Electronic – How to design an AC current detection switch

achall-effecthome-automationmicrocontrollersensor

I am working on a home automation system and I need to detect if an appliance is getting power or not.

I need a AC current detection switch which can be mounted on a power line and send a DC voltage signal as output to a micro-controller whenever it detects an AC current in the line.

I did some searching and found Hall effect sensors which provided detection with isolation but since the magnetic field will fluctuate so will the output. I need a Hall effect sensor which just gives a DC voltage when it detects a magnetic field from an AC current line and gives a DC output which could be fed to a comparator.

I am a newbie in electronics and work on DIY projects.

I have planned to design my own board to keep the cost low.

Appliances work on 230 VAC and 5 A max current.

Best Answer

schematic

simulate this circuit – Schematic created using CircuitLab

Figure 1. Simple diode-drop current sensor with opto-isolator.

  • The diodes drop a maximum of about 2.1 to 3 volts depending on current.
  • OPTO1 is a bi-directional LED opto-isolator. These have infra-red LEDs internally and so forward voltage drop is about 1.2 V. R1 will limit the current to 10 mA.
  • The diodes need to be rated for the maximum current (including any switch-on surge) will dissipate about 0.8 x I watts each. They don't need to be high voltage because there is a maximum of 3 V across this part of the circuit.
  • C1 will hold the voltage between pulses from the opto-isolator and simplify the micro code.