What does it do?
|Makes something happen when both inputs are activated.
How does it operate?
AND 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.
For an AND gate with two input signals (Input A and Input B), the Output signal goes high if both input signals are high.
The output from the AND gate is shown in the truth table below, with 0 meaning “low” and 1 meaning “high”
Truth table for a 2-input AND gate
American (ANSI) Symbol
European (DIN) Symbol
The simplest AND gate ICs (such as the 4081B) hve two input signals. Other AND gate ICs are available with more input signals. The 4073B CMOS IC has three input signals and the 4082B has four input signals. In all AND gates the Output signal goes high when all the Input signals are high.
It is possible to combine NAND gates to produce an AND gate
- Turning an output device on when two sensors are both activated
- Making something flash or beep when a sensor is high
Pins of 4081B
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 AND gates in the IC could be used.
Build and test the units that will provide the input signals before adding the AND 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.
Make sure that the signal going out (on the green PCB track) follows the AND gate truth table.
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.
- PICs - more flexible but more expensive
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