Flip-Flops

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 IC_3a, 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 IC_3a is the clock pulse (CLK) to Pin 3. Pins 5 and 6 (first flip-flop) alternately switch from 5V (V_CC) 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 V_CC to 0 volts, Q₁ through Q₄ are turned "on" sequentially through the base resistors R₂ through R₅, placing V_CC across each lamp in turn.