[Elecraft] Check Your Buttons [switch current is _not_ too low]

[Wayne Burdick]

David G3UNA, wrote:
> A quick look at the circuit diagram shows that buttons are taken  
> from a
> potential divider to CD74HC4051M inputs.  These switches (unless I've
> misread the diagram) will therefore take the input current of the
> multiplexer which is typically <1uA.  I don't know the spec for the  
> Elecraft
> switch but a similar one requires a minimum current of 10uA.  This  
> should be
> checked more rigorously, but it might indicate a potential problem.
David,

The K3's front panel switches do not have a minimum required current.  
I just verified this again with the manufacturer. They have gold- 
plated contacts on the PC board and should be extremely reliable.

Regarding the switch test function in the menu: A small amount of  
digit flicker is perfectly normal. The A to D converter has an  
ambiguity of +/- one count, and the firmware algorithm reading the  
switch has no hysteresis, therefore +/- count of flicker is also to be  
expected.

In firmware, we read the switch voltage several times, average them,  
and look for the proper switch code based on "bins" that have a large  
amount of excess margin. So the operator should not be concerned in  
the least about a deviation of even several counts in their own switch  
read voltages.

If you're experiencing any type of switch-read error that isn't a hard  
failure, it is probably something that I can improve in firmware. I'll  
be happy to work with you on this -- please give me a detailed example.

73,
Wayne
N6KR