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Low-Cost 50MHz Frequency Meter; Mk.2

This update of our very popular compact 50MHz Frequency Meter now has an internal battery pack or can run from a DC plugpack supply. It also incorporates a 10kHz rounding mode to enable 36MHz R/C transmitters using pulse position modulation (PPM) to be measured with an unambiguous reading.

By John Clarke

At a glance...

  • Compact size (130 x 67 x 44mm)
  • 8-digit reading (LCD)
  • Automatic Hz, kHz or MHz indicator units
  • Prescaler kHz, MHz and GHz indicator units
  • Three resolution modes including 10kHz rounding
  • 0.1Hz resolution up to 150Hz
  • 1Hz resolution up to 16MHz
  • 10Hz resolution above 16MHz
  • Battery or DC plugpack supply

Since many of our readers will not be familiar with the 50MHz Frequency Meter presented in the October 2003 issue, we are presenting the design in full. No doubt kitset suppliers will bring out the updated version of the kit but many readers will want to update a kit they have already built. This is easy to do because there are only a few circuit and hardware changes and the PC board itself is unchanged.

Click for larger image

As far as the circuit is concerned, the major change is in the PIC microcontroller. We have used a PIC16F628A instead of the originally specified PIC16F84P, because we needed a larger memory. Other changes include an LM2940CT-5 low dropout regulator instead of the 78L05, an additional toggle switch on the front panel and the aforementioned internal battery pack. In other respects, the circuit is unchanged.

Frequency meters are used in virtually all areas of electronics and are invaluable for servicing and diagnostics. Among other things, they are ideal for checking the operation of oscillators, counters and signal generators. This unit is auto-ranging and displays the frequency in Hz, kHz or MHz.

This makes it easy to read, as it automatically selects the correct range for any frequency between 0.1Hz and 50MHz and inserts the decimal point in the correct place for each reading.

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