PocketDial - PLANS

Circuit Description

Pocketdial consists of a Paralax BS2SX microcontroller interfaced to a POTS phone line through a 1:1 600 Ohm matching transformer and an LM386 Op Amp. The Op Amp is set at maximum gain to convert tones from the phone line to something resembling square waves, which the BS2SX counts as pulses to determine when it sees a "carrier."

While this is a hack, it works quite reliably and I have had no false positives so far in testing. I have had success with only one op amp though, so if you substitute a different one then an o-scope and BS2SX programmer may be necessary to troubleshoot carrier detection.

Click here: pocketdial-schem.jpg
(Sorry about it being hand drawn.)

BS2SX Software

Click here: pocketdial-10proto.zip
The BS2SX software is version 1.0 Prototype. It works fine, but does not yet include the password option, or the ability to dial the * or # signs. (0-9 and pause are supported.)