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3.5GHZ Frequency Counter


Frequency counter is a very important test instrument for Radio Amateurs, especially those who wish to develop or test circuits. There are lots of frequency counters in the market but building one was never so easy & exciting with Microprocessors doing lots of work for us.

This Frequency counter Project is based on PIC16F84A Microprocessor chip manufactured by Microchip and software provided by amateurs to help understand PIC programming.

I made this project on a single PCB for the reasons that my idea of a counter was to make it a portable and independent of bench supply. (Because I already have a bench frequency counter) In this counter, we have possibility to supply external 12V or have a 9V internal battery.

Two RF inputs are available, switched by a push switch to select "Direct" or "Pre-Scale" Which gives you selection of either Low VHF (to 35MHZ) or VHF/UHF measurement ranges.

Counter software is auto-ranging and drives a 16×1/2 LCD. Counter is designed on a 6 × 19cm PTH Double Sided PCB. I could make this board much smaller but I preferred this size, keeping in mind first time kit builders.

This documents provides schematics & completed pictures of the Frequency Counter.

Picture of the Completed Frequency Counter Top Side View:

Lower right section is pre-scale area comprising 4 ICs, one pre-scale chip & few components. These parts will be available later as an up-grade option.

Counter Input Section View: 

Note: upper section is 3.5GHZ pre-scale circuit and bottom section is low frequency input circuit components.

Frequency counter Top View with LCD module removed:

Two main chips of counter circuit, PIC16F84A & 74HC132 are fitted on the other side of the board. H1 header is visible below LCD header, which is used to select two types of HEX files.

Picture of Frequency Counter - Back Side, where PIC16F84A is installed:

In above picture, PIC16F84A and Pre-scale IC, which is a SMT device, are not fitted.

Four holes on the right hand side, below red push button switch are for 9V battery holder, when internal supply is used.

Schematic of the 35MHZ PIC 16F84A LCD Frequency Counter:

Click to enlarge

Schematic of 3.5GHZ Pre Scale Section Up-Grade:

Click to enlarge

Some Design Notes:

  • Frequency counter is designed on a single PCB of size 6cm × 19cm Double Sided PTH.
  • If you do not like low frequency input circuit but want a TTL level input, you may place a jumper between J3 and C15, and do not install all the components of 50MHZ input amplifier.

Picture of Personalize message at start-up:


Programming Hex 16F84A

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