Being the sole electronics engineer within my family and close circle of friends, I find myself unable to decline requests for assistance at times. Recently, I received a request from a friendly elderly lady residing in a retirement home. In her room, the light switch near the door and the pull cord above the bed control the ceiling light fixture located in the middle of the room.
However, she wishes to have these switches operate her standing lamp instead since there isn’t a ceiling light fixture in her room. This standing lamp is equipped with an on/off switch on its power cord and is plugged into an electrical outlet. Unfortunately, the lamp is positioned quite far from her bed, making it challenging for her to navigate in the dark. Although using a wireless remote-controlled power outlet is an option, it’s not ideal due to the risk of misplacing the remote. Or is it? Let me introduce a viable circuit solution.
Setting Up the Wireless Control System
To begin, acquire a wireless power point and a suitable enclosure that accommodates both the remote control and a small prototyping board. Construct the circuit on the prototyping board following the provided schematic. Carefully open the remote control and solder wires to the ‘on’ and ‘off’ push buttons. Verify their polarity; if polarized, connect them to the 4N25 optocouplers as illustrated in the schematic, ensuring pin 5 has a higher voltage than pin 4.
Operational Process of the System
Here’s how the system operates: the user activates the pull cord or light switch, initiating the flow of mains voltage to the transformer. Consequently, the relay engages, charging capacitor C1. During this charging process, a minor current passes through optocoupler 1.
As a result, the ‘on’ button on the remote control is essentially pressed. The remote control triggers the corresponding power point, to which the standing lamp is connected, turning it on. Simultaneously, capacitor C2 starts charging. If the user pulls the cord again or operates the switch near the door, the relay disengages, causing C2 to discharge through optocoupler #2. This action operates the ‘off’ contact of the remote control, extinguishing the light. The remote control continues to function using its standard battery, and the white enclosure replaces the light fitting on the ceiling.
Ensuring Controlled Discharge and Operational Integrity
For safety and proper functionality, diode D1 ensures the discharge of C1 when the relay disengages. Additionally, D2 ensures that C2 discharges solely across optocoupler 2, preventing any unwanted discharge across the relay.