This streamlined configuration creates a remote-controlled switch that receives its control signal through the mains voltage. The switch is activated using the ‘mains remote transmitter,’ detailed in another section of this publication. To connect this transmitter, a switch needs to be placed between pins 1 and 2 of K1, which can be either a press contact or a make contact depending on the specific application.
The concept behind the ‘mains remote switch’ involves energizing a relay to establish a connection between the mains voltage at K1 and K2. The ‘receiver,’ a term somewhat overstated for this straightforward design, consists of Tr1 and the tuned circuit L1/C4. The C1/Tr1/C2 network forms a coupled circuit tuned to the transmitter’s frequency of 143 kHz. The selectivity is determined by L1/C4, primarily influenced by the standard suppression coil L1. T1 provides the gain necessary to operate the relay. The amplified signal, smoothed by C6, supplies the voltage required to drive T2 into conduction, activating the relay.
Enhancing Receiver Sensitivity with Voltage Biasing
To amplify the receiver’s sensitivity, a bias voltage for T1 is established through the voltage divider configuration formed by P1, R1, and R2. This setup enables the relay to be energized even without an incoming signal. The prevention of excessive conduction is ensured by D1, which stops C5 from charging further and restricts T1’s conductive state. The circuit relies on the incoming signal’s strength overcoming the relay’s hysteresis for proper operation. Upon the signal’s absence, the relay naturally returns to its de-energized state.
Addressing Sensitivity Challenges
It is important to acknowledge that this circuit’s simplicity comes with a drawback: its sensitivity might be lacking depending on specific household conditions. One potential remedy is adjusting the transmitter frequency to fall between 95 and 125 kHz. Correspondingly, modifications in the values of C1, C2, and C4 are necessary, making it an endeavor suitable for readers keen on experimentation. Remember, once activated, the entire circuit is connected to the mains potential, mirroring the transmitter’s setup.
Mains-Powered Transistor Stage and Relay Control
Power for both the transistor stage and the relay is derived directly from the mains voltage using a capacitive voltage divider. R5 acts as a current limiter for diodes D4-D7 during the initial power-on phase. The diodes provide rectification, and C7 filters the output. C8’s low impedance ensures ample current flow. The no-load voltage is capped by zener diode D3 when T2 isn’t conducting, preventing excessive voltage. R6 and R7 serve to discharge C8 promptly after disconnection, averting any residual dangerous voltage. Test points A and B facilitate testing and allow alternative components to be energized (bearing in mind the circuit’s connection to the mains network). The relay’s pinout follows standard conventions, enabling the use of alternative relay types with a 24 V operating voltage and an operating current not exceeding 28 mA, as long as these specifications are met.