Small-sized frequency meter - digital scale on the microcontroller, up to 200 MHz with LCD display

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Small-sized frequency counter-digital scale on the microcontroller, up to 200 MHz with LCD display. Encyclopedia of radio electronics and electrical engineering

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Rice. 1. Diagram of the device (click to enlarge)

Small-sized frequency meter - digital scale on the microcontroller, up to 200 MHz with LCD display

The frequency meter has small dimensions of 65x35x20 mm and fits easily in the palm of your hand. Despite this, it operates in a wide frequency range from 0 to 200 MHz, and can also be used as a digital receiver scale.

Main technical parameters:

measurement time - 1/2 s
measuring ranges:
- from input 1 - 1...200 MHz (±1 kHz) or 1...30 MHz (±100 Hz)
- from input 2 - 1...4 MHz (±10 Hz)
- from input 3 - 0...1 MHz (±2 Hz)
Uin min - 50 mV
Uin max - 5 V
Upit - 7...15 V
Ipotr - 40 mA (Upit = 9 V)

In digital scale mode, the device works with receivers having IF: 455 kHz, 465 kHz, 500 kHz, 10695 kHz, 10700 kHz, 21000 kHz, 24000 kHz. You can select +IF or -IF. Individual firmware for any other inverter is possible. The basis of the device is a programmable microcontroller AT90S1200-12SI from ATMEL. The controller controls the LCD display HT-1611 and, depending on the installed jumpers, works as a frequency meter or a digital scale. To power the microcircuits, a voltage regulator 78L05 is used, which determines the lower limit of the supply voltage not lower than 7V.

If it is necessary to reduce the lower limit of the supply voltage down to 5V, the 78L05 regulator should be replaced with the LM2931Z5. To work from input 1 at frequencies up to 200 MHz, a high-frequency divider LB3500 from SANYO is used, due to which the sensitivity in the range of 1 ... 200 MHz is not worse than 50 mV. When operating at low frequencies (input 3) 0...1 MHz, the internal comparator of the microcontroller is used, which ensures high sensitivity and reduces the dimensions of the board. All parts of the device fit on a 65x35 mm board. The microcontroller is installed from the side of the printed tracks. The LCD display is soldered into the board from the side of the parts. At the same time, the height of the device together with the indicator does not exceed 20 mm.

Description of operating modes:

To work with "In1" jumper Pr1 is installed.
To work with "In2" jumper Pr2 is installed.
To select the measurement range, contact pads (KP) 1 and 2 are used, which are shorted to ground or left free:
1...200 MHz - KP1 and KP2 are free;
1...30 MHz - KP1 is closed, KP2 is free;
1...4 MHz - KP1 is free, KP2 is closed;
0...1 MHz - KP1 and KP2 are closed.
To select the inverter when operating in the digital scale mode, KP 3,4,5,6 are used, which are shorted to ground or left free:
+ FC - KP3 is free;
-FC - KP3 is closed;
0 kHz - KP4 is free, KP5 is free, KP6 is free;
10700 kHz - KP4 is closed, KP5 is free KP6 is free;
455 kHz - KP4 is free, KP5 is closed, KP6 is free;
465 kHz - KP4 is free, KP5 is free, KP6 is closed;
500 kHz - KP4 is closed, KP5 is closed, KP6 is free;
10695 kHz - KP4 is closed, KP5 is free, KP6 is closed;
21000 kHz - KP4 is free, KP5 is closed, KP6 is closed;
24000 kHz - KP4 is closed, KP5 is closed, KP6 is closed.

Author: Igor Maksimov, maksi@metax.kharkiv.com; Publication: cxem.net

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