[Elecraft] K2 voltage sense

Mon Aug 18 14:08:00 2003

Hello Ed

>My K2 displays 0.3 volts lower than the voltage I measure on the =
cathode
>side of D10.  (This is after the diode drop of 0.2V)  I verified the =
voltage
>divider R9/R10 had the proper voltage.  Also pin 7 of U3 and pin 5 of =
the
>MCU U6 show the expected voltage.  Pin 1 of U6 reads 5.13V on the DVM.

> Is this within the expected error for the A to D conversion on the MCU =
U6?

This is not an error in U6.  U6 is using 5.13V as the callibration =
reference.
In other words, it has been told that 5.13V is 5 volts.  So, this will =
throw
everything off by a little bit.  In particular, 13.4 volts becomes =
pretty
close to 13.1 volts.

I guess you could go through a pile of 78M05 regulators to find one that =
puts out
exactly 5.00 Volts.  Mine works the same way though.  I figure that =
everything
is within design specifications.  The 78M05 is spec'd to put out 5V give =
or
take 200 mV.  So nothing is "wrong".  It might be nice to have a tighter =
reading
on the battery voltage, but I figure I'll just remember the difference.  =
It
matters a bit more for the watt meter.  The SWR meters on the antenna =
tuners
have pots to calibrate them, so it is OK.

73, Michael, AB9GV
K2 #3430.

Thanks,

Ed KG4ARN  #3212

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