This little circuit will enable a remote controlled switching of an appliance situated in the next room using the concept of power line communication, which involves the use of home mains wire for transferring data in the form of high frequency pulses through the mains wire, superimposed over the existing mains frequency.
Power Line Communication Concept
The idea was published in the datasheet of the IC LM567 as one of the application circuits, among the many other outstanding ones.
The IC LM 567 is actually a specialized tone decoder using PLL technology which enables the device to detect and respond only to a specific frequency as determined by an external RC network values, and reject all other irrelevant frequency in the spectrum.
The proposed remote control circuit using power line communication may be witnessed in the above diagram, the circuit functioning details may be learned from the following points:
How the Circuit Works
R1, and C1 are the external RC components which decide the sensing frequency of the device, and pin#3 becomes the sensing pinout of the IC.
Meaning, pin#3 will detect and acknowledge only that particular frequency which is set using the R1/C1 network. For example if the R1, C1 values are selected to assign a 100kHz frequency, pin#3 will pick only this frequency to activate its output and ignore all that may be different to this range.
The above feature enables the IC to single out the specific frequency from the superimposed AC 50 or 60 Hz frequency and trigger the output only in response to this predetermined set frequency.
In the figure we can see a small isolation transformer which is included in order to isolate the electronic circuit from the lethal mains current.
The mains low AC frequency acts like the carrier frequency, over which the triggering high frequency rides to reach the intended destination across the transmission line.
In the above receiver design, the IC is assigned to respond to a 100kHz frequency which is supposed to be injected into the mains line from a nearby location which could be an adjacent room or premise.
The 100kHz frequency could be injected through any oscillator circuit such as a IC 555, or IC 4047 circuit or another IC LM567 circuit installed as the transmitter unit.
In an event when a signal is injected into the mains from a relevant location, the receiver circuit shown above detects the specific frequency in the attached mains power line, and responds to it by producing a low logic across its pin#8.
The pin#8 being connected with the a 4017 flip flop circuit toggles the output relay and the load ON or OFF depending upon the previous situation of the relay.
The Transmitter Stage
The transmitter which is supposed to inject the 100kHz or the desired triggering frequency into the power line can be ideally built using a half bridge driver oscillator circuit as shown below:
The 12V input to the circuit must be switched through a push button arrangement so that the circuit is triggered only when required in order to switch on the intended appliance through the power line.
The RC component at pin2/3 of the IC are not calculated for generating 100kHz, The following formula can be used for determining the right oscillator frequency:
f = 1/1.453× Rt x Ct
Ct is in Farads, Rt is in Ohms. and f in Hz
Alternatively the same can be evaluated using a frequency meter and with some experimentation.
Warning: The circuits presented above involve mains voltages which can be lethal, therefore extreme care and precaution is advised during the procedures.
This is an untested circuit designed as per the suggestions presented in the datasheet of the IC LM567