74LS00 NAND Gate and LED on a Breadboard
A first breadboard circuit, wired the way it would be on a real bench: a 74LS00 powered from +5 V and ground, two switches on one gate's inputs, the unused inputs tied to ground, and an LED lit from the low side through a 470 Ω resistor.
Try it live
This is the Breadboard Simulator itself, running in the page — it is LogicsBench's own example design, read-only. Open it full size, and sign in to make your own copy to change.
- Throw both switches up: the LED lights.
- Hover over a pin to see its voltage, and read the current written beside the resistor.
NAND gate and LED truth table
| A | B | NAND out | LED |
|---|---|---|---|
| 0 | 0 | 1 | off |
| 0 | 1 | 1 | off |
| 1 | 0 | 1 | off |
| 1 | 1 | 0 | lit |
How it works
NAND out = (A · B)′LED lit when NAND out = 0, so it shows A · B
The LED runs from +5 V, through the resistor, into the gate's output. It lights when the output is 0 — a TTL output sinks current far better than it sources it.
So the LED shows the opposite of the NAND: it lights only when both switches are up. That is A AND B, from a NAND gate.
Pin 14 to +5 V and pin 7 to ground power the chip; unused inputs go to ground so they cannot float and draw stray current.
Building it from 74-series chips
| 74LS00 | one NAND gate; pin 14 is VCC, pin 7 ground |
| 470 Ω resistor | limits the LED to about 6 mA |