Arduino Current Monitor with ACS712 and Relay Loads
Level 47 · How Much Power · 30 minutes
An energy meter: a current sensor shows the amps on a screen, and a relay trips a warning past a safe limit.
Preview the project free; a course seat is required to run and submit. No hardware kit needed.
Your project challenge
Build an energy meter. Wire it up: - Current sensor: VCC 5V, GND GND, OUT A0 - Relay: VCC 5V, GND GND, IN D7 - LCD: the usual twelve wires Show the amps on the top row, to one decimal. Trip the relay at 2.0 A; reset it only below 1.5 A.
Components you’ll use
- Arduino Uno
- ACS712 Current Sensor
- Relay Module
- LCD 16x2 Display
What you’ll build
An energy meter. It shows how many amps an appliance draws, and it trips a red OVERLOAD lamp when the load is too big.
How it works
- The current sensor sits in the appliance’s power line. Its OUT pin gives a voltage.
- At no current, OUT is 2.5 V, half of 5 V. Each amp adds 0.185 V.
- The reading is noisy, so add up 50 readings and divide by 50.
- The relay is active low:
LOWtrips the lamp. It switches the lamp, not the appliance.
The key idea
The zero is in the middle. Take away 2.5 V first, then divide by 0.185.
amps = (volts - 2.5) / 0.185;
Then use two lines: trip at 2.0 A, and reset only below 1.5 A.
⚠ Watch out
Forget the 2.5 V and a switched-off appliance reads 13.5 A. With one line at 2.0 A, a current wobbling around it clicks the relay again and again.
The interactive editor includes the wiring guide, code editor and simulation controls.