AC frequeny

Archiver

Hi,

I am trying to measure, if it's possible, 3 different frequency's at
about 9 VAC. I am trying to measure 9KHZ, 11KHZ and 14KHZ. Is it
possible to do this with a BS2 and if so, where can I find
information about it?

Thanks,

Chris

Archiver

In a message dated 5/31/2003 6:28:08 AM Pacific Daylight Time,
CHRIS@R... writes:

> Hi,
>
> I am trying to measure, if it's possible, 3 different frequency's at
> about 9 VAC. I am trying to measure 9KHZ, 11KHZ and 14KHZ. Is it
> possible to do this with a BS2 and if so, where can I find
> information about it?
>
> Thanks,
>
> Chris

It can be done with a stamp. Also, how much accuracy do you need.

There may be many ways to do this, the approach I would take is as follows
(assuming the AC signal is very clean .....very few noise spikes)

1) Use a half wave rectifier on your AC signal, and set up an op amp voltage
comparitor with hyterisis that will trigger at about 1 or 2 volts. Use an
"open collector"type to you can tie the output to +5 volts via a resistor
(4.7k).

Or if you don't want to use the 1/2 wave recitfier, use and opto-isolator and
feed the AC intor the "diode side/" Connect a resistor to +5 volts on the
collector of the "transitor" side.
Then use the op amp comparitor on the collector of the opto isolator
transistor.

This will convert your AC into a TTL compatible square wave.

2) Using the stamp, there is a pulse in command that will measure the input
pulse period (high period or low period) with 10uS resolution.

3) can set up a loop that will sense a logic 0 from the converted sine wave,
once the low is detected, then jump to a sub that will measure the high time
of the pulse. This is assuming the AC signal is always there, because there is
a "timeout" the stamp will do while waiting for the pulse, if the pulse does
not come within a certain period of time, it will return 0.

RESOLUTION....14khz has a period of 71 uS, but the stamp can only return a
value of 7 (7 X10uS)....so you will lose some resolution.

An alternative command you can use with the stamp is COUNT, it will count
pulses on an input pin for a period you define...

Once you know the period of the pulses, or the number of pulses in a period,
of course you can get the frequency.....

Hope this gets you started.

Ken


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