Myalarm V-LED1 Instrukcja Użytkownika Pobierz pdf (Strona 3)

Issue 194 September 2006

CIRCUIT CELLAR

www.circuitcellar.com

was a good decision by the designers.

In most applications, the module sim-

ply would be connected to the serial

outputs of a microcontroller, but it

makes level translation circuitry nec-

essary to interface to the MC13192-

EVB. I used a Linear Technologies

LT1081 level translator chip for this

job. Its function is similar to the popu-

lar MAX232 family and all of its deriv-

atives, any of which would have been

well suited for the job. I just happened

to have an LT1081 on hand.

The Emic has an onboard audio

amplifier that can power external

speakers up to 300 mW, which is suffi-

cient volume for connecting to an

unamplified speaker. It also has a sep-

arate analog output, which is connect-

ed to the telephone interface circuitry

to send audio signals over the tele-

phone line. An analog input allows the

Emic to amplify audio from the phone

line, which is useful for debugging

purposes.

Sending ASCII text commands to

the serial input at 2,400 bps controls

the Emic. Commands are available to

convert text to speech, set the volume

level, set the speed and pitch of the

synthesized speech, check the Emic

version, turn on the audio input, and

open a Help menu. You can also store,

delete, and recall abbreviations.

I used only the reset and text-to-

speech conversion commands for this

project. To reset, simply send a reset;

command to the module and wait for

the busy line to go inactive. To con-

vert text to speech, send the text to be

spoken to the module preceded by the

“say=” command and follow up with a

semicolon to finish the command. For

example, to say “hello,” send the

say=hello; command.

The Emic’s busy line is connected

to a logic input on the MC13192-EVB.

This allows the software to wait for

the Emic to finish one command

before starting the next. Note that all

of the logic external to the MC13192-

EVB is 5-V logic. The MC13192-EVB

uses 3-V logic, so a ULN2003 IC con-

sisting of seven open-collector transis-

tors with integrated base resistors is

used for logic level translation for all

of the logic inputs to the MC13192-

EVB. The internal pull-ups on the

MC13192-EVB’s logic lines are

enabled in the software to ensure a

logic high when the open collector

transistor is off.

The audio generated by the Emic

module is injected into the phone line

through a telephone direct access

arrangement circuit built around a

Cermetek Microelectronics CH1837

DAA module that provides some

surge and protection circuitry, isola-

tion, a hybrid two- to four-wire con-

verter that separates the transmitted

and received audio, ring indication,

and hook control. External to the

DAA is more robust line protection

circuitry and EMI suppression circuit-

ry that includes capacitors from tip

and ring to ground to bypass EMI,

fuses for surge protection, and a tran-

sient voltage suppression diode across

the tip and ring. The transmit connec-

tions go to the Emic speech module.

The receive line is routed to the

DTMF detection

circuit. The ring indi-

cator and off hook control lines are con-

Figure 1

—The main components in the base unit are a Freescale MC13192-EVB, an Emic text-to-speech module, and a Cermetek CH1837A direct access arrangement.

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