WB-LED display

[Mark S. Riley]

I was starting to look at it when your message came in. Yes, I did reverse
R3 and R14 along with pins 3 and 12 on the LM2902. Also had the 2 leads from
the rich side and lean side LM3914 to pins 5 and 10 on the LM2902. All
backwards and it still worked not bad. Well, I straightened it all out. What
I did was not reference the right pins from underneath the perf board. Got
almost all of them backwards. Changed them to correctly match the wiring
diagram but I still had the J3 and J4 backwards. Seemed like the steps were
right but now the display was backwards. Switched the J3 and J4 wires so
that now they were connected to the correct pins on the LM2902, J3-pin 3 and
J4- pin 12. Now the rich side steps correctly, 1.75 volt  is about 12 or 13
from center. But, now from 2.47 volt up, the entire lean side is lit
continously unless the voltage drops down to or below 2.47 volt. Then the
rich side looks normal but as soon as the voltage goes up to 2.48 or more it
lights all 20 lean led's. Have I blown the LM2902? Or what else do you
think?  I'm going to get it right yet. Thanks for the suggestions. Mark

Oh, and by the way, I got the red and green backwards. red to rich and green
to lean. I don't know how I was looking at it, in a mirror I guess.
----- Original Message -----
From: <bcroe at juno.com>
To: <diy_efi at diy-efi.org>
Sent: Monday, October 01, 2001 5:03 PM
Subject: Re: WB-LED display


> It sounds like you're pretty close.  No LEDs at 2.5v.
>
> 2.75 Vout is 17.93 A/F.  That should just about turn
> on 8 lean LEDs.
>
> You should get 20 LEDs on the rich side for Stoich
> minus 1.129 V, or 1.371V.  1.75 Vout is 11.2:1 A/F,
> which is about 13 rich LEDs.
>
> Sounds like the gain is too high on the rich side and
> too low on the lean side.  If you switched R3 and R14,
> it would do that.  Check that you have S + 2.5V, or about
> 5V on pins 6 & 7 of U2 and U10.  You might set it up
> on the bench and feed in fixed votages to double
> check everything; hard to do when everything is
> bouncing around.
>
> What color LEDs did you use?  Anything will work, but
> I prefer red for lean and green for rich.
>
> Bruce Roe


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