Hi all, again. Thanks Mike, Peter, Bob for the comments on the ground-plane switching. I have revised the circuit, and removed the ground-switching MOSFET entirely. I had put it in there to isolate the RF components when at 5V, but, with the diode idea from Richard, I really don't need to worry about that. As for the drain current of the TX, I can leave it connected to the 3V cell as long as I power it down by pulling the PDN pin low. It has a 5nA Ipdn typically. Instead of having the FET control the ground plane, I now will control the PDN pin, with a P-MOSFET pulling it up to Vcc when required (and a weak pull-down otherwise). With that change, the two FETS and the diode on the cell isolate the PIC side of the circuit completely from the RF side. Programming the PIC can not possibly damage the TX components. In addition, I am no longer switching the ground-plane, and both RF and PIC components share a common ground. Fortunately, the RX side of the RF link is 5V tolerant.... ;-) Thanks again Rolf Michael Rigby-Jones wrote: > >> -----Original Message----- >> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] >> On Behalf Of Bob Blick >> Sent: 24 January 2007 20:11 >> To: Microcontroller discussion list - Public. >> Subject: Re: [PIC] Circuit Comment and Critique >> >> >> Hi Rolf, >> >> You are switching the ground for your RF circuit and antenna. >> Even if you added additional AC coupling to ground it still >> seems like a bad idea to me and something I would never do >> unless circumstances forced me, and then I'd test it both ways. >> >> > > That was one of the first things that I noticed and I agree it's asking for problems. For the cost of an extra transistor, a P channel MOSFET or even a cheap PNP bipolar switching the positive line with some decoupling after it would be a much more comfortable solution. > > Regards > > Mike > > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist