Circuit Lake

Electronic Project and Circuit Collection

Stealth Telephone Screener

01/09/2011 Category: Microcontroller, PIC, Project

The project allows you to determine whether or not the caller is an actual person. If not, it hangs up without ever disturbing the user. But, when the caller is real human then its built-in ringer will give alert to user. Telephone screener is very useful to avoid automated telemarketing call in the middle of dinner, just to find only silence at the other end of the line. The hardware is based on microcontroller PIC16F872 and plugs into an ordinary phone line. While, its firmware is written in assembler and compiled using Microchip MPASM 3.20.

telephone caller detector

Richard Wotiz, the designer, explained how telephone screener works. Firstly, the screener will answer incoming call and playing back a brief greeting (such as “Hello”), then waiting for a response. If there is no sound for 5 seconds, or if there is a continuous response that lasts longer than ten seconds, then it hangs up. Otherwise, it plays a second greeting (such as “Just a minute”), and activates the ringer, while playing a ringing signal to the caller. Once the user has picked up any phone on the same line, the Screener stops ringing and releases the line.

Automatic Telephone Screener
Project Detail and Documentation