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Date: Wed, 02 May 2001 12:11:21 -0700
From: Wayne Burdick <n6kr at elecraft.com>
Subject: Re: [Elecraft] K1 Backlighting

Hi Andy,

>   First, it looks like signal "6A" (MCLR + control strobe?) decides whether
> to enable LEDs in general (parm is stored in U3). Is this correct? Sorry
> guys, but a lot of these devices weren't around when I learned digital in
> 1970!

The 6A line is on all the time. LEDs are enabled or disabled internally
in firmware, then controlled by the indvidual lines shown in the front
panel schematic. Unfortunately there are no spare control lines
available; the reason the schematic is a bit confusing is because some
microcontroller pins are used as both inputs and outputs depending on
whether they're turning something on/off or reading an ADC input.

The best way to control a separate back-light LED is to put a miniature
slide or toggle switch on the left side of the K1. This switch can
supply 12V to the backlight directly.

Note: If you do mount a switch on the left side, mount it forward of the
front panel 2-D fasteners. Otherwise it may interfere with the
soon-to-be-announced KBT1 internal battery option, in case you want to
install it, too.

73,
Wayne
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