Circuit Wiring

The series that we will make this is a special electronic circuit can be used to detect the presence or absence of signal AF / RF. The circuit is very neat and simple to make. Costs it takes quite cheap. If you are already assembling this circuit, then with easy reader determine whether there is AF or RF signal at a particular section of a circuit.

Basic circuit uses an audio amplifier and a loudspeaker with switch input for AF and RF signals. The whole device can be made small as possible so it can be included in a container to maintain security. Audio amplifier section in this series created by IC TDA 2822M, with low stereo power amplifier in 8-pin mini-DIP. IC is used as a bridge cofiguration to shrink to 250 mW output power, loudspeaker handle 4 ohm, 500mW. The current required is less than 10mA with voltage of 3V battery.

When the selector switch in the AF position, working on the input audio signal AF amplifier input (pin 7 of IC 1) through a capacitor C2 and potentiometer VR1. Capacitors C2 always hold input amplifier of the DC voltage and make it happen in the audio signal frequency. Input Signal IC 1 can be arranged with the help of potentiometers VR1.

When the selector switch in position RF and demodulator detector circuit formed by capacitor C1, diode D1, and resistors R1 and R2 are connected to the input The set. When the audio signal is detected then it will actually go kerangkaian to be strengthened. Signal detection is done by plugging probe (probe) on the legs of the existing components.

This circuit is used to convert a mono audio signal into a stereo signal that can be panned between the left and right channel by a 0-10V control signal, it is intended for analog synthesizer systems.

The essence of the circuit is for the input of tone and signal to provide an activation for the relay switch.

• Relay – an electrically operated switch where the current flowing through the coil of the relay is creating a magnetic field which attracts a lever and changes the switch contacts, thereby making its state open or close
• BC214 – a complementary silicon planar epitaxial transistor used in AF small signal drivers and amplifiers as well as for low noise preamplifier applications due to its feature of good linearity of DC current gain
• LM741 – a general purpose single operational amplifier with features such as offset null, compensated internal frequency, voltage range with high input, good stability of temperature, and protected from short circuit

The use of relay will allow the circuit to switch from one condition to another. It can also be referred to as a form of an electrical amplifier since it is able to control an output circuit of higher power than the input circuit. There are many types of relays being used in many electronic and electrical circuits, which include solid-state relay, Buchholz relay, overload protection relay, latching relay, forced-guided contacts relay, mercury-wetted relay, contactor relay, machine tool relay, reed relay, polarized relay, and solid state contactor relay.

Circuit Diagram


The circuit created is sensitive enough to the AC signals in the input stage, where the signals are ranging above 5 mV. It will also be sensitive to react with the human voice signals having a range of frequency from 50 Hz up to 3 KHz. The human voice is a part of the human sound produced primarily by the vocal cords or vocal folds which in turn produces a voice frequency that is used for the transmission of speech.

During the absence of an input signal, the state of the 12 V relay RL1 is at OFF condition as regulated by the 10K Ohms trimmer RV1. The circuit can be made to react with its sensitivity in points A, B, & C, where a negative feedback can be placed due to the addition of band pass filter. The filter will operate only in the 1 KHz range and the circuit will only correspond at this frequency.

Parts List :



The signal and tone activated relay switch were used in a wide range of fields which includes measuring instruments, audio systems, communications equipment, and factory-automation equipment. They can also be found on telephone subscriber circuits for the polarity reversing switch, testing, and ringing functions.