The wired logic is the way to implement logical decisions using real contacts and switches.
A computer is nothing but billions of microscopic switches (transistors) connecting and disconnecting at dizzying speeds. But before chips existed, engineers were already building mechanical “computers” using relays and large switches.
At its core, the idea is the same: making the circuit make decisions by itself depending on how its contacts are connected.
1. The Bit: Open or Closed
In digital electricity, there are only two states. There is no “half-on.”
- 0 (False/Low): Open Circuit. No current flows.
- 1 (True/High): Closed Circuit. Current flows.
By combining these zeros and ones, we can create complex conditions.
2. AND Logic
We want a machine to turn ON ONLY if two conditions are met at the same time.
Example: A hydraulic press. For it to lower, the operator must press the left button AND the right button (this ensures their hand is not underneath).
The Electrical Solution: SERIES CONNECTION.
We place the switches one after another on the same phase line.
- If you close A → Current stops at B. (Result: 0)
- If you close B → Current does not flow through A. (Result: 0)
- If you close A AND B → The circuit is completed. (Result: 1)
Rule: In Series, if one fails, everything fails.
3. OR Logic: The Convenience
We want a light to turn on if any of the available switches is activated.
The interior light of a car. It should turn on if you open the driver’s door OR if you open the passenger’s door.
The Electrical Solution: PARALLEL CONNECTION.
We place the switches on separate branches, joining their inputs and their outputs.
- If you close A → Current flows through the top branch. (Result: 1)
- If you close B → Current flows through the bottom branch. (Result: 1)
- If you close none → Darkness. (Result: 0)
Rule: In Parallel, it’s enough for one to work for everything to work.
NOT Logic
We want something to turn off when we press a button. Or for an alarm to sound when a window is closed (magnetic sensor).
It seems counterintuitive: we normally associate “pressing” with “turning on.”
The Electrical Solution: THE NORMALLY CLOSED (NC) CONTACT.
So far, we have used “Normally Open” (NO) switches: if you don’t touch them, no current flows. There are switches that work the opposite way: they have a spring that keeps them connected (closed), and when you press them, you separate them.
- Rest State (Not Touched): Current flows → Light ON (1).
- Active State (Pressed): You break the current → Light OFF (0).
This function inverts the logic.
- Input 0 → Output 1.
- Input 1 → Output 0.
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