It would help if you would post a schematic showing how you are wiring it, and what is is you are wanting to do. When you said there is only 1/2 volt difference between on and off, it indicates that your transistor is wired incorrectly. Working from memory (and that is suspect!), you wouldn't need any resistors in the collector-emitter circuit, just a resistor in the base circuit for current limiting, and another from the base to the emitter for bias. Additionally, if you are switching a relay, you'd need a reverse biased diode across the relay coil (if there isn't one internally) to prevent damage to the transistor. I don't think you'd need a relay to switch PTT on a MastrII, but someone can correct me if I'm wrong. A typical repeater controller uses an open collector transistor to switch external devices, which is a fancy way of saying that the transistor acts like a switch, and can be used to switch PTT. When the transistor is turned on by the controller CPU, it simply pulls the PTT line to ground, thereby keying the transmitter. Without looking up the specs of a Com port, I couldn't say if it can be used for that, especially since I don't know which control signal you are using. Someone else mentioned using the printer port and it seems to me that it would be ideal for your application. Richard <http://www.n7tgb.net/> www.n7tgb.net
_____ From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Vernon Densler Sent: Saturday, April 18, 2009 3:06 PM To: Repeater-Builder@yahoogroups.com 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 its active. So I am only getting a ½ volt drop instead of a total short to ground. Is it because the transistor cant pull it down far enough? Will a transistor with a higher power dissipation help? Thanks, Vern From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Vernon Densler Sent: Friday, April 17, 2009 6:54 PM To: Repeater-Builder@yahoogroups.com Subject: RE: [Repeater-Builder] Re: MASTR II PTT OK. I am at my whits end here. The transistor wont bring the PTT line down enough to trigger. The optoisolator wont either. The mechanical relays cant be latched by the com port. The SSR latches but wont unlatch with DC. So do I run the SSR into an AC mechanical relay? Sounds like a serious Rube Goldberg way of doing it but it should work. There has to be another way though. It worked fine with the RC 1000 keying it so what does Ron have in that circuit that does the magic? Vern From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Ralph Mowery Sent: Friday, April 17, 2009 5:56 PM To: Repeater-Builder@yahoogroups.com Subject: RE: [Repeater-Builder] Re: MASTR II PTT You probably overlooked the simple thing. The PTT line is DC and once the SCR fires it will latch. If you had AC then the voltage goes to zero and the SCR unlatches. --- On Fri, 4/17/09, Vernon Densler <m...@highwayusa.com> wrote: From: Vernon Densler <m...@highwayusa.com> Subject: RE: [Repeater-Builder] Re: MASTR II PTT To: Repeater-Builder@yahoogroups.com Date: Friday, April 17, 2009, 4:35 PM I got a Solid State Relay and the com port will trigger it. (same thing I use to control my Christmas lights from my computer). However for some reason the PTT wont drop when the SSR shuts off. I know there is some voltage bleed on them but I cant figure out why it would stay grounded afterwards. Any suggestions on that one?
