3rd Generation computers used integrated circuits.
Logic gates are built as integrated circuits (also referred to as chips, or microchips). An integrated circuit is a set of electronic circuits on one small flat piece (or “chip”) of semiconductor material, normally silicon. The integration of large numbers of tiny transistors into a small chip results in circuits that are smaller, cheaper, and faster than those constructed of discrete electronic components.
Each circuit has a code printed on them which is used to identify the circuit. (e.g. See List of 7400 series integrated circuits on https://en.wikipedia.org/wiki/List_of_7400_series_integrated_circuits)
Each circuit is different and you need to know how the circuit is wired internally to use it in your own circuits (to indentify the purpose of each pin). See image below as an example of integrated circuit 7408 which consists of four AND gates.
Integrated Circuit 7408: Quad 2-input AND gate
Your Challenge
For this challenge, we will assume that you have some integrated circuits (ICs) but do not know which logic gates they consist of. Instead of looking up for their code on the Internet, you will create an electronic circuit and use this circuit to test how your IC behaves. Your circuit will have:
- Two inputs: the yellow and a blue button on the diagram below.
- One output: the green LED on the diagram below.
By using the buttons and writing down the outputs, you will be able to draw the truth table of this logic gate and hence identify which logic gate is used in this IC.
| Input A | Input B | Output |
| 0 | 0 | |
| 0 | 1 | |
| 1 | 0 | |
| 1 | 1 |
Check this blog post to investigate the truth tables for some of the key logic gates.
Logic Gates circuits available on: kitronik.co.uk.
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