DIY Frequency Counter And Crystal Testing Kit

DIY Frequency Counter And Crystal Testing Kit
(1 Hz to 50 Mhz)

 

Last month I had ordered a frequency counter and crystal testing kit from Alixpress for $2.57. In the kit you will get the main pcb, 7 element display, PIC16F628 , 3 transistors , resistors, capacitors ,small trimmer, 20Mhz crystal, a push button switch . It was designed by DL4YHF but now it is sold by chinese sellers on Ebay and Alixpress .

Lets Start Soldering It

Prepare your soldering station and let the iron properly  heated up. First start soldering resistors and other small   components. And then solder the big components like 7 segment display and the PIC 16f628 IC etc. After completing the soldering, check for any un-soldered point and clean the flux out of the pcb . 

 

Testing

Power it via the port or directly by 5v to 9v dc .The regulator 7550 will regulate the voltage and will provide 5v to the whole circuit. When the circuit will get power all the 7 segement display will glow and then the second last display will display a 0. I have some crystals of 10mhz , 12mhz , 8mhz and some of 3.57mhz and 4.494mhz . Plug in the crystal in the crystal input. 8 Mhz was showing 8.0001 and  it was preety accurate , 12mhz was 12.002 . When I Plugin 3.57 Mhz and a 4,494 Mhz it was showing some different readings 😞(read further to know how to fix that ). For testing the frequency counter I gave signal from my Taurus 20m Receiver and the the counter gave me a perfect reading about the frequency I was listening to. It can measure the frequency upto 50mhz.

Troubleshooting The Problem Of  Reading Low Frequency Crystals

For solving the problem of reading Xtals below 4 or 6 Mhz crystals , I added a 47pf or 22pf disc capacitor parallel to C3 near the transistor 2SC9018 . After doing this modification to the circuit , the xtal tester was giving the accurate reading of 4.494 Mhz xtal and 3.57 Mhz xtal . But the reading of xtals like 8mhz ,12 mhz ,21 mhz was different . Main problem is caused by the oscillator circuit ( we need to change the design or I can add a switch to activate the capacitor parallel to C3 ).

Conclusion 

It needs some modifications and changes in the oscillation circuit for testing the crystal frequency but if you want to use it as a frequency counter then it is a good option .

Thanks for reading the blog .
Regards
VU2COR 
Satnam Singh