On Sun, Jan 6, 2013 at 11:34 PM, Carey Fisher wr= ote: > Anyway, let me know how I can help. Hi Carey, Ok, first radio specific help that I need. The radio that I most commonly run across is the Motorola HT750. I don't own any myself, but I plan on building this and testing it with some Motorola radios that are capable of using the same speaker mic. While the HT750 uses a multipin connector, there is an adapter that lets you use a GP300 style two pin speaker-mic with it. Eventually I will likely make a multipin cable, but for the moment I'll be using the two pin connection. In any case, I'm looking for a few bits of info. First off, I'm curious if Motorola ever lists the specifications for the audio ports on their devices (ie impedance, level, etc). Second, how do you guys normally trigger the PTT on radios such as this? From what I've found, it appears that the radio is triggered by an impedance on the mic line. Here's the schematic of their speaker-mic: http://www.batlabs.com/images/gpspkmk.gif . I also found a vaguely promising schematic for the test set cable that shows perhaps a different way of triggering PTT: http://hamradio.lakki.iki.fi/new/Software/radioprogramming/Motorola/Pinouts= /gp300svc.gif .. I haven't had time to try it out yet. Any pointers? I'll need a way of triggering it from a logic level signal. Thank you! Josh --=20 A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools. -Douglas Adams --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .