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# Boolean Logic Circuits

The sequence of movements of pneumatic cylinders, for example, in practice often requires the logical processing of signals from several operating controls. The most important of these logical functions are AND and OR functions.

ANDing Signals

ANDing two signals results in a logical 1 when both the 1st AND the 2nd input signals are both themselves 1. The following interactive animation shows a circuit in which the indicator lamp P only lights when both switch S1 AND S2 (the flow of current is shown in red) are closed. Check out how the circuit works, by activating the switches in various combinations. It can be seen that the Boolean AND function corresponds to a circuit with both switches in series.

ORing Signals

ORing two signals results in a logical 1 when either the 1st OR the 2nd input signals (or both) is 1. The following interactive animation shows a circuit in which the indicator lamp P only lights when either switch S1 OR S2 (the flow of current is shown in red)  are closed. Once again, check out how the circuit works. You can see that the Boolean OR function corresponds to a circuit with both switches in parallel.

Combining more than Two Signals

ANDing and ORing more than two signals functions in the same way as above. The following animation shows an AND gate with up to five inputs using logic diagram symbology. Check the functioning of the gate by selecting the number of inputs ("Inputs" box) and selecting various combinations of 1s and 0s at the inputs.

The following animation shows a corresponding OR gate. Once again, check out how this works with more than one input.