::Tone Decoder Using LM567::

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Tone tone decoder or a decoder is a circuit that serves to detect the presence of a signal with a certain tone. If the signal is the same tone with the tone of a series of internal oscillator the output of the circuit will be active. One of the tone decoder integrated circuit is LM 567.

The LM567 and LM567C are general purpose tone decoders designed to provide a saturated transistor switch to ground when an input signal is present within the pass band. The circuit consists of an I and Q detector driven by a voltage controlled oscillator which determines the center frequency of the decoder. External components are used to independently set center frequency, bandwidth and output delay.

Features

20 to 1 frequency range with an external resistor
Logic compatible output with 100 mA current sinking capability\
Bandwidth adjustable from 0 to 14%
High rejection of out of band signals and noise
Immunity to false signals
Highly stable center frequency
Center frequency adjustable from 0.01 Hz to 500 kHz

Applications

Touch tone decoding
Precision oscillator
Frequency monitoring and control
Wide band FSK demodulation
Ultrasonic controls
Carrier current remote controls
Communications paging decoders

Tone Decoder LM 567

The tone decoder circuit has a main component IC LM 567, as shown in Figure 1 below.

Figure1. Tone decoder circuit.

Oscillator internal frequency of the circuit is:

f = 1/(1,1xR₁xC₁)

If the input signal has a minimum voltage of about 25 mV and the frequency around the frequency of internal oscillator, the output will be low level logic.

Tone decoder circuit can be implemented as a remote control (remote control) circuit, with the following block diagram.

Figure 2. Examples of tone decoder circuit applications as remote control.

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