Chip frequency meter. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Measuring technology
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Digital integrated circuits can also be used to design a frequency meter, in which the upper limit of reading can reach several megahertz. The figure shows a diagram of a frequency meter using a single vibrator in an integrated design. It has four measurement subranges: 10...100, 100...1000 Hz, 1...10, 10...100 kHz. If the radio amateur has a switch for a larger number of positions, then the number of sub-ranges can be increased by selecting the necessary capacitors and resistors accordingly.
(click to enlarge)
The duration of the pulse generated by the device depends on the capacitors C2 - C5 and resistors R3 - R6. The voltage from the output of the microcircuit (pin 6), proportional to the frequency of the input signal, through the diode VD5 charges the capacitor C1. The voltage on this capacitor is indicated by the PA1 measuring device, and its scale is graduated in units of frequency.
The frequency meter is adjusted in the following order. Switch SA1 put in the position of measuring the minimum frequency subrange (this corresponds to a larger value of the capacitor section SA1.1). Apply a signal with a frequency of 100 Hz to the input from the exemplary generator by adjusting the tuning resistor R3, set the arrow of the indicator RA1 to the last division of the scale. Sequentially transfer the switch to the following positions and, each time increasing the frequency by 10 times, adjust the maximum deviation of the indicator needle with the appropriate tuning resistor.
Resistors and capacitors of any type can be used in the design of the device. As an indicator head, a device of a magnetoelectric system with a total deflection current of 500 μA should be used. You can also use a less sensitive measuring head, for example, with a total deviation current of 1 mA, but in this case the reading becomes somewhat more complicated, and in the device it is necessary to increase the capacitance of the capacitor C1 to 25 μF, and reduce the resistance of the resistor R2 to 3,9 kOhm.
In the design of the device, the recommended microcircuit can be replaced with the domestic K155AG1, and KD521A can be used as diodes. When a signal is applied in TTL levels, diodes VD1 -VD4 can be excluded.
Author: G.Kuzev
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