[Elecraft] ATTN LED low level activity

[Don Wilhelm]

Ron,

That has to be a K1 that you are dealing with, although you did not 
state it.
When BAT is selected, the MCU samples the voltage produced by the R6 and 
R7 voltage divider.  When ATTN is to be indicated, the MCU pulls pin 3 
to a low state which turns on the LED.
I suspect you are seeing the result of brief negative going pulses 
between intervals when the voltage is sampled at the MCU pin 3.
I do not see any evidence of that behavior with a 13.8 volt power 
source, but I suspect it may become evident with a low supply voltage.
As you indicate, it should not be a big deal, but is only "interesting 
behavior".

73,
Don W3FPR

On 9/29/2015 11:20 PM, ron hansen wrote:
> Just finished receiver portion of build on unit ser no 3388. Everything
> working so far but I discovered a strange condition with the ATTN LED.
> Whenever the display is set for BAT voltage the ATTN LED very dimly flashes
> at about 10 times per second. The flashing is sort of random and only
> happens when BAT is selected. Seems like this control is coming from the
> PIC, there is no other input to the LM358...
> Not a big deal, otherwise the ATTN LED works fine..
> Ron
>
>