Skip to content

Wired Logic: AND and OR

Run the Wired Logic MicroSim Fullscreen

You can include this MicroSim on your own website with this iframe:

1
<iframe src="https://dmccreary.github.io/beginning-electronics/sims/wired-logic-and-or/main.html" height="547px" scrolling="no"></iframe>

About this MicroSim

Long before any chip is involved, a logic gate is just a wiring pattern. Two switches in series make an AND gate: current has one path, so it needs both switches closed. Two switches in parallel make an OR gate: there are two paths, so either one on its own is enough.

Both circuits are on the board at once, and the truth tables beside them fill in live as you flip switches.

The Circuit

AND — series, in the top half:

T+ rail → a5 → SW A → SW B → R1 220Ω → D1 (red) → T− rail

OR — parallel, in the bottom half:

B+ rail → j5 → SW C ┐
                    ├→ R2 220Ω → D2 (green) → B− rail
B+ rail → j5 → SW D ┘

Switches C and D both bridge the same pair of columns, which is what puts them in parallel. On the board you can see it directly: two switches stacked one above the other, spanning the same span of holes.

Component Value Purpose
BAT 5 V supply
A, B latching switches the AND inputs
C, D latching switches the OR inputs
R1, R2 220 Ω current limiting
D1, D2 red, green the two gate outputs

How to Use It

  1. Click a switch on the board, or press 1, 2, 3, 4. The switches latch, so you can set any combination.
  2. Work through all four input combinations on the AND side and watch which row of the truth table highlights.
  3. Do the same on the OR side. Compare the two output columns.

What the Animation Shows

Current only flows on a completed path, so the wires themselves show you which gate is satisfied. With only switch A closed, the current stops at the open B contact and no dots appear past it — the "0" in the truth table is visible on the board as a path that goes nowhere.

Lesson Plan

Grade Level, Subject and Topic

Middle school and high school. Electronics and digital logic. Series and parallel paths as Boolean operations.

Learning Objective

Students will be able to construct the truth table for an AND gate and an OR gate by setting switch combinations on a breadboard and observing which configuration completes a circuit.

Activities

Fill in the table on paper first

Before touching the sim, have students predict all four rows for each gate. Then verify. The OR row 1 1 is the one most often predicted wrong — many students expect two closed switches to somehow be "more on".

Name the pattern

Ask which physical arrangement corresponds to which operation, and why series means AND. The answer — one path, so every switch must be closed — generalizes to three and four inputs.

Extend it

How would you wire a three-input AND? A three-input OR? What arrangement would give you "A and (B or C)"?

Assessment

  • Switch A is closed and B is open. Is any current flowing in the top circuit? Where does it stop?
  • Which gate would you use for a garage door that opens only when a button is pressed and a safety sensor is clear?
  • Draw the switch arrangement for a lamp controlled from either end of a hallway.

Model Limitations

This simulation solves the circuit in DC steady state. It does not model transient behavior, contact bounce, capacitance, inductance or AC. Component values are ideal — no tolerance, no contact resistance, no wire resistance. Real switches bounce for a few milliseconds on closing, which matters in digital circuits and is not shown here.

References