Technologies K–10 · Years 9–10
Logic gates from switches: AND, OR, NOT and the two-way light
Computing Technology 7–10 (NSW, 2022); Digital Technologies: Processes and production skills, Generating and designing (ACARA v9)
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The idea
Switches in series behave as AND, switches in parallel as OR, a push-to-break switch as NOT, and two two-way switches as the staircase light, so logical operators in algorithms have physical circuits behind them.
What you need
- 2 AA cells (3.0 V) in a holder, 1 red LED (1.9 V typical), 1 × 220 Ω resistor
- 2 push-to-make switches, 1 push-to-break switch, 2 two-way (SPDT) switches
- Breadboard and jumper wires
- BBC micro:bit and the MakeCode editor
How to do it
- Build AND: two push-to-make switches in series with the resistor and LED. Test all four combinations and record a truth table.
- Build OR: the two switches in parallel. Test and record.
- Build NOT: the push-to-break switch in series. Test and record.
- Build the staircase circuit with the two two-way switches. Test and record.
- Program the micro:bit to show a tick when buttons A and B are both pressed, then change it to 'or' and 'not'; compare with the circuit tables.
- Design a flowchart and circuit for a shed alarm that sounds when the door is open and the alarm is armed.
What you should see
AND lights the LED only when both switches are pressed (truth table 0 0 → 0, 0 1 → 0, 1 0 → 0, 1 1 → 1). OR lights it when either or both are pressed (0, 1, 1, 1). NOT lights it until the switch is pressed. The staircase circuit lights the LED when the two switches are in matching positions (1, 0, 0, 1), the XNOR function. The LED current is (3.0 − 1.9) ÷ 220 = 5.0 mA in every case. The micro:bit tables match the circuit tables row for row. The learner knows it worked when each circuit's table matches its Boolean expression.
What changes
This activity lists no variables to change, measure and keep the same.
Common misconceptions
Each of these ideas is wrong, and the activity is a chance to test it.
- Logic gates are only software (they began as circuits and still are, in transistors).
- OR means one or the other but not both (OR is true when both are true).
- Series and parallel give the same result because both use two switches (series needs both; parallel needs either).
Safety card
Hazards
- Short circuit across the cells
Controls
- Keep the resistor in every path; never join cell terminals directly
Note
Low-voltage cells only. No chemicals or heat.
Curriculum references
The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.
- Computing Technology 7–10 Syllabus (2022), NESA. Current elective syllabus. Code read from the outcomes page on 2026-09-22.CT5-THI-01CT5-OPL-01
- Australian Curriculum v9AC9TDI10P05
Sources
The pages the author read to write this activity.