On Wed, Jan 16, 2013 at 11:15 PM, Josh Koffman wrote: > On Wed, Jan 16, 2013 at 12:50 PM, Carey Fisher > wrote: > > I sent drawings of the cable for the HT750 to your joshybear email > > address. Let me know if I should send them else where. As noted, I > think > > the PTT is true low and I just use a 2N7000 to key the radio through th= is > > cable. If it turns out to be true high, then add another 2N7000 as an > > inverter. The 2N7000s work well with logic signals (HC running off 5V)= .. > > Got them! So if your memory is correct, then pulling the TX Audio line > low through a 2.4K resistor triggers the transmitter, right? yes, well, my memory is not really relevant; the cable described by the drawing works. :-} > Makes > sense, though I'm confused how a radio could also supply a bias > voltage to an electret element. magic > Not a big deal in my case as I won't > have an element directly connected to the radio, but I'm a curious > guy! > remember the cat... > > I wonder if I can find a surface mount MOSFET to do this to cut down a > bit on board space. I'll let you know if I manage to figure something > out there. > 2N7002 is an SMT part that I use in place of a 2N7000. Don't forget to put a diode across the D-S of the FET (cathode to Drain) to protect it from any funky negative pulse from the radio PTT. May not be necessary but it's SOP for me. > > Josh > -- > --=20 Carey Fisher Chief Technical Officer New Communications Solutions, LLC 678-999-3956 careyfisher@ncsradio.com --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .