The project was created to turn a multimeter into a sensitive frequency counter with a wide counting range.

An old frequency counter can be upgraded using this project and the range can be extended up to 2.5GHz. A prescaler will be described by this project with very high input sensitivity as it works up to 2.5GHz. The input frequency will be divided with either 1000 or 10.000 by the prescaler. The divider ration is set by a jumper or switch and the divided output signal is 0/5 volt and can be connected as it is to the instrument. 






Most multimeters can measure frequency, but they are not sensitive and the max frequency is not always so high.
The same problem can be found with older frequency counters.

This project will describe a prescaler which will work up to 2.5GHz and with very high input sensitivity.
The prescaler will divide the input frequency with either 1000 or 10.000.

The divided output signal is 0/5 volt and can be connected to your instrument as it is.
The divider ration is set by a jumper (switch).
A PIC 16F84 handle all communication to the prescaler.

Example:
I have a frequency of 100MHz.
I set the divider to 1000.
The output signal from the divider will now be 100e6/1000 = 100.000Hz.
My multimeter show me 100.0kHz 
If I now change the divider to 10.000, the output will be 100e6/10000 = 10.000Hz.
My multimeter show me 10.0kHz 

Shematic



The main part of this project is the PIC16F84 and a prescaler LMX2322.
The input of the LMX2322 is symmetrically at pin 7 and 8.
The input impedance is about 100 ohm and with R7 you form an input impedance of 50 ohm.
Transistor Q1 forms a buffer for the output frequency which is the divided signal.
The output is TTL level and can be directly connected to any instrument.
SW1 is the switch that set the divider ration.

If SW1 = Off the divider ration is 1000.

If SW1 = On the divider ration is 10.000.

Download source file for PIC16F84