NE567 tone decoder / PLL IC.
NE567 is a tone decoder IC from Philips.
The IC has a built in PLL circuit with AM lock detection and an output
driver circuit. The main function of NE567 is to drive a load (usually
LED) when a frequency with in its detection band is available at the
IC’s input. Center frequency of the input frequency band, output delay
etc can be programmed using external components. The features of NE567
IC includes 0.01Hz to 500KHz frequency range, highly stable centre
frequency, programmable bandwidth, high noise rejection, can sink 100mA
at the output, highly immune to false triggering, externally adjustable
VCO frequency etc. The common applications of NE567 are touch tone
decoding, remote controls, ultrasonic controls, frequency monitoring
etc.
NE567 proximity detector circuit.
A simple proximity detector circuit using NE567 is shown here. Pin 8 is
the output terminal of the internal output driver circuit inside the IC.
This pin goes low when the input frequency to the IC (at pin3) is with
in the detection band. Resistor R7 and capacitor C4 sets the frequency
of oscillations. These oscillations are available at pin 5 and it is
coupled to the terminal A of the pick up assembly using capacitor C3.
Terminal B picks up the oscillations and couples it to the base of the
transistor Q1 through capacitor C1. Q1 and Q2 forms a two stage
collector to base biased 2 stage amplifier. R1 and R4 are the collector
to base biasing resistors for Q1 and Q2. C2 couples the output of first
stage to the second stage. The picked up signal is thus amplified and
applied to the input pin (pin3) of the IC through capacitor C7. C6 forms
the output filter capacitor and capacitor C5 determines the band width
of the receiving signal. C9 is a power supply by pass capacitor. C2 and
R2 provides a phase shift to the VCO signal from the IC and this phase
shifted signal is detected by the IC. When some object comes near the
pick up assembly, the capacitance between its terminals change. This
change in capacitance changes the frequency ,IC detects this change and
shows the indication. Resistor R8 limits the output LED current.
Notes.
- Use 9V DC for powering the circuit.
- If you are using an AC adapter, then it must be well regulated and free from noise.
- The pick up assembly can be made using two metal strips.
- POT R6 can be used for adjusting the sensitivity.
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