logarithmic F to V, tuning ref

gstopp at fibermux.com gstopp at fibermux.com
Mon Jan 6 23:44:58 CET 1997

     I've built a crystal-based A-440 reference that runs off of a single 
     +5 volt supply. It consists of an oscillator module with a frequency 
     of 10.1376 MHz, followed by a divide-by-10 counter, followed by a 
     divide-by-9 counter, followed by a divide-by-256 counter. The first 
     two dividers are formed out of 74HCT191 counters using the carry-out 
     to preload-in modulus trick, with the carry pulse clocking the next 
     counter. The last counter is made from a 74HCT393.
     The final 440 Hz square wave is passed through a pair of 100K/0.01uF 
     passive low-pass sections, followed by an op-amp buffer (1/2 of an 
     LM358), followed by a 0.15uF/47K high-pass section to center the 
     waveform around zero volts. The output is a line-level waveform that 
     is nearly sinusoidal.
     - Gene
     gstopp at fibermux.com

______________________________ Reply Separator _________________________________
Subject: logarithmic F to V, tuning ref 
Author:  klund at MIT.EDU at ccrelayout
Date:    1/4/97 8:02 PM

Also, I've been thinking about how to build a stable tuning reference. 
I'd like to come up with a box that just produces a 440 hertz tone.  The 
only way that I've thought of for real stability is to use a crystal and 
count it down.  Searching through the Digikey catalog, I was only able 
to find one crystal that was an integer multiple of 440, 11 MHz.  That 
still requires a 25,000 division, which will need a 15 bit counter. 
That's not too complicated, but does anyone have another idea?

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