# need to detect the AC load

#### swa8788

Joined Dec 3, 2017
4

In above circuit diagram i am trying to control the 230volt lamp through MCU.
the exact operation will be as given below.

1. When the Switch is ON the MCU won't be able to control the LOAD.
2. When the Switch is OFF MCU controls the LOAD.

Now initially I have to detect whether the load is connected or not, through MCU.
Using below options i can do the same

1.Hall sensor
2.CT

But issue with above two options is the cost. Both of them are too expensive.
Also i can access LINE wire only.
I am thinking to use opto-coupler or shunt resistor(with differential amplifier) in the black box as shown in schematic.

but don't know how to use it.

Joined Jan 15, 2015
5,781
What is the current of your AC Load? A simple easy and non intrusive method is to get one of these. This is just a single example as similar units are manufactured by other manufacturers. You can fabricate your own opto coupler. The sensitivity Turn-on Point: 0.75 Aac RMS can easily be halved by looping the primary wire through twice. The average US cost is under $12.00 USD. About a simple as it gets. Ron #### neonstrobe Joined May 15, 2009 132 You might have a catch-22 problem. If the MCU turns on the lamp there might not be any voltage to provide its power. It would work if the MCU only has to turn the light on, if the "black box" latched. Most SMPS operate from ~85-240V but if the MCU had to work the lamp on or off then it would need something to power it, i.e. some voltage between the lamp and the 240v line. As it is the MCU would work if the lamp is present because the SMPS would power it through the lamp. #### philba Joined Aug 17, 2017 960 Add an AC optocoupler across the manual switch. See the picture. When the switch is open, it develops a voltage across the LED and a logic low on the isolated side. When the switch is closed, it will not develop a voltage and thus a logic high (via a pullup resistor) on the isolated side. You will need appropriate current limiting resistor on the AC side and a pullup resistor on the logic side (may be built into your microcontroller). Maybe$1 of cost.

As neonstrobe mentioned, your diagram as drawn won't work. But I suspect it is incorrect and the power supply has a separate return (i.e. not going through the "black box").

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#### swa8788

Joined Dec 3, 2017
4
What is the current of your AC Load? A simple easy and non intrusive method is to get one of these. This is just a single example as similar units are manufactured by other manufacturers. You can fabricate your own opto coupler. The sensitivity Turn-on Point: 0.75 Aac RMS can easily be halved by looping the primary wire through twice. The average US cost is under $12.00 USD. About a simple as it gets. Ron The AC current is ranging from 10mA to 5 Amps. i am going to design a system with 300nos. of device control through MCU. the sensor cost has to as minimum as possible. I think a shunt resistor with differential amplifier can work. Thread Starter #### swa8788 Joined Dec 3, 2017 4 You might have a catch-22 problem. If the MCU turns on the lamp there might not be any voltage to provide its power. It would work if the MCU only has to turn the light on, if the "black box" latched. Most SMPS operate from ~85-240V but if the MCU had to work the lamp on or off then it would need something to power it, i.e. some voltage between the lamp and the 240v line. As it is the MCU would work if the lamp is present because the SMPS would power it through the lamp. the lamp is nothing but any AC load which operates on 230Vac(ranging from 10mA-5Amps) and the load is get operated through 5Volts relay by MCU Thread Starter #### swa8788 Joined Dec 3, 2017 4 Add an AC optocoupler across the manual switch. See the picture. When the switch is open, it develops a voltage across the LED and a logic low on the isolated side. When the switch is closed, it will not develop a voltage and thus a logic high (via a pullup resistor) on the isolated side. You will need appropriate current limiting resistor on the AC side and a pullup resistor on the logic side (may be built into your microcontroller). Maybe$1 of cost.

As neonstrobe mentioned, your diagram as drawn won't work. But I suspect it is incorrect and the power supply has a separate return (i.e. not going through the "black box").View attachment 140762
well lets consider the switch is closed.
and i want to detect if the load is connected or not.
so i need to connect something is series with the load. like shunt resistor and the voltage drop across shunt resistor can be detected with differential amplifier.
will that work???
or suggest me the AC opto-coupler part number.

#### philba

Joined Aug 17, 2017
960
Is your desire to control the load via MCU and have "local control" (ie, at the physical switch) or is detecting the load a key part of your project? There are several shunt products that can detect various currents that aren't expensive. Look at the schematics of these sparkfun products to figure out what they've done

#### strantor

Joined Oct 3, 2010
5,468