Telephone answering machine design example

Document created by Fernanda Servin Employee on Apr 12, 2016Last modified by Fernanda Servin Employee on Apr 18, 2016
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The Telephone Answering Machine Design Example is a sophisticated telephone answering machine that provides everything commercial devices offer and more. Noteworthy features include improved voice quality and increased storage capacity over commercial machines. Additionally, Internet connectivity enables convenient messaging in the form of SMS messages or e-mails from anywhere in the world. Virtual answering machines can be set up for four different users. A user-friendly interface makes learning how to use this device and taking advantage of its many special features easy for anyone, regardless of their electronics savvy. The highly efficient system is designed around an LPC2138 microcontroller, which features an ARM7 RISC processor. Built with a small handful of components, the Telephone Answering Machine Design Example is cost-effective. The thoughtful inclusion of an external flash memory card and well-chosen algorithms for nearly unlimited storage capacity of crystal-clear messages contribute to the success of the design.

Block Diagram



  • Telephone Answering Machine


Below are recommended microcontrollers for use in implementing a telephone answering machine.

Comparison Table

ProductPinsOn-Chip FlashOn-Chip RAMComments
LPC213864512KB32KBBase microcontroller used in the design example.
LPC213664256KB32KBA lower-cost microcontroller with the same amount of on-chip RAM but with only half the on-chip flash memory.
LPC214664256KB32KB + 8KBAn upgraded microcontroller with a USB interface. USB could be used instead of Ethernet to connect to a PC if Internet functionality is not desired.

More Information



Working Prototype


Circuit Blocks


Answer Flow

Telephone Answering Machine

  • Schematics
  • Example Code
  • Bill of Materials



This design example shows possible hardware and software techniques used to implement the design. It is imperative that the viewer use sound engineering judgment in determining the fitness of this design example for any particular application. This design example may include information from 3rd parties and/or information which may require further licensing or otherwise. Additional hardware or software design may be required. NXP Semiconductors does not support or warrant this information for any purpose other than an informational design example.