Signals
Digital input: <in>
Digital output: <out>
Description
The NOT symbol, also known as an inverter, simply inverts the level of the input signal. That is, whenever the input is high the output will go low and vice-versa.
The NOT symbol can be expressed using a truth table, where low stands for logical 0 (false), and high stands for logical 1 (true). Thus the truth table shows <out> always to be the complement of <in>.
Truth table for NOT:
|
<in> |
<out> |
|
low |
high |
|
high |
low |
Example: Automatic Camera Control
Sometimes a device provides the opposite signal than you want. For example, say your control system is set up to receive contact closures from an automatic microphone mixer, indicating which microphone has just been spoken into. In a video conferencing application, these closures might be used to point the camera directly at the speaker. However, suppose that instead of supplying a closure each time a microphone was spoken into, the relays were normally all closed and that it supplied an open contact to signify a microphone trigger. You could pass each incoming signal into a NOT symbol to first invert its level. The output signals could then be used to trigger camera presets somewhere else in your logic.
See also Multiple NOT