"Dave" wrote in message
news:bBBwj.58078$C61.44082@edtnps89...

wrote in message
...
I would like to build an analog volume meter (moving needle type)
using moving needle gauges like this
http://en.wikipedia.org/wiki/Image:VU_Meter.jpg
scavenged from a dead mixer's VU meter.

It would plug into the headphone jack on a set of computer speakers
and monitor the right/left sound volumes independently.

Can anyone point me to a good website or book with schematics or plans
on building this?


PS I would also be interested in building a frequency meter (also
would be plugged into computer speakers and display the pitch/
frequency of a pure sin wave coming from the computer's sound card). I
got several replies but they were pretty technical and I have not
found any complete plans for such a device. If any can suggest a good
web site or book that would be great. Thanks


BobG:
That's a tachometer. A lo pass filter, a comparator, a oneshot, a
capacitor, and a meter on a trimpot. Every zero crossing, the
comparator fires the oneshot, the cap integrates the pulses, and the
meter shows the freq. Cal it with sine waves.... no harmonics.

linnix:
Or a $2 micro averaging the DCT, FFT or XYZ (forgot the name of that
spectral analyser).

whit3rd:
Phase-lock loops like 74HC4046 can lock onto an audio
frequency, and the follower in it has an output voltage
proportional to frequency. That's about $0.60 from your budget;
a good analog moving-needle meter will suck up the rest of it.


test


A crystal controlled monostable multivibrator driving an analog meter. that
is more like 10 bucks without the meter. It can be calibrated without an
input signal. or by inputting a signal beyond its range.


Bob

Bob