[sdiy] frequency counter

[Elliot Williams]

On Fri, 23 Oct 2009 21:39:08 -0700
"David G. Dixon" <dixon at interchange.ubc.ca> wrote:

> Hey Team!
> 
> Has anyone here ever built an audio range frequency counter?  I'd like to
> build a reasonably accurate frequency counter module for my synth to use for
> VCO tuning.  Any info would be much appreciated.

Here's three solutions.

For a stand-alone module, the Maxim ICM7224/5 chip.  http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1359.  It is a counter with LED-digit drivers built in.  Hook up a 1 sec input pulse to the counting pulse and you're measuring DC to 20kHz with 1Hz resolution.  

If you can program micros, I'd just use a PIC/AVR.  Running an AVR on a crystal will get you fantastic accuracy.  The big advantages here are that you don't have to implement a 1 sec pulse circuit, you can do long-run moving averages and/or implement a variable timebase, and you can use basically anything as your output/display. 

Finally, there's a family of clever circuits that read out on regular LEDs in binary that are based around two counters: one used as a timebase/latch and the other doing the actual counting.  See http://www.hanssummers.com/radio/sfreq/index.htm and related links.  For our low-frequency work, you'll want to drive it with a watch crystal and/or use a second 4060/4040 dividing down the timebase.  

The downside of these circuits is that you have a strange binary readout.  The upside is that you can get all the parts from your bin + a clock from the dollar store, and you get to improve your binary.

(I'm gonna make an AVR one right now just for fun.  Thanks for the inspiration.)

         Elliot.