AC load sensing

[swa]

In the attached 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.
U sing below option i can do that.

1.Hall sensor
2.CT

But issue with above two options is the cost. Both of them are too expensive.

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.

Please help.

 

[kellys_eye]

Why would a current transformer be expensive? You can make one from a few dozen turns of wire around a ferrite (or even open-air).

If the load is genuinely a lamp then you could also use a photodetector to determine its status.

 

[AnalogKid]

Now initially I have to detect whether the load is connected or not, through MCU.

First, let's clear up the question. By "connected", do you mean connected to AC power through the switch? If yes, then an optocoupler can give you an AC-isolated square wave signal when the switch is closed, but it cannot tell you if the light has burned out. A light sensor such as a phototransistor or an LDR (cadmium sulphide cell) can tell you both things.

In other words, what do you really want to sense:
a) the switch is closed.
b) the light is on.

ak

 

[swa]

Why would a current transformer be expensive? You can make one from a few dozen turns of wire around a ferrite (or even open-air).

If the load is genuinely a lamp then you could also use a photodetector to determine its status.

____________
I going to use this system to control more than 300 devices at a time.
So detecting a load connected or not with CT will make system costly.

the load can be can be any thing ranging from 5 watts to 1000 watts.

 

[swa]

First, let's clear up the question. By "connected", do you mean connected to AC power through the switch? If yes, then an optocoupler can give you an AC-isolated square wave signal when the switch is closed, but it cannot tell you if the light has burned out. A light sensor such as a phototransistor or an LDR (cadmium sulphide cell) can tell you both things.

In other words, what do you really want to sense:
a) the switch is closed.
b) the light is on.

ak

________

all i need to know is whether the load is connected to the plug or not.
i think i can use a shunt resistor with differential amplifier.

 

[AnalogKid]

That doesn't get you isolation from the AC line. I vote for the optocoupler. With a low cost generic opto, in its simplest form the interface is 1 resistor and 1 diode. Note that the resistor will dissipate over 2 W. You can decrease that with a capacitor rated for connection to the AC line.

ak