Frequency meter. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Measuring technology

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The parameters of the proposed frequency meter are given in table. one.

This frequency meter, in my opinion, has a number of advantages compared to the previous ones:

- modern cheap and easily accessible element base;
- maximum measured frequency - 200 MHz;
- combination of a frequency meter and a digital scale in one device;
- the possibility of increasing the maximum measured frequency up to 1,2 GHz with a slight modification of the input part of the device;
- the possibility of switching during operation up to 4 FC.

Frequency measurement is carried out in the classical way: counting the number of pulses for a fixed
time interval.

The schematic diagram is shown in Fig.1.

The input signal through the capacitor C4 is fed to the base of the transistor VT1, which amplifies the input signal to the level necessary for the normal operation of the DD2 chip. The DD2 193IEZ chip is a high-frequency frequency divider, the division factor of which is 10. Due to the fact that in the K1816BE31 microcontroller used, the maximum frequency of the counting input T1 is f = Fkv / 24, where Fkv is the frequency of the quartz used, and in the frequency meter Fkv = 8,8672 MHz, the signal from the high-frequency divider is fed to an additional frequency divider, which is a decimal counter DD3. The frequency measurement process begins with zeroing the divider DD3, the reset signal of which comes from pin 12 of the microcontroller DD4. The permission signal for the passage of the measured signal to the decimal divider comes from pin 13 DD4 through the inverter DD1.1 to pin 12 DD1.3.

At the end of a fixed measurement time interval, a high level appears at pin 13 DD4, which, through the inverter DD1.1, prohibits the passage of the measured signal to the divider DD3, and the process of converting the accumulated time pulses into frequency begins, as well as preparing data for display.

(click to enlarge)

This device has the ability to work in both high-frequency and low-frequency ranges. When working in the low-frequency range, switch S1 must be set to the upper position and the signal should be applied to input 2 (pin 9) of the frequency meter board. To measure the frequency from 1 Hz to 20 MHz, it is necessary to use the shaper proposed in [1].

The program of the microcontroller is in the ROM DD8, the DD5 chip is used to multiplex the addresses of the microcontroller. ROM firmware for operation of the device as a frequency meter is given in Table 2.

To obtain the maximum efficiency of using the microcontroller, the device uses dynamic indication.

When using this device as a digital scale, it is necessary to apply a high level to pin 22 DD8 using switch S2.3. The choice of the IF value is made by connecting the pins 10,11 of the DD4 chip to the ground. Input 3 (pin 5) of the frequency meter board is designed to turn on the selected intermediate frequency (for example, when switching from reception to transmission). While the device is operating in the digital scale mode, the low-order digits of the indicator show hundreds of hertz. The operation of the device in the digital scale mode corresponds to a different ROM firmware.

Printed circuit board (pic.2, pic.3, pic.4) is made of double-sided fiberglass with dimensions of 100x130 mm. The indicator is mounted directly on the printed circuit board with two clamps from a conventional mounting wire. A socket is provided for installing the DD8 chip. When wiring the board, it was necessary to place the transistor VT1 as close as possible to DD2. Around VT1 and DD2, as much foil as possible is left on both sides in order to shield high-frequency circuits. In the design, IV-1 is used as an indicator HL18 as the most popular in amateur radio designs. If it is necessary to miniaturize the design, the indicator IV-18 can be replaced by IV-21, which has much smaller overall dimensions. In this case, it is necessary to reduce the heating voltage and the negative voltage at the cathode according to the passport data. It is desirable to use the DD1 chip in the 1533 series as a higher frequency one.

To power the frequency meter, you can use the power supply, described in detail in [2]. It is only necessary to increase the voltage from -20 V to -30 V and the filament voltage - up to 4,8 V when using the IV-18 indicator. In the indicated power supply circuit, it is desirable to replace the KD503 diode with a KS133 zener diode, which eliminates false illumination of the indicator segments.

Adjustment of the frequency meter should begin with a check for an open circuit of all, without exception, the connecting conductors of the printed circuit board, then check for the absence of a short circuit of the connecting conductors adjacent to the printed circuit board. Immediately after energizing the frequency meter, check the current consumption by voltage +5 V. It should not exceed 250 mA. Then measure the voltage at the VT1 collector, it should be within 2,0 V ... 3,0 V. The specified voltage is set by selecting the resistor R3. With error-free installation,

serviceable parts and the absence of errors in the program, the final adjustment of the device consists in accurately setting the frequencies of the master oscillator of the microcontroller using capacitor C7 in accordance with the readings of the exemplary frequency meter.

Thanks to the software-controlled measurement process, it is possible to use non-decimal high-frequency dividers by slightly changing the microcontroller program. The author tested microcircuits 193PP1 (division ratio - 704), 193IE6 (division ratio - 256) in this device. Tests have shown that the maximum frequency of the measured signal reaches 1 GHz. The 193PTs1 microcircuit turned out to be the most preferable, because. it has an input amplifier. The K181BE51 microcontroller can be replaced with K1816BE31, K1830BE31, K1830BE51 or their foreign analogues - 8031, 80S31. In the absence of a 193IEZ chip, you can replace it with a K500IE137 chip, turning it on according to a typical circuit.

Literature

1. Biryukov S. Digital frequency counter//Radio. - 1981.-№10.-C.44.
2. Khlyupin N. Digital frequency meter // Radio amateur. - 1994. - No. 11.
3. Stashin V.V. Design of digital devices. - 1990.

Author: A. Gritsyuk, Makeevka; Publication: N. Bolshakov, rf.atnn.ru

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