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Driving chastotomera- digital scale on the PIC-16F842

See also:

Specifications:

Maximum measuring frequency. .................. 50 MHz
The maximum resolution of the measured frequency ... 10 Hz,
Input Sensitivity .............................. .250 mV
Supply voltage ………………………………. 8 ... 12,
Current consumption ....................................... .. 35 mA,

Schematic diagram of frequency - digital scale is shown in Figure 1. It consists of:

  • input signal generator provided on the transistor VT1. The signal measured by the frequency supplied to J5 input is limited, amplified and fed to the processor PIC input for measurement;
  • CPU U1, performing the measurement, calculation, conversion, control of dynamic display and dynamic polling of the input signals. Conclusions J3 and J4 are used to select a digital scale. Processor clock frequency is determined by a crystal Y1 and may vary within a small range capacitors C3 and C4.
  • U2 LED indicator to display the frequency.
  • U3 chip - position decoder digit displayed.
  • Integral regulator U4 the supply voltage. Supply voltage frequency value 8..12 volts is supplied to the terminals J1 (+) and J2 (-)

Functions are implemented as follows:

  • When you deactivate the J3 and J4 operates as a frequency (measurement mode);
  • When a log. "0" at output J3 adds the measured values ​​with pre-stored in nonvolatile memory constant (digital scale);
  • When a log. "0" on the output J4 subtracts modulo this constant from the measured value (digital scale);
  • When a log. "0" on both J3 and J4 conclusions 1 sec. scale constant enters the recording mode, the display will show the letter "F" and the measured frequency.
  • Resubmission of the log. "0" on the J3 and J4 will lead to the recording of the measured values ​​in non-volatile memory of the processor and return to the measurement mode. Thereafter, a new constant is used as the value of the intermediate frequency.
  • This mode is made in order to allow users to set their own drive value in their scale without reprogramming PIC processor. By default, the text of the program is recorded equal to the value of 5.5 MHz IF.

Approx. a logical "0" corresponds to the potential of 0 volts ( "earth").

The structure is made on a one-sided PCB dimensions 57 x 67 mm. Design the printed circuit board shown in Figure 2, however, the ultimate simplicity of the design makes it easy to repeat it even maketnitse.

Properly assembled frequency - digital scale with a properly programmed PIC processor requires almost no configuration. The minimum setting is applied to the input frequency of the reference frequency and the tuning capacitor C3 to display correctly on the display. This may require an adjustment capacitor C4.

Driving chastotomera- digital scale on the PIC-16F842

Printed circuit board

PCB frequency.

Publication date 22.03.2003gg.