PIC16F877A as a modem?

John P · Joined: 17 Sep 2003 Posts: 331

I've got this idea for a data communication system running over a cordless phone (because they're incredibly cheap and come with a recharging system all bult in). In order to minimize the components in the handset, it occurred to me that maybe using the PIC's A/D capability and some kind of digital-to-frequency output, I might be able to do this with a "software modem" running on the PIC itself, rather than having an external modem and controlling that. I think I could live with a modest baud rate, say 1200, but it has to be bidirectional. I'd like to use a standard modem protocol, but I suppose a custom design would also work; the data gets demodulated at the base station, not sent over a phone line, so there's no need to interact with any other equipment.

Has anyone done this? Got code to give away?

ak6dn · Joined: 08 Jan 2006 Posts: 23 Location: Saratoga, CA USA

Guest · Posted: Thu Feb 09, 2006 5:40 am

I think I have to agree.
On the transmit, it is just about possible to generate the required tones using the PWM. On receive, tone detection, with a reasonable success rate, would be very hard. A simple detector IC, like the NE567, could make it work, but a basic modem IC, is just about the same money as such an IC, and would also be more reliable. Realistically, it could be done with such a decoder, but 'why bother'.

Best Wishes