[Elecraft] TX inhibit question

[Joe Subich, W4TV]

> Pin 7 is connected to the front panel microcontroller with a series
> 220 ohm resistor. The microcontroller on the front panel is a 5
> volt part so I wouldn't apply any voltages greater than 5 volts (or
> the maximum logic high voltage.)

The alternative would be to install a 4.7K - 10K resistor between the
external 13.8V inhibit source and the K3 inhibit output (as N0SS did
in the Quadra/K3 cable).  The resistor would limit the current into
the microcontroller to a safe level in all cases.  Another option is
to install a 5.1V zener diode across the inhibit input (or output of
the sequencer with the appropriate current limiting resistor) to keep
the voltage on the K3 "inhibit input" from exceeding 5V.

73,

    ... Joe, W4TV


On 9/9/2011 10:48 AM, Cady, Fred wrote:
> Hello Erwin,
> Pin 7 is connected to the front panel microcontroller with a series 220 ohm resistor. The microcontroller on the front panel is a 5 volt part so I wouldn't apply any voltages greater than 5 volts (or the maximum logic high voltage.)
>
> 73,
> Fred
> KE7X
>
> Fred Cady
> fcady at ieee dot org
> "The Elecraft K3: Design, Configuration and Operation"
> www.ke7x.com
>
> (Lulu has 20% discount for the K3 book until midnight 9/9 - SEPTEMBER305 - and 15% through 9/30 - AWESOME305. See www.ke7x.com.)
>
>
>> -----Original Message-----
>> From: elecraft-bounces at mailman.qth.net [mailto:elecraft-
>> bounces at mailman.qth.net] On Behalf Of DK5EW
>> Sent: Friday, September 09, 2011 8:22 AM
>> To: Elecraft at mailman.qth.net
>> Subject: [Elecraft] TX inhibit question
>>
>> Hi all,
>> since 05.September I'm proud owner of a K3 # 5776.
>> Now I work trough the manual from side 1 to end to understand function.
>>
>> As I use a sequencer to protect my LNA's I will use also the RX inhibit
>> function.
>> The sequencer will provides 13VDC  in RX mode to the ACC connector  at
>> pin 7.
>> I understand I have to set CONFIG: TX INH to high. But can I use 13VDC
>> to that pin 7 or better
>> what's the maximum voltage can be there at pin 7?
>>
>> --
>> best regards
>> Erwin/DK5EW
>>
>>
>>
>>
>>
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