How to Design Schematic Circuit of Tone Activated Relay

 This circuit can be used to recognize a tone by its frequency. When this tone

is present in a circuithe relay is energized, which could supply power to a

selected appliance.

Wired to the output of a receiver, the circuit can be used as part of a tonemodulated wireless remote control.The receiver can be a common FM radio

or an infrared receiver, depending on the intended application.

The circuit can be used with tones ranging up to 1O0,0OO Hz. The circuit is

tuned by P1.

Inputs of other units can be wired in parallel to get a multi-channel remote

control system. Take care to avoid using harmonic frequencies.

The schematic diagram of the Tone Activated Relay is shown in Figure 1.

The heart of the circuit is the LM567 lC, a National Semiconductor PLL (PhaseLocked Loop) that drives the relay through transistor Q1.

Components placement on a homemade printed-circuit board is shown in

Figure 2. Placement isnot critical, but when operating in frequencies above

50,000 Hz it is important to avoid long connections.

The relay is any type with a 6V coil and current rated for values between 10

and 100 mA.

Position of the polarized components, such as the diode and electrolytic capacitor, should be observed.

To use:

Wire the output of an audio generator or audio oscillator to points X and Y.

The signalshould have amplitude in a range between 100 mV and 1 V peakto-peak for best results. Adjust P1 to trigger the relay. Reduce the signal amplitude and trim P1 for the best performance.

Parts List -Tone-Activated Relay

lC1 - LM567 Integrated Circuit (National)

Q1 - 8C558 general-purpose PNP siticon transistor

D1 - 1N914 general-purpose silicon diode

P1 - 100,000 ohm trimmer potentiometer

K1 - relay - 6V - see text

R1 - 10,000 ohm, 114W,5% resistor

C1, 4 - 0.1 uF ceramic or metal film capacitor

C2 - 0.022 uF ceramic or metal film capacitor

C3 - 0.O47 ceramic or metal film capacitor

C5 - 100 uF,12WVDC electrolytic capacitor