A Leap Into Logic - Switch Logic

The Logic Gate Symbols (ENOR = XNOR; EOR = XOR)

Did you realize that logic can be represented by a set of switches? After all, transistors are switches that create the chips we call TTL chips (Transistor-transistor logic). Better and simpler than any TTL, logic in the form of switches in combonation can be used for all the gates you have came to love: AND, OR, NOT (AOI) and even NAND, NOR, XOR, XNOR.

If you unfimiliar with these expressions that let me quickly bring you up to speed:
AND, OR, NOT, NAND, NOR, XOR, XNOR are all logic gates.

AOI Logic

AOI Logic is logic represented with only and, or, and invertor (previously called not) logic gates.

AND example: If, mom is sleeping and dad is downstairs, then, I can go sneak some cookies.
Condition: Mom sleeping and dad being downstairs
Result of condition being met : You can get some cookies.

OR example: If he or she goes to the bathroom, someone must be notified.
Condition: EITHER he goes to the bathroom OR she goes to the bathroom
Result: Someone must be notified

An invertor gate is like using "NOT" in a sentence:
Not Example: If he goes, I would not go.
Condition: If he goes
Result: I would not go

NOR and NAND

the N precceeding "NOR" and "NAND" means to take the opposite (inverted value) of the outcome of the "OR" or "AND" gate.

A nor B = A or B > NOT > Answer = opposite of the result from A or B.
A nand B = A and B > NOT > Answer = opposite of the result from A and B.


Switches are like our heads. We can shake "YES" or "NO" which is like "ON" or "OFF".

A simple switch that can be on and off like a light switch serves the basic logic function of true or false.

AOI Logic by Means of Switches

Switches in series operate as an AND gate

Creating an AND Gate with Switches
To create an AND gate with switches you need two (2) switches in series (series means one path for the electricity to flow). This is because if either switch is OFF than the whole circuit is OFF and only when both switches are on (true) will electricity flow through the circuit.

A Schematic AND-Gate Example

Creating an OR Gate with Switches

Switches in parallel acting as an OR gate

To create an OR gate with switches you need two (2) switches in parallel (parallel means 2 lines for electricity to flow, across either switch). This is because if either switch is ON there is a complete path for electric current (electricity) to flow. So if switch 'A' or switch 'B' is on then your circuit will be complete and flowing.












Creating an NOT Gate with Switches
To create an NOT gate all you need is a switch that can shorten the flow of electricites path, so the logic path has a negative or false value and the electricity carries its positive charge through the shortest path to the negative terminal of the battery or cell.



More Online Logic Resources:
http://www.kpsec.freeuk.com/gates.htm