Interpretation of a NE567 proximity wireless detector circuit

　　NE567 Audio Decoder/PLLIC

　　NE567 is a built-in PLL circuit with an AM lock detection and output drive circuit. The main function of NE567 is to drive the load (usually LED) when the frequency in its detection band is at the input of the IC. The center frequency, input band, output delay, etc. can be programmed using external components. The functions of NE567 IC include 0.01Hz to 500kHz frequency range, highly stable center frequency, programmable bandwidth, high noise suppression, output absorption of 100mA, external adjustable VCO frequency, etc. NE567 , common applications are highly immune to false triggering, dual audio decoding, remote control, ultrasonic control, monitoring frequency, 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 of the IC (pin3) is in the detection band. Resistor R7 and capacitor C4 set the oscillation frequency. These oscillations are picked up at pin 5 and it is coupled to the terminal of the assembly using capacitor C3. Terminal B picks up the base oscillations of transistor Q1, and couples through capacitor C1. Q1 and Q2 form a two stage collector base biased 2 stage amplifier. R1 and R4 are base bias resistors, Q1 and Q2 collector. C2 couples the output of the first stage to the second stage. The signal is picked up, thereby amplified and applied to the input pin (pin3) of the IC through capacitor C7. 5233 forms the output filter capacitor and capacitor C5 determines the bandwidth of the received signal. C9 is a bypass capacitor from the power supply. C2 and R2 provide a phase shift to the VCO signal and this phase shifted signal from the IC is detected by the IC. When some object is picked up near the assembly, the capacitor between its terminals changes. This capacitance changes with the frequency change, the IC detects this change and displays the indication. Resistor R8 limits the output LED current.