# Lightbulb moment: learning logic gates with switches

I introduced logic gates to year 9 again this year. Last year we did the theory, filled in truth tables and then I got them to built half and full adders in logic.ly – which was fine, they really got into it.

This year though I took a different tack. Inspired by reading Code by Charles Petzold, I decided to introduce the theory of the AND, OR and NOT gates but back this up with some physical creation of the first two of these gates.

I borrowed some modular electronics from the DT department to build first an AND gate. All you need is a power supply, two switches in series and a lightbulb. I got the girls to wire this up from a circuit diagram on the board:

I then let them discover that we could only light the bulb if the first AND second switches are both turned on.

We used this to fill in our truth tables, then I got them to rewire the circuits with the switches in parallel.

This is, of course, now an OR gate as it lights the bulb if the first OR the second switch is turned on:

I didn’t have enough of these circuits, alas, for everyone to have a go, but there were a few (ahem) lightbulb moments that might not have occurred without the physical realisation of quite an abstract concept. Ideally I’d have a big bucket of switches, wires, lightbulbs and power supplies and my class could all build them themselves.

Update:
These modular electronics kits are called Economatics and were made by Omega Electronics. Unfortunately they don’t seem to be made any more – does anyone know of anything similar you can buy today? Needs to be VERY simple: switches, lightbulbs, wires – possibly relays but nothing more.

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### 2 Responses to Lightbulb moment: learning logic gates with switches

1. James says:

That’s a great practical illustration. I only ever gained a superficial understanding of logic gates which were always presented as closed black boxes. I’m sure some practical demos like this would have helped a lot.

• blogmywiki says:

Thanks James – really annoying these kits don’t seem to be made any more! They are great.