[sdiy] Signal indicator board...

[Czech Martin]

What about using an analog meter together with a simple log
circuit? Some hold feature could be added (peak detector)
in order to capture short overload. Would look good on an analog synth.
Depends on what you want to do. Digital recording has no headroom
above 0 dB, so an overload lamp with memory is needed.

Switching LED chains means 10mA pulses or so.
This could introduce some clicking noise into sensitive
circuits via capacitive or galvanic coupling,
perhaps, if the layout is very bad even via magnetic
coupling.


m.c.

-----Original Message-----
From: Grant Richter [mailto:grichter at asapnet.net]
Sent: Freitag, 2. Mai 2003 19:20
To: Tim Ressel; Synth-Diy
Subject: Re: [sdiy] Signal indicator board...


This may interest you...

All the VCAs in the Wiard modules use an LM339 quad comparator chip to form
a 4 section VU meter. Like an LM3916, but with only 4 sections. An LM339 can
be found as cheap as $0.29 each (quant. 200) whereas an LM3916 runs around
$2.00.

Use a resistor divider like this:

+15V 5.1K 6.8K 2.2K 680 330 Gnd

This gives you (roughly) reference voltage levels of 10V, 3.3V, 1V and 0.33V
which correspond (again very roughly) to levels of +20, +10, 0 and -10 dBv.

Ideally, this should be a bi-polar circuit with an absolute value circuit in
front of it. So you indicate both positive and negative waveform peaks. If
you make the simplifying assumption that audio waveforms are ALWAYS centered
around 0 volts, you can ignore the negative peaks, and eliminate the 2
additional op-amps needed for the absolute value circuit.

The 10 volt level corresponds to 20 volts peak to peak and is a clipping
warning. LED colors I used are Green, Green, Amber, Red for -10, 0, +10 and
+20.

Tie the 4 negative comparator inputs together and to a 100K to ground, use
as an input (high impedance). Run the reference levels to the positive
comparator inputs. Connect the LEDs with current limiting resistors between
+15 and the comparator open collector outputs. 10 resistors, 4 LEDs, 1 chip.


> From: Tim Ressel <madhun2001 at yahoo.com>
> Date: Fri, 2 May 2003 09:00:53 -0700 (PDT)
> To: Synth-Diy <synth-diy at dropmix.xs4all.nl>
> Subject: [sdiy] Signal indicator board...
> 
> Yo,
> 
> I've been thinking (dangerous, I know) and I think
> what the world needs is a little board that takes in a
> signal and has two LEDs to show signal present and
> overload. This makes a handy visual indicator as well
> as a swell panel filler. Real simple circuit, possibly
> surface mount to keep sizes small. It could be
> single-supply to keep wiring down.
> 
> So like, what do ya think??
> 
> --Tim
> 
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