[NA-User] Paddle Port Problems

David A. Pruett k8cc at comcast.net
Sat May 1 23:34:09 EDT 2004


Measure the voltage on high end of the pullup resistors.  Generally this is 
connected to pin 14.  It should be pretty close to +5 VDC, say a minimum of 
4.5V.  Then check the voltage on the dot and dash inputs (with no paddle 
action).  These should be close to the pullup voltage value.

The problem is that pin 14 is not really designed to source much 
current.  If the dot and dash inputs cannot be pulled up (through the 10K 
resistors) then NA reads the inputs as low and makes the keyer go 
da-dit-dah-dit-dah etc.

I have seen LPT ports where the pullups are not necessary, but these tended 
to be on older computers with LPT cards having discrete parts.  Laptops 
seem to be the worst, since everything is designed to minimize power 

How to fix it?  The guaranteed way is to remove the pullups from LPT pin 14 
and use a good +5V supply for the pullups.  This is what the SO2R boxes do, 
but in that case it's a no-brainer because there's usually a +12V power 
supply to run the switching relays so it's a simple matter to add a zener 
or three-terminal regulator to make +5V.  It's a lot more inconvenient 
adding this to a standalone keying interface, particularly if it's built 
into a D-shell.

You can try changing the value of the pullup resistor.  If the pin 14 
voltage is OK, but the dot and dash voltages are low, try reducing the 
value of the resistors.  If everything is too low, and about the same, try 
increasing the resistor values.

As a last resort, try changing the LPT port.

I have ten logging computers at K8CC, plus an old Dell laptop I use for 
trips, and these all have correct paddle operation from pin 14.  Newer 
stuff seems to be more troublesome (I hope we're not encountering a trend :-().


At 07:18 PM 5/1/04 -0500, Robert Pack (NX5M) wrote:
>This is happening on both 10.58 as well as 10.59.
>New computer has been added to the station.  Setting up for WPX CW I have 
>discovered that when the paddle port is enabled (LPT1) all I can get is a 
>continuous dit-dah-dit-dah.  All else works just fine.
>Nothing worked at first until I made changes in the bios.
>I have used 3 different interface cables (known to be working) and even 
>one that does not have the paddle port input added to it with the same 
>Paddle port enabled......it is stuck in dit-dah.  Paddle port 
>disabled......all is well.
>What the heck am I missing?
>Note:  I have also noticed the same thing on one of the old 120 machines.
>NA-User mailing list
>NA-User at contesting.com
>NA on the web:  http://www.datomonline.com/

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