps, and associated biasing and timing resistors and capacitors.

In operation, the astable multivibrator consisting of IC3a, R1 and C1 is an oscillator whose frequency is determined by the R1 and C1. Integrated Circuit 1 (IC1) is a dual D-type positive edge triggered flip-flop (type 74HC74). The 5-volt switching from IC3a is the clock pulse (CLK) to Pin 3. Pins 5 and 6 (first flip-flop) alternately switch from 5V (VCC) to 0V for each clock pulse, and Pins 8 and 9 (second flip-flop), provide alternate switching from 5V to 0V at half the first flip-flop frequency. These combined outputs then switch IC2 (type 74HC00) positive NAND gate through the four stage sequences (Pins 3, 6, 8 and 11) at the desired rate. As IC2 sequences from VCC to 0 volts, Q1 through Q4 are turned "on" sequentially through the base resistors R2 through R5, placing VCC across each lamp in turn.