[Diy_efi] WB 36 LED Display dimmer

[Daniel R. Nicoson]

Bruce,

Thanks for the reply.  I may dig into this over the next few weeks.  I'll
post if I accomplish anything.

Take care,

Dan Nicoson

-----Original Message-----
From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org]On
Behalf Of bcroe at juno.com
Sent: Thursday, April 01, 2004 7:56 PM
To: diy_efi at diy-efi.org
Subject: [Diy_efi] WB 36 LED Display dimmer


1 Apr 2004  "Daniel R. Nicoson" <A6intruder at adelphia.net> writes:

> Is there a simple modification that would allow me to add a dimmer
> to the LED's?  That display is great but sometimes could use a
> dimmer.  I haven't had a chance to pull the data sheets on the chips
> involved.

> Dan Nicoson

I KNEW someone would ask that, sooner or later.  The brightness
is controlled by resistors R2, R4, R5, and R8.  Note 2 & 4 are 3/4s
the value of 5 & 8, due to different voltage across them.  Say,
doubling values would half their current, which would also half
all LED currents.  I would try 1st putting in values like 8 times
these and see if thats the right dimming.  Once adjusted,
connect  a resistor like the original to pin 6-7 of each LM3914.
Tie the other end of each resistor to the anode of a 1N4004.  Tie
the 4 '004 cathodes together.  When the 4 cathodes are grounded
by a switch, the second resistors will increase the brightness.

You could also get a linear control using a 4 output current
generator, or a pulse width modulated LED supply.  A lot more
complicated.

Bruce Roe
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