Re: uBITX not T-41: Inversion of t/r signal
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Here is what I¡¯m using in the T41.? It¡¯s good to 250V and 2amps. ? 
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From: [email protected] < [email protected]> On Behalf Of Len, KD0RC Sent: Thursday, October 19, 2023 11:02 AM To: [email protected]Subject: Re: [AmateurRadioBuilders] uBITX not T-41: Inversion of t/r signal ? On Thu, Oct 19, 2023 at 09:25 AM, Mark Hatch wrote: The last item on my hardware TODO list is to provide a remote signal to trigger an amp or a RF switch. The signal that I need to expose is the T/R signal. The problem is that it goes positive on TX and grounds on RX. Sort of the opposite of what external devices expect.
Hi Mark,
Here is an inverting switch that I use on my TeensyMaestro project to key my rig.? This assumes keying a positive line by bringing it to ground.? This can be just about any NPN switching transistor.? I used a 2N3904 because I had some on hand.? Because this is inverting, it might work for you as-is.? If the polarity (HIGH vs LOW) is incorrect, you can use another GPIO pin (if you have a free one available) that is set the opposite of the existing RX/TX pin.???A better choice than my switching transistor would be an opto-isolator.? I believe it would be set up in a very similar way.
If you are out of GPIO pins, you could stack another transistor ahead of this one to invert the signal.? You would need a + V (3.5 or 5) through a current limiting resistor to the collector of the other transistor.
Any of you engineers see a flaw in what I am telling Mark?
73, Len, KD0RC
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