[sdiy] LEDs and noise

Neil Johnson neil.johnson71 at gmail.com
Fri May 8 17:34:13 CEST 2015


Tim Ressel wrote:
> In my experience, for example designing the Livewire Chaos Computer, you need to go from a positive rail to ground, use a separate 'dirty' ground just for the display stuff, and make sure you have enough local capacitance to handle the glitch current.

In the world of professional audio mixing desks, which have rather
large numbers of switched LEDs, the general solution is a string of
LEDs between the rails, fed by a constant current source (transistor,
three resistors), and with transistors or switches across the LEDs to
short them out when you want them off.  This eliminates current being
dumped into ground, and eliminates switching transients which even
with a local capacitor to help localise the current surge you still
end up switching a current around a loop with a sharp rise and fall,
which will generate a magnetic pulse that will couple into other
circuits.

Neil



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