Enhanced TCA440 detector

Posted on Feb 5, 2014

This circuit may look simple, but that`s because I made considerable effort to simplify the circuit. It requires only a small amount of components and it has low current consumption (15 mA). From the left to the right, this circuit consists of a tranducer, a simple transistor pre-amp, a TCA440 IC that contains an oscillator and mixer, a second-ord

Enhanced TCA440 detector
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er low-pass filter and a audio-amp consisting of a LM386 IC. The transducer that is used is a piezo-electric transducer, which is quite sensitive but unfortunately has a relatively limited frequency range. By connecting a coil parallel to the transducer, the response can be broadened somewhat, at the expense of decreasing overall sensitivity. The signal from the transducer is first amplified by a simple transistor stage, consisting of a single BC550C transistor. It is biased for a current of approximately 0. 7 mA. The capacitor from the emitter to ground causes a +6 dB/oct gain slope for frequencies higher than 16 kHz. After this it enters the TCA440 at pin 1. In the TCA440 this signal is multiplied with the signal of a built-in tuneable oscillator. The oscillator can be tuned with the use of the potmeter connected to pin 6, from about 18 kHz to 100 kHz. The potmeter must be connected such that it has the lowest resistance when the wiper is turned counterclockwise. This gives a reasonable linear relation between wiper position and tuning frequency, but means that CCW is highest frequency and CW is lowest. The oscillation frequency is determined by the product of the capacitor between pins 5 and 6 and the resistor going from pin 6 to the positive supply connection. The highest frequency is therefore set by the 1n8 capacitor and the 2k resistor, while the lowest oscillator frequency occurs when the circuit sees a 2k+10k=12k...

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