The LM567 is a practical single audio decoded integrated circuit. The integrated circuit is low, less peripheral components, only 2 resistors and 3 capacitors in typical applications. The main function of the IC is to determine the frequency of the external signal. The comparison result is made into voltage output by phase comparison with the frequency of the internal circuit oscillator through the frequency of the input signal. With this feature, the frequency gauge generator shown in Figure 1 is designed. Figure 2 is a block diagram of the internal circuitry of the LM 567, and the models of the LM567 are completely converted to NE567, SE567, and HA567.
Since the LM 567 has the characteristics of high input sensitivity (20-200mV) and input impedance high (20kΩ), a less component can be configured to form a pocket frequency meter. The working principle is: The detected frequency signal is detected from the LM5673 feet, and a plurality of signals are sent as input signals. LMM5675, 6 foot external RC (W + R2 and C4 ~ C6 in Figure 1) and the internal oscillator signal also feed into the detector and the signal frequency and phase of the delivery, compared the signal within the bandwidth range, by it After the internal zoom is enlarged, it outputs a low level by its 8 foot. If there is no signal input, the 8 foot is high (same VCC). The drive current of its output signal is 100 mA. In FIG. 1, when the frequency timing is measured, the signal needle (self-made) is given from the CK, and W (the capacity of K1 conversion C is required if necessary) causes the oscillation frequency F0 generated by the LM567 internal oscillator to track the external input frequency FIN. When FIN = F0, the LM5678 foot output is turned low by a high level, and the LED is lit. The frequency value indicated by the multi-ring potentiometer with a pointer is the measured frequency FIN. The role of D1, D2 is to limit the amplitude of the FIN. Protect the security of the LM567.
When the circuit is used as a signal generator, the plug is unplugged, and the left end of C1 is grounded by the socket CK. LM5673 foot pair AC short circuit (prevent external interference), at which time the circuit is a signal generator. The signal of the signal generator is output by the VT emitter. Due to the simple circuit, the printed circuit board can be designed according to the selected shell. The C1 in Figure 1 preferably uses a hazardous capacitance. If there is no or the size is too large. Two 100μF / 6.3V electrolytic capacitors can be connected to the two-positive and two negative electrodes.
This signal generator is ready. The focus is to adjust the calibration, that is, the calibration of the multi-circular potentiometer pointer. The scale can be performed with a standard signal generator or a digital frequency meter. If the K1 transforms the three-speed frequency, when the scale cannot be overwritten, it can increase or decrease the C5 and the C6 value is achieved.
This instrument can also simultaneously perform a signal generator at the same time as measurement frequencies. Do not affect each other. According to the illustrated parameters, the sensitivity is 200mV, the conversion switch K1 can make the frequency in 100 Hz-500 kHz, and the relative error is in 1% to 5%. The frequency timing error is less than 10%, the error is large in the low frequency, and the high frequency segment is small, which is a shortcoming of this frequency. .
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