If I understand your question correctly, you want to have the output of one RC PWM channel converted to a clean on-off TTL signal, correct?

That's correct.

 

Many years ago, I met a scan pulse should be change to the control signal as your needed, the difference is that your pulse isn't fixed.

I haven't try your PWM pulse yet, if you want then you can try it.
1N4148x1, Rx2 , Cap x3, calculating the values to match your need.

╨────╨────╨────
─┬─|>|───┬─./\/\/\,─┬─
..└./\/\/\/'─┤.............│
...............〒............〒
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Can you make a quick sketch, even on paint? I don't understand the top line of your picture.

 

Used a PICAXE 08M2 to do the job.

I hadn't touched such a low level language in a loooong time.
It was my first contact with a PICAXE system. Its features are absolutely hideous by today's standards. No negative numbers?!

But, hey, the program works and with the first compilation too!

 

Have you heard of the "picoswitch"? It takes an RC servo signal and drives a relay that could switch your TTL signal.

 

Huh! Never heard about it! It's exactly what I wanted.

BUT it costs several times as much as the PICAXE+74157 I used. Essentially I bought the hardware and built a similar system with 4 tied relays.

To be fair, the picoswitch allows large amperage, though.