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home automation, ESC, Embedded Systems Conference, microcontroller, MCU, earbud, coding

Small Module Allows New Products to Speak

With home automation assistance devices like Apple Siri and the Amazon Echo, non-intrusive voice synthesis devices are becoming common.

With home automation assistance devices like Apple Siri and the Amazon Echo, non-intrusive voice synthesis devices are becoming common. Specialized electronic hardware is used to artificially create a human voice for these home automation assistance devices.

The original speech synthesis was accomplish using as a computer dedicated to performing this function. A speech computer required massive amount of code to synthesis the natural sounds of the human voice.

Today, voice synthesis can simply be created using a small powerful electronics module with a variety of voices that can be programmed easily. The EMIC 2 Text to Speech Module, created by Joe Grand of Grand Idea Studios, can allow embedded developers and makers to add voice synthesis to their product designs.

The EMIC 2 TTS (Text to Speech) Module is a voice synthesizer that creates human sounding speech using converted strings of text. (Source: Parallax Inc.)
EMIC2 TTS Module Basics

The EMIC 2 Text-to-Speech (TTS) Module is a versatile, multi-language voice synthesizer capable of taking digital text and converting it into audible speech. It uses the DECtalk text to speech synthesizer engine, and the module is quite easy to wire to a microcontroller. The circuit schematic and breadboard wiring diagrams shown, illustrates the ease to adding the EMIC 2 TTS module to a new product design.

The EMIC 2 TTS module requires two digital pins from a microcontroller development platform (Arduino) for proper circuit interfacing. (Source: Don Wilcher)
Electrical wiring of the EMIC 2 TTS module to an Arduino. (Source: Don Wilcher)
EMIC 2 TTS Module’s Key Features

The EMIC2 TTS module provides a variety of features that makes it appealing to embedded applications such as robotics, healthcare, automotive, and industrial products. Some key features of the EMIC 2 TTS module include but are not limited to, high-quality speech synthesis, pre-defined voice styles, an onboard audio amplifier, and a single row header for electrical wiring. The EMIC 2 only requires a +5V DC, 30mA dc power supply. The operating temperature range of the EMIC 2 TTS module is -20C to 70C (-4F to 150F), making it suitable for typical environments. Dimensions of the EMIC 2 TTS module are 31.7 mm (W) x 38.1 mm (L) x 9.4 mm (H) which allows it to fit easily inside a small plastic hobby box.

The EMIC 2 TTS module small form factor (31.7 W x 38.1 L x 9.4 H mm) allows it to be packaged in a variety of new product designs. (Source: Parallax Inc.)
Another item to note about the EMIC 2 is the small audio jack soldered onto the pcb. This standard audio jack (size 1/8 inch [3.5 mm]) allows a typical earbud to be used with the module for individualize usage of the speech synthesis device. An example design application for this audio jack is the creation of a portable foreign language training tool. The earbuds will provide individual training to the foreign language learner without disturbing people in the room. The EMIC 2 TTS module has two speech synthesis languages available for English and Spanish.

Electrical Connections

There are only six electrical connections or pins required for wiring the EMIC 2 TTS module to an Arduino. The electrical connections consist of GND, 5V, SOUT, SIN, SP-, and SP+. The following descriptions below explain the operation of these 6 electrical connections.

          • Pin 1: GND – Device ground. Connect Arduino’s supply voltage ground (GND) to this pin.

          • Pin 2: 5V – Device power pin. Connect Arduino’s positive voltage (5V) to this pin.

          • Pin 3: SOUT – Device serial output to Arduino. A 5V TTL level interface, 9600 bps*, 8 data bits, no parity, 1 stop bit, non-inverted digital signal.

          • Pin 4: SIN – Device serial input from Arduino. A 3.3V to 5V TTL level interface, 9600 bps*, 8 data bits, no parity, 1 stop bit, non-inverted digital signal.

          • Pin 5: SP- - Device differential audio amplifier output, bridge-tied load configuration, negative side. Connect to 8ohm speaker directly.

          • Pin 6: SP+ - Device differential audio amplifier output, bridge-tied load configuration, positive side. Connect to 8ohm speaker directly.

A circuit schematic diagram for wiring an EMIC 2 TTS module to an Arduino. (Source: Don Wilcher)
DecTalk Speech Synthesizer Engine

The EMIC2 TTS Module uses a speech synthesizer called DecTalk. The DecTalk synthesizer can produce a natural-sounding voice based on the smallest memory IC footprint. The synthesizer can speak in multi-languages supporting U.S. English, Castilian, and Latin American Spanish. The 12-page document that Parallax Inc developed provides a wealth of information on maximizing the features of the EMIC 2 TTS Module. Below are examples from the Parallax document of how to set the internal feature/functions of the EMIC 2 using the DecTalk Speech Synthesizer and Arduino code.

Vx: Set the audio volume (db: Decibels)

The audio output volume of the EMIC 2 TTS module can be set in decibels from a range of -48dB (softest) to 18(loudest) using the following Arduino code. The default volume setting is 0.

 // Set volume to x: x= -48 to 18(max volume)
 while ( != ':');   // wait for ':' character

The speech output is sent to a bridged audio power amplifier. A Texas Instruments LM4864 bridged audio power amplifier is used to drive an 8ohm speaker with an amplification gain (AV) of 10.

A Texas Instruments LM4864 bridged power amplifier provides audio support for the EMIC 2 TTS module. (Source: Texas Instruments)
With this audio power amplifier IC and the DecTalk volume command, there is no need to add an amplifier circuit to the EMIC 2 TTS Module to obtain a suitable output level.

Nx: Select an EMIC speaking voice. There are nine voices to choose from as shown below.

0. Perfect Paul (Paulo)
1. Huge Harry (Francisco)
2. Beautiful Betty
3. Uppity Ursula
4. Doctor Dennis (Enrique)
5. Kit the Kid
6. Frail Frank
7. Rough Rita
8. Whispering Wendy (Beautriz)

The EMIC 2 TTS module’s voice can be change using the example Arduino code shown below.

// Set voice
while ( != ':');   // wait for ':' character

After uploading the modified Talking Logic Probe sketch with the DecTalk set voice command, Huge Harry (Francisco) will be heard through the 8ohm speaker.

Wx: Set the EMIC 2 TTS module’s speaking rate (words/minute)

Depending on the application, the speaking rate may need adjusting for clarity and understanding of the message. The range of values that are accepted by the EMIC 2 is 75(slowest) to 600(fastest). The default speaking rate value is set to 200. The example Arduino code to set the EMIC 2 TTS module’s rate is shown below.

        // Set speaking rate
       while ( != ':');   // wait for ':' character

Lx: Set the EMIC 2 TTS module’s language

The final DecTalk Speech Command is selecting a language for the EMIC2 TTS Module. The default language is English (0) but two other languages can be selected for the EMIC 2 as shown below.

          1. Castilian Spanish
          2. Latin Spanish
        // Set language
       while ( != ':');   // wait for ':' character

Additional information on pricing, application notes, design documentation and example programming code can be found at Parallax Inc’s website. Details on how to build a Talking Logic probe for testing digital and microcontroller circuits may be found in the Arduino Electronics Blueprints book published by Packt Publishing.

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Don Wilcher is a passionate teacher of electronics technology and an electrical engineer with 26 years of industrial experience. He’s worked on industrial robotics systems, automotive electronic modules/systems, and embedded wireless controls for small consumer appliances. He’s also a book author, writing DIY project books on electronics and robotics technologies.

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