[sdiy] Cheap frequency counter for oscillator calibration

[Harry Bissell]

I don't think a frequency counter is the way to go. they are too slow if they are accurate enough.

I use a good guitar tuner to set the frequency of an external sine wave oscillator, then use
lissajous patterns on an oscilloscope to beat the unknown VCO against that reference. Its easiest if the VCO
has sine or triangle outputs, but possible with a ramp. Square waves are nearly useless for this tuning.

You can easily discern about a 4:1 ratio in each direction, if you set the fixed oscillator midrange you can
get an eight octave range.

Its much easier to tweak trimpots until the pattern stops rotating, and your ear can tell you if you are
in the right octave range...

Strobe tuners are another option.

I made myself a precision 1V/step calibration box so I can change input voltages easily and be sure
they are repeatable. this makes the job a lot easier

my vote: frequenct counter is useless...

H^) harry

----- Original Message -----
From: Karl Ekdahl <elektrodwarf at yahoo.se>
To: synth-diy at dropmix.xs4all.nl
Sent: Thu, 22 Apr 2010 08:57:44 -0400 (EDT)
Subject: [sdiy] Cheap frequency counter for oscillator calibration

Hi list

I'm looking to buy a cheap ($50-$200) frequency counter mainly to be used for calibrating the span and base tuning of analog oscillators - any suggestions? Is there a better way of doing this then just measuring the frequency?

Thanks

Karl


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-- 
Harry Bissell & Nora Abdullah 4eva