-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of David Duffy
Sent: 24 March 2002 22:13
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [EE]: digital volume for tones

> > A quick 'n dirty way of remote controlling volume that I have used
in
> > the past (with great success) is to use an LDR (LDR's for stereo)
with a
> > small 6Volt grain of wheat lamp sandwiched between them and shoved
into
> > some cable insulation and driven direct from an I/O pin
> >
> > The attack /decay times are slow and are well suited for audio and
the
> > signal is also Opto isolated so no problem with earth loops.
> >
> > Because the response time is slow you could PW modulate the lamp at
very
> > slow rate, 10Hz would be your lower limit

Olin asked:
>Is there any reason you didn't use an LED instead of an incandescent?
The
>LED would take less current for the same brightness, is more rugged,
should
>last much longer, and is probably cheaper.

The lamp has a slow response time - the LED hasn't. With the LED, you
would
hear the 10Hz PWM. The incandescent lamp smooths it out nicely ! (LPF)
Regards...

The LDR's response is very slow taking something like 20sec's to go from
say 150 Ohms to 20 Meg so the lamps thermal inertia is really of no
consequence.

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