Frequency Counter

Features

• Original Design by DL4YHF
  • DL4YHF 50MHz counter on a Chinese TB-244746 PCB
• Frequency range: 1 Hz-50 MHz
• Crystal Test Range: 4 MHz-48 MHz - Replaced with pre-amp circuit
• PCB size：8*5.3cm
  • Fits in 100 x 60 x 25 mm enclosure
• Source - AliExpress Frequency Counter - Very inexpensive
• PIC-freq.counter-modification
• Mods to replace crystal checker with sensitive pre-amp

Built into case

• P-Touch white on black labels

• 100x60x25mm Black Plastic Electronic Project Box Enclosure Instrument Case - Inexpensive plastic case
  • Plastic Waterproof Cover Electronic Project Instrument Enclosure DIY Box Case Junction Box Housing 100 x 60 x 25 mm Black

• BNC connector - female chassis mount
• 5.1mm Chassis mount power connector

• 7-9V in
• Right angle header pins pointing to inside of card
• 4-40 x 3/16” Machine Screws
• 4-40 Standoffs

Rework - Add Pre-Amp

• Re-uses extra HF transistor that would have been used by crystal tester oscillator
• AC coupled input
• Based on

Pre-Amp schematic

When building kit, do not install

Cuts/Jumpers

• Four cuts
  • Blue = 1 front side cut
  • Green = 3 back side cuts
• Jumpers Red

• Green = Back side cuts

• Short etch on one cut

• Details of preamp input pin

• With parts

• Wire on back

Testing

• 4.9152 MHz crystal oscillator
  • Scope frequency counter shows 4.19520 MHz
  • Freq Counter displays 4.9747 MHz
  • Difference = 500 Hz or 0.1% accuracy
• Can only adjust the variable capacitor in narrow range
• Freq = 25,000 MHz - measured = 24.997 MHz
  • Error = 3 KHz / 25,000 KHz = 0.012%
• Freq = 10.000 Hz - measured = 9.999 Hz = .01% error

Firmware Mods

• HiRes_Freq_RPM1234_Event_counter
  • HACKING A CHEAP EBAY FREQUENCY COUNTER