GSM/GPRS Module with TTS

Description

The SIM900TTS module is a SIM900 with built-in speech synthesis, obtained by raising the internal memory from 64 to 128 Mb and by revising the firmware of the on-board microcontroller that runs it. After the firmware update released to let the SIM900 read DTMF tones directly, without the need for external decoders, SIMCom has now produced and loaded into recent SIM900TTS units a firmware release that implements TTS, that is, that reads out the words it receives through specific AT commands. The voice used for the synthesis can be “tuned” by setting its volume, its pitch and its speaking rate.
The SIM900TTS has the same functions as the SIM900: it is a quad-band GSM/GPRS/EDGE cellular engine able to handle voice calls and SMS, to read a keypad and to recognise DTMF tones. It includes a TCP/IP stack and is controlled through AT commands. Its very small size (24 x 24 x 3 mm) makes it possible to develop very compact devices such as trackers, GSM telephone diallers, remote control units, remote alarms and so on. The module is surface mount (SMT), so it needs no connector.

The technology that lets our telephone dialler speak is genuine speech synthesis, which in its general form can pronounce words that the device receives as text: TTS in fact stands for Text To Speech, literally “from text to speech”. So a computer or another device sends the words to be spoken and the TTS device turns them into speech; they can be sent as ASCII characters along a serial data channel of one kind or another, or in some other form.
In our case the technology has been implemented in a SIMCom quad-band cellular module, designated SIM900TTS, which is essentially the well-known SIM900 we have used in many remote control and GSM telephone dialler projects, but with TTS built in. The module can both speak the words it receives as text inside an SMS or a serial command, and send the matching audio down the line during a phone call.
In the dialler, TTS takes the place of the block that would otherwise have been a digital voice recorder. In this new dialler, instead, we have a true speech synthesiser built into the cellular module, which lets us change the words or phrases assigned to each event, either remotely by SMS or locally by connecting a PC to the communication port. In the SIM900TTS the Text To Speech function can be used in two directions: to let the person at the other end of a phone call hear the audio matching a written text, or to convert the text of an SMS into speech through a loudspeaker connected to the module output. In our dialler we use only the first mode, but the importance of the second should not be forgotten: it lets us build devices such as SMS readers, useful both for finding out what a text message says without reading it and handling the phone (handy for anyone who has to work hands-free) and for blind users, who can in this way listen to the SMS or to a text their own phone has received or is downloading from the Internet.

• GPRS multi-slot class 10/8
• GPRS mobile station class B
• Compliant to GSM phase 2/2+
  – Class 4 (2 W @850/ 900 MHz)
  – Class 1 (1 W @ 1800/1900 MHz)