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dsehrawat • Dec 1, 2015

Circuit to remotely control an electric switch


I have been trying to design an electric/electronic circuit to allow remote controlling of an electrical device (say, a bulb) in addition to its existing switch (electrical switch). A couple of issues:
1) I am finding it really difficult to synchronize between a) digital control (via a relay) and b) physical switch control.
2) I am using ACS 712 current sensor to detect if physical switch is switch on or off; so that MCU can take appropriate action (such as, if required, override physical switch on logic and turn the switch off). It's quite sensitive to change in temperature (if circuit left switched on for some time) and that results in a lot of noise in the output reading of ACS 712.

Attaching a snapshot of my circuit.


Any ideas to resolve this issue...or suggestion of a better circuit?
Harshad Italiya
Harshad Italiya • Dec 6, 2015
@dsehrawat :
From the detail what I understand is you are facing issues in sensing the physical switch as you are using current sensor in it. And the detail that you shared which says even temperature changes are making the noise and switch can malfunction so same thing can happen when you are turning Relay ON and OFF because of EMC/EMI you might get interference and that is giving you false signal.
How if you use sense the mechanical switch by any other way? Like using Opto coupler to MCU?

lal • Dec 7, 2015
It looks to me that circuit breaker will trip the very instant H-switch is switched On or Relay-2 is powered from the wiring diagram. I see a direct short between Phase and Neutral there.

I was thinking, what if the voltage between H-switch terminals be monitored instead of current. Voltage is measured with high impedance devices which would cause negligible current flow and hence much less EMI.

Potential difference across the switch will be zero when the switch or Relay 2 is ON. And it will be equal to supply voltage when both are off.

The logic would then be,
If Out2 = 0 and voltage between H-switch != 0
Then H-switch is ON.

Position of H-switch doesn't matter if Relay-2 is activated.
dsehrawat • Dec 7, 2015
Thank you Guys...Appreciate that...I thought of using Voltage sensor at the very inception; but because of one basic flaw it was causing me issues; Positive voltage should be on the other side (away from bulb) of H-switch.
Also, it was my bad...The bulb should be in series with this circuit (rather than in parallel).

Thanks a ton for all the are doing a gr8 job in handling this website venture.

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