Digital scale - frequency meter. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Digital scale - frequency meter. Encyclopedia of radio electronics and electrical engineering

Free technical library

Encyclopedia of radio electronics and electrical engineering / Digital technology

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The idea of developing a digital scale came to me a long time ago, but I decided to implement it only after my friend made a frequency meter by Peter Halicky (Peter Halicky OM3CPH).

At first glance at the OM3CPH circuit, it can be seen that it can be greatly simplified by replacing the switch and transistor switches with a single 555ID7 microcircuit. It was the first urge to own development.

Later, when studying the OM3CPH program, an incorrectness in the program was discovered, which led to a periodic measurement error. In total, in the range of 0-35 MHz, there are 52 sections in which the frequency meter is wrong. This is easy to detect if you measure the GSS frequency, for example, and smoothly tune it up by a few megahertz. It will be seen that the frequency meter smoothly increases the readings to a certain frequency, then sharply decreases, and after a while returns to the correct values. Those who wish can explain the essence of this error, but that's not the point. The discovery of this trouble was the second urge to develop the program too.

So this frequency meter was born - a digital scale.

Its capabilities:

Measures frequency up to 25 MHz (did not try further);
In the digital scale mode, adds the measured values to a constant when applying a log. "0" to output J3;
In the same mode, it subtracts modulo a constant from the measured value when applying a log. "0" to output J4;
If you submit a log. "0" simultaneously to the outputs J3 and J4, then after 1 sec. the scale will switch to the constant recording mode, display the letter "F" and the measured frequency on the indicator.

Resubmission of the log. "0" on J3 and J4 will write the measured value to the non-volatile memory of the processor and return to the measurement mode. After that, the new constant will be used as the value of the intermediate frequency. This mode is made so that users can set the IF value on their own scale without reprogramming the PIC processor.

1. Schematic diagram

2. Printed circuit board (click to enlarge)

Digital scale - frequency meter

You can take the program for self-programming of the frequency counter processor here.

When developing the circuit and software, data from the design of Peter Halicky OM3CPH were used.

Publication: N. Bolshakov, rf.atnn.ru

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