PTT Circuit with Feedback to CTS??? - HomeBrew Forum at eHam.net

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PTT Circuit with Feedback to CTS???	Reply
by AD7KL on November 8, 2009	Mail this to a friend!
I am building a fairly simple opto isolated serial to PTT circuit for my marine radio. Putting it's SEND (PTT) pin to ground starts transmitting. When the operator uses the mike to transmit the radio also takes SEND to ground. I have seen a number of designs that use RTS to trigger PTT, but I have not seen any designs that also feedback the status of the radio on the CTS line. I was thinking of an opto isolator that goes back from the send pin to CTS (if either the RTS or Radio takes SEND to Ground, CTS is set). Am I missing something, or is there some reason not to do this? Thanks Evan p.s. For some reason can't attach a pdf here, but I can send the schematic for what I am thinking to any one interested. Once I figure out how to convert a grounded pin to a CTS signal through an opto isolator :) AD7KL

RE: PTT Circuit with Feedback to CTS???	Reply
by AD7KL on November 8, 2009	Mail this to a friend!
Ok, pdf of schematic is at http://www.diy-marine-electronics.com/circuits/pttwithcts.pdf , but I still haven't figured out where to get the power on the RS232 side of the opto when the Tx is keyed by the radio mike. I could switch the design to use a more expensive USB chip design, which supply's 5v from the computer, but I was hoping to do this with just the serial port. I can get 13.6 volts from the radio for the CTS, but then that negates the whole point of the opto.

RE: PTT Circuit with Feedback to CTS???	Reply
by N3OX on November 8, 2009	Mail this to a friend!
So you've got RTS and CTS tied up.... Maybe you can steal a little bit of power by keeping DTR or some other pin high.

RE: PTT Circuit with Feedback to CTS???	Reply
by AD7KL on November 8, 2009	Mail this to a friend!
Just updated the schematic (and uploaded) with DTR supplying voltage for the opto isolater. As I looked at the schematic though, it occured to me that the relay I put in to drive the CTS signal from the radio's send signal, would itself ground the signal, thereby taking send to ground? How do I avoid that?

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