NAND gate S-R flip-flop
- 4011 quad NAND gate (Radio Shack catalog # 276-2411)
- 4001 quad NOR gate (Radio Shack catalog # 276-2401)
- Eight-position DIP switch (Radio Shack catalog # 275-1301)
- Ten-segment bargraph LED (Radio Shack catalog # 276-081)
- One 6 volt battery
- Three 10 kΩ resistors
- Two 470 Ω resistors
Caution! The 4011 IC is CMOS, and therefore sensitive to static electricity!
Although the parts list calls for a ten-segment LED unit, the illustration shows two individual LEDs being used instead. This is due to lack of room on my breadboard to mount the switch assembly, two integrated circuits, and the bargraph. If you have room on your breadboard, feel free to use the bargraph as called for in the parts list, and as shown in prior latch circuits.
- The difference between a gated latch and a flip-flop
- How to build a “pulse detector” circuit
- Learn the effects of switch contact “bounce” on digital circuits
The only difference between a gated (or enabled) latch and a flip-flop is that a flip-flop is enabled only on the rising or falling edge of a “clock” signal, rather than for the entire duration of a “high” enable signal. Converting an enabled latch into a flip-flop simply requires that a “pulse detector” circuit be added to the Enable input, so that the edge of a clock pulse generates a brief “high” Enable pulse:
The single NOR gate and three inverter gates create this effect by exploiting the propagation delay time of multiple, cascaded gates. In this experiment, I use three NOR gates with paralleled inputs to create three inverters, thus using all four NOR gates of a 4001 integrated circuit: