This frequency counter uses your existing digital multimeter as the display unit that is why it can be constructed at very low cost.
Due to the high impedance of most DMMs, a frequency to voltage converter can be easily connected to it without matching problems.
The converter shown in the diagram has a frequency range of 10 Hz up to 1 kHz (position A) and 1 kHz up to 100 kHz (position B). The sensitivity at
low frequencies 10 Hz up to 1 kHz is around 35 mVpp and increases to 350 mVpp at a frequency of 100 kHz.
- First, temporarily connect the junction of R6/R7 to pin 12 of flip-flop FF2 instead of pin 13.
- Measure the voltage at C6 (the meter must be in 20V range).Switch S1 to position A and adjust P1 to read a voltage (at your meter) of 2.93V.
- Finally, reconnect the junction of R6/R7 to pin 13 of FF2.
- Then, switch the meter to 2V range and adjust P2 to give a voltage of 1.875V.
The DVM you are going to use must be connected to the plus and minus terminals of the converter's output.
The conversion in A range is 1 kHz= 1V and in B range is 100 kHz= 1V.
External Wiring Layout
Electronic Circuits volume 1.0 - Circuit Nr. 71
The complete data of the electronic circuit described above can be found in the following book and is available from Amazon.com.
Click on the image to view the book.