What does it do?
| Turns something off when both inputs are activated. |
 |
How does it operate?
|
NAND Gate Circuit
Click on the circuit diagram to download a Livewire file of the circuit that you can investigate and add to your own circuit. |
When two input signals are used with a NAND gate, the NAND gate subsystem provides an output signal that is low when both input signals are high. Otherwise, the output signal is high.
The output signal from the NAND gate is shown in the truth table below, with 0 meaning “low” and 1 meaning “high”.
Truth table for a 2-input NAND Gate
|
|
American (ANSI) Symbol
 |
European (DIN) Symbol
 |
|
The simplest NAND gate ICs (such as the 4011B) have two input signals. Other NAND gate ICs are available with more inputs. The 4023B CMOS IC has three input signals, the 4012B has four input signals and the 4068B has eight input signals. In all NAND gates the output signal goes low when all the input signals are high.
It is possible to combine NAND gates to produce an AND gate. NAND gates can also be made to work like inverters. |
Possible applications
- Turning an output device off when two sensors are both activated
Making
|
Pins of 4011B
|
How part of the PCB might look |
The PCB shows the basic circuit. Several gates in the IC are not used in this simple design; they can be applied in other subsystems. Any unused input pins should be connected to 0V or Vs, to prevent damage by static electricity.
In the example PCB, the two input signals go to pins 1 and 2, and the output signal comes from pin 3. Any of the other three NAND gates in the IC could be used.
Build and test the units that will provide the input signals before adding the NAND gate IC.
Use a Dual In Line (DIL) socket for the IC. Before inserting the IC, connect the power supply and use a voltmeter to check that:
- the voltage on pin 7 is low (0V);
- the voltage on pin 14 is high (the supply voltage);
- the voltage on pins 1 and 2 (the blue PCB tracks) goes high and low in response to the units that provide the input signals.
Insert the IC the right way round.
Testing
Make sure that the signal going out (on the green PCB track) follows the NAND gate truth table.
Fault finding
If there is a fault, check that:
- The voltage on pin 7 is low (0V)
- The voltage on pin 14 is high (the supply voltage)
If there is a fault, check the tracks and solder joints.
Alternatives
- PICs – more flexible but more expensive.
Web links
Return to list of datasheets
