What does it do?
| Makes something happen when either, but not both, inputs are activated. |
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How does it operate?
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Exclusive OR 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. |
The exclusive-OR gate (XOR) subsystem provides an output signal that is low if either both input signals are high or both input signals are low. Otherwise, the output signal is high.
The output from the Exclusive OR gate is shown in the truth table below, with 0 meaning “low” and 1 meaning “high”.
Truth table for an Exclusive OR gate
The 4070B CMOS IC contains four Exclusive OR gates. |
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American (ANSI) Symbol
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European (DIN) Symbol
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Possible applications
- Turning an output device on when only one out of two sensors is activated
Making
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Pins of 4070B
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How part of the PCB might look
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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 Exclusive OR gates in the IC could be used.
Build and test the units that will provide the input signals before adding the Exclusive OR 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 voltages 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 Exclusive OR 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
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