Background reading · Technology

Input, process, output: seeing the system

How to break any smart device into what it senses, what it decides and what it does, and why engineers draw system diagrams.

Walk into a supermarket and the doors slide open. You did not touch anything. Something noticed you, something decided to open, and something moved the doors. That is a system, and almost every smart device works the same way.

Three boxes

Input: the part that senses something, like a button, a light sensor, a thermometer or a motion detector. - Process: the part that decides what to do, usually a small computer chip called a microcontroller running a program. - Output: the part that does something, like a light, a buzzer, a screen or a motor.

Engineers draw this as three boxes joined by arrows. It is called a system diagram. It does not show every wire. It shows what flows through the system: signals, energy or information.

Systems inside systems

Big systems are made of smaller ones called subsystems. A car has a braking subsystem, a steering subsystem and an entertainment subsystem. Your trap alert might have a power subsystem (the batteries), a sensing subsystem (the switch), a decision subsystem (the code) and an alert subsystem (the radio and the screen). Breaking a problem into subsystems means you can build and test one part at a time.

Feedback: systems that check themselves

A heat pump does not just blast warm air forever. It measures the room temperature, compares it with the setting, and turns down when the room is warm enough. When the output changes the next input, that is called a feedback loop. Feedback is what makes a system 'smart'.

A Waikato system that went global

It began with a horse. Waikato farmer Bill Gallagher and his brother were fixing a motorbike when a horse kept rubbing against their car, so Bill rigged the car to give it a small shock. Around 1937 he turned the idea into an electric fence, a cheap way to control farm animals. As a system, the input is power, the process is an energiser that sends short pulses along the wire, and the output is a sharp but safe shock when an animal touches it. His fences grew from a Hamilton backyard workshop into products used in more than 100 countries.

Try it

Pick something at school that switches on by itself, like a hand dryer or an automatic tap. Draw its system diagram. Where is the feedback, if there is any?

Sources and further reading

Written for Kōkiri Learn students in our own words. Check facts against the sources.

Used in: Smart Circuits: Electronics and Control