Frequency change produced in Colpitts oscillator by metal object near tank coil is indicated by 565 PLL connected asfrequency meter. Oscillator frequency increases when search coil is brought near nonferrous metal object. Oscillator frequency decreases, as indicated by lower meter reading, when coil is brought nearferrous object. Signetics Analo

g Data Manual, ``Signetios, Sunnyvale, CA, 1977, p 856 858. (View) This stabilized voltage-to-frequency converter features 1 Hz-1. 25 MHz operation, 0. 05% linearity, and a temperature coefficient of typically 20 ppm/ °C. This circuit runs from a single 5-V supply. The converter uses a charge feedback scheme to allow the LTC1052 to close a loop around the entire circuit, instead of simply controlling the offset. This approach enhances linearity and stability, but introduces the loop`s settling time into the overall voltage-to-frequency step-response characteristic. (View) This receiver is built around a PC1373 IR remote-control preamplifier, a sensitive 30-to-40 kHz tuned detector, an autoniatic gain control, a peak detector, and an output waveshaping buffer. The demod-ulated signal from the preamp stage is sent to IC4A, a 74C14 Schmitt trigger. The squared-up 1 500-Hz signal is then sent to the clock input of IC5A, half of a 4013 dual D flip-flop. That 750-Hz signal is clipped to approximately 0. 7-V p-p by diodes D3 and D4. The clipped signal is then fed to IC6, a 567 tone decoder. The output of that IC goes low whenever the frequency of the signal fed to it is within the lock range of its internal VC0. When IC6 detects a signal of the proper frequency, pin 8 goes low. The output signal is fed through another Schmitt trigger (IC4B), which drives another D flip-flop, IC5B. Schmitt trigger IC4B also drives IC4C, which in...

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