[1000mp] Computer Interface

[Pitman, Zoltan, VF-NL]

Hello,
 
1, some modern notebooks have very current-limited COM-ports and these are not suitable to open an optocoupler enough to key your radio. I just measured my less-than-year-old HP nc6000: 
 
U [V]                I [mA]
5.94                  0
4.99                  5
3.5                    13 
 
2, The MP's PTT keying input's are commonized via diodes. If U key via the PTT connector you have 1 diode in series, if you key through the PACKET or RTTY connector there are two diodes in series. If you short the PTT input to ground with more than 50 ohms, it will not be enough to key the radio. 
 
Based on these you could do 3 things:
 
1, give up on the galvanical isolation (not a big issue here anyway) and use some switching FET like IRF-840, with like 1k in its gate in series. That will open up perfectly and can switch your shack heating, too. :)
 
2, If you stick to galvanical isolation pick up either an extreme high CTR optotransistor like TLP127 (and keep ur fingers crossed) or use FET outputted optoisolators like H11F2. 
 
3, use a small pnp silicon transistor (BC182, or BC107) to amplify the signal from the COM (to give ground to the optodiode) and hook up the other end of the optodiode to 13.8V via a suitable series resistor. You will find adequate 13.8 V supply on the back of your MP. 
 
Good luck, 
 
Zoli HA1AG
 
Ps: A healthy MP will drive 18 mA to ground when keyed to TX. 
 
 
 
> If you are using an Optocoupler you will need one with higher current
> transfer ratio for PTT. I measured over 10ma. of current that needed to be
> sinked when I checked my MP.
>
 73, Tom, W1TO
>
> ----- Original Message -----
> From: "Doug Rehman" <k4ddr at earthlink.net>
> To: "'All about Yaesu 1000mp'" <1000mp at mailman.qth.net>
> Sent: Monday, August 29, 2005 1:45 AM
> Subject: [1000mp] Computer Interface
>
> >I just finished building an interface for my Field for both CW and digital
> > modes. I used the circuit found at http://www.qsl.net/wm2u/interface.html
> > for both the CW key and the PTT. The CW key works perfectly from the
> > computer, but I am having a problem with the PTT line. The PTT line is
> > connected to Pin 3 of the "Packet" connector.
> >
> > When keyed by the computer, the PTT voltage drops from 13.4 volts to about
> > 2.7 volts- not enough to key the radio. If I parallel 50 ohms across the
> > opto isolator's output, it works like it is supposed to (the standby
> > voltage
> > on the PTT line drops to about .7 volts, but the radio isn't keyed until
> > the computer keys it).
> >
> > I've tried to use the CW key output for PTT, but it does the same thing so
> > I don't think it's a wiring or component issue.
> >
> > I've also checked the ground connection- no problem (.1mV difference
> > according to my DVM).
> >
> > It won't key the radio from the  PTT connector on the back either.
> >
> > I've used this exact same circuit before on a Kenwood TS-430S and TS-2000
> > without any problems.
> >
> > Any ideas? Anybody experienced this before?
> >
> > Hanks,
> > Doug
> > K4DDR
> >