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
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