On Wed, Jan 16, 2013 at 12:50 PM, Carey Fisher w= rote: > 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 thin= k > the PTT is true low and I just use a 2N7000 to key the radio through this > 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? Makes sense, though I'm confused how a radio could also supply a bias voltage to an electret element. 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! 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. > We have adjustable TX level controls and treat the RCV audio as a speaker > output so we don't really pay attention to the radio specs. Also, on new > products we are using AGC on the RCV signal and it works great. Attached > is a schematic I found on the Internet and it works great. Ah, interesting idea. I like the idea of just putting AGC on the receive, then you never have to worry about it. I don't think I'll be there for version 1 of my project, but that's a cool idea for v2! > Also, don't even try to come up with a multipin connector. Just use the > Motorola adaptor. You'll be glad you did! I have an adapter, and since I'm testing with a two pin radio, this works out well. I'm talking to a local radio rental shop and I hope to get a few broken speaker mics (both two pin and multipin), so hopefully I will end up with working cables that natively serve both connectors. 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 .