RE: LED lighting

["Dave McLaughlin" <dave@xxxxxxx>]

Hi David,

Yeh, I am building a small board just now to test the PWM out to see if it
will work with the devices I plan to use. I'll let you know how it goes.

The Mega128 is the next device I plan to get cracking with. Have a small
PCB
design already in place, just need to send it away some time soon.

I was thinking about putting CAN bus on it because I could use the
MCP25050/5 from Microchip which is a standalone CAN IO device with 2 PWM
outputs.

The battery power idea could be a great solution for LED lighting fitted in
addition to normal mains units. With a simple setup designed for the mains
and a low cost UPS, you could have lighting for quite a reasonable time in
the event of a power failure.

Regards
Dave...
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-----Original Message-----
From: David Yeend [mailto:david.yeend@xxxxxxx]
Sent: 31 October 2003 12:42
To: ukha_d@xxxxxxx
Subject: RE: [ukha_d] LED lighting


Dave,

I have been thinking about this as well but along the lines of the
functionality of the iCove tubes previously discussed on here.

I was thinking of running 3 PWMs, each one connected to a different
colour, to create a mix of RGB with perhaps a 4th PWM to vary the overall
duty cycle and provide the brightness control - I have not tested yet but
that was the theory.

One thing I have had problems with in the past is the response time of
LEDs. I found that an LED with slow response would not allow dimming
without
noticable flicker. Hit the LED with too fast a signal and it simply
illuminated a an uncontrollable dim level.

I know that with PWM we are not talking about altering the drive current
but I have seen white and blue LEDs generate different coulors under low
drive current conditions. I was wondering if trying to drive an LED with
too
fast a signal may also cause similar results?

I know you use Atmel parts - the Mega128 has 6ch PWM so it could be
possible.

The Qprox idea is a nice touch, would you also implelemt 485/232/CAN or
something for remote control and status feedback etc?

You could also consider the same controller as being able to offer a
battery powered emergency / power cut lighting facility - embed a few LEDs
in the ceilings and turn them on when to power dies?

I wish I had the time.......

Regards,

David

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