Uwe Zimmermann writes:
>are you really sure about that?
>You have a natural delay in Martin's circuit, since the D output will
>not instantaneously flip back to the high-state once the reset signal
>disappears, but only after 8 external clock signals.
That is what I was thinking, also. The 7493 appears to be
resetting itself properly as I presently have the two Reset inputs
tied to Outputs D and C which means that the counter hits 12 just long
enough for this value to propagate to the logic in the 7493 that
clears the stages. It must be completely clearing everything because
I have the correct frequency at the output and it does not appear to
have any noise problems. I bet that the issues a couple of you raised
might surface if I was running the counter at or near its maximum
rated frequency since any added propagation delays such as the MUX on
one of the two reset lines would tend to make the reset pulse possibly
stay around too long or wait too long to happen. At the 2.4 MHZ
clocking speed, this is probably not going to be a problem.
Thank you for the suggestion of the 74xx157 etc devices.
Now I know what to be looking for.
In case anyone is curious, the device I am building is kind of
an odd thing. It is an audio chopper modulator that will have four
set frequencies of 50, 60, 100 and 120 HZ. When I transcribe old
tapes to CD, I want to be sure the speed is as close to the original
as possible. Most recordings unwittingly have a frequency standard in
the form of either acoustical or electronic mains power hum in the
background. The chopper will provide a reference frequency with which
to beat the background hum. It should make for some weird audio, but
all I am interested in is adjusting the tape speed until the beats
slow down to hopefully nothing. It is sort of an audio strobe disk.
I should know soon if it was worth all the effort or if I used a few
20-year-old chips to make everybody sound like they starred in "Star
Wars." I think ring modulators are what they used to create some of
the special audio effects.
Martin McCormick WB5AGZ Stillwater, OK
OSU Information Technology Division Network Operations Group
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Author: Martin McCormick
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