[Elecraft] [K3] K3 driving KK1L band decoder

[Ethan Miller K8GU]

As Joe suggested, I lowered the 3.3k resistors and now it works great.

Thanks for all the input!

73,

--Ethan, K8GU/3.

On Thu, Sep 6, 2012 at 4:07 PM, Joe Subich, W4TV <lists at subich.com> wrote:
>
>> Due to the different impedences between the two it did not work
>> (driving one by itself was fine...but not both). I had to add a
>> buffer circuit between the ACCY output and the band decoder input.
>
> The Quadra has 1K series resistors and its inputs are clamped with
> diodes to +5V/Ground driving a CMOS buffer/line driver configured
> as a switch (input 1/input 2) .  The KK1L decoder has 3.3K series
> resistors to the opto.
>
> In all probability the Quadra is "hogging" the available current
> from the band data outputs and the PS2501 optos are not getting
> enough drive.  Replacing the 3K3 Ohm with 1K Ohm input resistors
> would probably have been preferable.  Even without any loading by
> the Quadra, with the K3's 2K2 pull-up and 3K3 current limiting
> resistors LED current will be less than 1 mA which is marginal
> for a PS2501/4N32 type opto that has a typical current transfer
> ratio between 300 and 500% (current gain of only 3 to 5).
>
> 73,
>
>     ... Joe, W4TV
>
>
> On 9/6/2012 11:07 AM, Greg wrote:
>> As Joe mentioned you will need to do the pull up resistor update for
>> this to work.
>>
>> I run a splitter cable off the ACCY port on the K3 with one side going
>> to my Quadra amp and the other side to the KK1L board.  Due to the
>> different impedences between the two it did not work (driving one by
>> itself was fine...but not both).  I had to add a buffer circuit
>> between the ACCY output and the band decoder input.  Once I did that
>> the KK1L board worked great with the K3 connected to the Quadra at the
>> same time.  I don't recall what IC I used but it was easy to
>> get...think I got it at radio shack.
>> If you are only going to be connected to the band decoder you should
>> not need the buffer.
>>
>> 73
>> Greg
>> AB7R
>>
>>
>> On 9/6/12, Joe Subich, W4TV <lists at subich.com> wrote:
>>>
>>> The PS2501-4 in the inputs of the KK1L band decoder are opto isolators.
>>> Pull up resistors will be required in the K3 in order to provide drive
>>> to the LEDs in the optos.
>>>
>>>> My KK1L board (built in 2006) seems to be loading down the K3 band
>>>> outputs.
>>>
>>> The K3 band data outputs are open drain - they can not be "loaded
>>> down" as they do not source voltage.  Note:  the KK1L design uses
>>> 3K3 Ohm series resistors to limit current to optos.  Depending on
>>> the sensitivity (current transfer ratio) of the PS2501-4 you may need
>>> to reduce the resistance of those resistors in order obtain enough
>>> current through the LED.
>>>
>>> 73,
>>>
>>>      ... Joe, W4TV
>>>
>>>
>>> On 9/6/2012 12:05 AM, Ethan Miller K8GU wrote:
>>>> Is anyone else running a K3 with a KK1L band decoder?  The K3 manual
>>>> states that "earlier K3s may require external pull-up resistors to 5
>>>> vdc."  Did you need to do this?  My KK1L board (built in 2006) seems
>>>> to be loading down the K3 band outputs.  Before I add the pull-up
>>>> resistors, I just want to make sure that this isn't a sign of
>>>> impending doom...
>>>>
>>>> Thanks and 73,
>>>>
>>>> --Ethan, K8GU/3.  (K3 S/N 6714, TS-930S S/N 5010245)
>>>>
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>>
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