Build 008Queued

Let one circuit switch another

Use a relay to control a second circuit. Inside it, a small electromagnet moves a switch.

Blueprint illustration of two low-voltage circuits connected through a clear relay

Before we start

Can one electric circuit turn another circuit on without the two paths touching each other?

The goal

Understand a relay as an electromagnet and a switch working together.

How we'll do it

  1. 01Find the relay's coil connections and its switching connections.
  2. 02Use the button and first battery to power only the coil.
  3. 03Build a separate LED circuit through the relay contacts.
  4. 04Press the button, listen for the click, and trace which path changed.

Optional equipment

Prints that make the build easier. None are required. Every build works with tape and clips.

Instructables

Telegraph key and sounder

The sounder is a relay we can watch working: a coil, a lever, a click.

Not printed yet

Printables

Snaptronics circuit bricks

Two separate loops are easier to see when each part is its own brick.

Careful: Ball magnets are dangerous if swallowed. Grown-up assembly only.

Not printed yet

Read alongside

Family read

Wired

Anastasia Suen and Paul Carrick

Follows electricity from the generator to the switches in a home.

Bench guide

Make: Electronics — Learning by Discovery

Charles Platt

Moves from ordinary switches to a relay, where one circuit controls another.

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