[1000mp] PTT Interface

Thu, 26 Dec 2002 13:30:59 -0800

I tried to key my Timewave DSP 599zx using the PTT jack on the back panel -
it did not work either (I wanted to use the internal RTTY modem).  Sounds
like I should pick up the PTT from the front mic jack?  Tom W6EIJ

----- Original Message -----
From: jerry <[email protected]>
To: <[email protected]>
Sent: Thursday, December 26, 2002 6:53 AM
Subject: [1000mp] PTT Interface

> Hello Carl,
> I had the same problem with the PTT on my MP also.
> The MP PTT circuit on the front Mic input  requires a resistance 3900 ohms
to key the PTT, not much current required here,  so any opto interface
should work.
>
> BUT  .... the PTT inputs on the back of the rig are different,   they
require a resistance of 50 ohms or less.  To try to get it to work I tried
to lower the resistor on the RTS or DTR line side of the Opto circuit to
drive the Opto into mega saturation,  but that caused the RS-232 voltage on
the RTS or DTR line to drop from +12 to near zero causing nothing to work.
>
> My fix....
>
> On the cpu side
> Go from (RTS or DTR) thru a diode and 2.2k resistor to the base of a
2n2222,  emitter is ground,
> collector is going to the Opto thru a 470 ohm resistor then to +12 volts
 here I ran a wire from  a cd or hard drive connector in the cpu.)     All
this on the cpu side   for complete isolation.
>
> On the MP side.
> the ouput of the Opto to any PTT input on the back.
> The Opto can now be driven into saturation and not drop the RTS or DTR at
all as that line is only turning the 2n2222 on.
> This should work for any Opto, if not just lower the 470 ohm resistor in
the input collector a bit.
>
> Another note.......   I drive the FSK and CW key line in the MP  with the
TDX and DTR lines of the CPU with no problems using a standard Opto circuit,
just the PTT in the MP requires this added 2n2222 circuit
>
>
>
>
> Best regards.
>
> jerry    , N2UZ
> [email protected]
> 2002-12-26
>
>
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