Difference between revisions of "Frequency Counter"

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** [https://owenduffy.net/blog/?p=11386 DL4YHF 50MHz counter on a Chinese TB-244746 PCB]
 
** [https://owenduffy.net/blog/?p=11386 DL4YHF 50MHz counter on a Chinese TB-244746 PCB]
 
* Frequency range: 1 Hz-50 MHz
 
* Frequency range: 1 Hz-50 MHz
* Crystal Test Range: 4 MHz-48 MHz - Replaced with pre-amp circuit
+
* Crystal Test Range: 4 MHz-48 MHz
 +
** Mods to replace crystal checker with sensitive pre-amp
 
* PCB size:8*5.3cm
 
* PCB size:8*5.3cm
 
** Fits in 100 x 60 x 25 mm enclosure
 
** Fits in 100 x 60 x 25 mm enclosure
 
* Source - [https://www.aliexpress.com/item/4001262793719.html?spm=a2g0o.productlist.0.0.a6a57b558PTLGq&algo_pvid=77bddd5c-6ae2-4082-8837-73945f792fae&algo_expid=77bddd5c-6ae2-4082-8837-73945f792fae-0&btsid=0bb0622f16000865130548256e846c&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_ AliExpress Frequency Counter] - Very inexpensive
 
* Source - [https://www.aliexpress.com/item/4001262793719.html?spm=a2g0o.productlist.0.0.a6a57b558PTLGq&algo_pvid=77bddd5c-6ae2-4082-8837-73945f792fae&algo_expid=77bddd5c-6ae2-4082-8837-73945f792fae-0&btsid=0bb0622f16000865130548256e846c&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_ AliExpress Frequency Counter] - Very inexpensive
 
* [https://github.com/TheHWcave/PIC-freq.counter-modification/ PIC-freq.counter-modification]
 
* [https://github.com/TheHWcave/PIC-freq.counter-modification/ PIC-freq.counter-modification]
* Mods to replace crystal checker with sensitive pre-amp
+
*
  
 
== Built into case ==
 
== Built into case ==

Revision as of 14:06, 1 November 2020

FreqXounter-Kit-Assembled-02.PNG

Features

Built into case

  • P-Touch white on black labels

FreqCounter-P181-720px.jpg

Plastic 100x60x25mm-720px.jpg

Power 5-1mm.PNG

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

FreqCounter-Case-11-720px.jpg

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

FreqCounter PreAmp Schematic.PNG

When building kit, do not install

FreqCounter DoNotInstallParts.PNG

Cuts/Jumpers

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

FreqCounter Rework PCB Front.PNG

  • Green = Back side cuts

FreqCounter Rework PCB Back.png

  • Short etch on one cut

FreqCounter Rework-Cuts-Back.PNG

  • Details of preamp input pin

FreqCounter Rework-06.PNG

  • With parts

FreqCounter-P177-720px.jpg

  • Wire on back

FreqCounter Rework Wires Back.PNG

Testing

FreqCounter InCase.jpg

  • 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

Fixing the frequency error

  • Replaced 22 pF cap with 2 series 33 pF caps
    • Far right near variable cap

FreqCounter-P177-720px.jpg

  • Added 22 pF to back of board
    • Upper mid right

FreqCounter-P180-720px.jpg

  • Why was this an error?
    • Perhaps the variable cap is too small for proper loading of the crystal
    • Could possible parallel a 10 pF cap with the variable cap?

Firmware Mods

Reviews / Builds