Is this the serial port or the parallel port on the computer that you are using? The serial port I always thought met RS-232 standards which swung from positive to negative. I used to use a RS232 to TTL logic converter back in the good old days to convert the signals but it was a commercial computer, not a PC. Measure the voltage out of the computer and see what you really have. A half volt swing is not enough. Gary - K7NEY
Chuck Kelsey wrote: > > > > > Sounds like the transistor isn't biased "on" all the way. Could be the > series resistor on the transistor base is too high a resistance value > or the transistor choice was bad. A 2N3904 or 2N2222 should work OK. > If you really want a "hard" low, use a power mosfet instead of the > transistor - like a 2N7000 or a VN10LP. In that case, the gate would > correspond to the base connection, the Source goes to ground, and the > Drain is your connection to the PTT on the radio. > > Chuck > WB2EDV > > ----- Original Message ----- > *From:* Vernon Densler <mailto:m...@highwayusa.com> > *To:* Repeater-Builder@yahoogroups.com > <mailto:Repeater-Builder@yahoogroups.com> > *Sent:* Saturday, April 18, 2009 6:05 PM > *Subject:* RE: [Repeater-Builder] Re: MASTR II PTT > > With the simple echolink interace which has a NPN transistor doing > the switching the voltage across the PTT line and ground is 7v > when the com port is not active and 6.5v when it’s active. So I > am only getting a ½ volt drop instead of a total short to ground. > Is it because the transistor can’t pull it down far enough? Will > a transistor with a higher power dissipation help? > > > > Thanks, > > Vern > >
