> 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 <li...@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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