I actually do have that in place as well, and unfortunately
I couldn't eliminate that transistor.  The original version
of this boost gauge used a DIP switch for dim/bright, and I
coded the park-light signal to that since it was simple.

Here's the real fun part -- my Audi has a lot of other red
LED's (which is what the boost gauge was built to match)
and somehow it detects dark, dims the LED's gradually, and
slowly raises the backlighting on the analog instruments.
Although I could use a separate photocell for this, it would
be really sweet if I could find that signal and use it for
the boost gauge as well.

Cheers,
-Neil.



-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Bob Ammerman
Sent: Friday, June 14, 2002 4:12 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [PIC]: Component reduction...


> Actually, the LED's are on 1/3 of the time, not 1/12.
>
> So far, I've found that muxing (with driver transistors) at
> 20mA is bright enough.  And actually too bright at night.
> In this case, it should be the same, but I thought if it
> got to be a problem, I could always drop to some 10mA LED's
> etc.
>
> Cheers
> -Neil.
>

Neil,

If you really want to get cute you could sample the instrument cluster lamp
voltage (via a voltage divider) with another analog input and use it to
perform duty cycle brightness modulation of your LEDs.

Bob Ammerman
RAm Systems

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