ElectroLab AIVisual build guides
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Beginner+

Relay Timer Controller

Build a timed relay circuit with a protected coil driver, adjustable delay, trigger input, and low-voltage load contacts.

Safety first, always.

ElectroLab AI teaches theory, low-voltage electronics, and planning concepts. Mains voltage, switchboards, fixed wiring, high-current systems, and legal electrical work must only be performed by licensed electricians where required.

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Relay Timer ControllerA trigger starts a timer; a transistor drives the relay coil; the contacts switch a separate low-voltage load.VCCGNDtriggertiming RCoutputcoil -coil +clampNO contactload supplyDC IN5-12 VTRIGGERbutton/sensor555 TIMERdelayDRIVERBJT/MOSFETRELAYcoil + contactsFLYBACKstripe to +DC LOADfan / LEDLow-voltage DC loads only. Do not use this project for mains or fixed wiring.

Switching control build

Build a low-voltage relay timer that can switch small DC loads with a clean trigger and flyback protection.

Bench time

2-4 hours

Typical parts

$18-$45 AUD

Power

5-12 V DC

You finish with

Adjustable timed relay controller

Before the first wire

Know the build before you power it.

Keep the relay load low-voltage DC for this build.

A relay coil is an inductor, so it needs a flyback diode.

Do not switch mains or fixed wiring with this project.

Separate the timing circuit ground from high-current load wiring layout as much as practical.

Bill of materials

7 parts groups to gather

Check every spec

QtyPartExact specWhat it doesInspect before use
1555 timer or delay moduleMonostable/delay outputCreates adjustable timing.Supply voltage matches relay coil/control circuit.
1Relay5 V or 12 V coil, contacts rated for low-voltage loadIsolated switch contact.Identify coil, common, normally open, normally closed.
1NPN transistor or MOSFETRated for relay coil currentDrives coil from timer output.Pinout confirmed.
1Flyback diode1N4148/1N400x or suitableProtects driver from coil kick.Stripe to coil positive.
1Timing pot and capacitorValues chosen for delay rangeSets on-time.Electrolytic polarity correct.
1Trigger switch/sensorPushbutton, reed switch, or logic triggerStarts the timer.Debounce if needed.
1Low-voltage loadLED strip, buzzer, or small fan within relay ratingShows the timed output.Load current below contact rating.

Build boundary

This guide switches low-voltage DC loads only. It does not authorize or describe mains switching, appliance repair, fixed wiring, or safety-critical control systems.

Part modules vary. Read the markings and datasheet for the exact board in front of you before applying power.