INTRODUCTION The DCI2 ( D TMF C ontroller I nterface) is designed to meet the needs of the home automation experimenter. The easy hookup interface and simple operation lends itself well to a variety of applications. The DCI2 can be configured by the user to operate in several different modes to meet your specific requirements. A coded binary set of outputs provides either a latched or non-latched data output mode. A special configuration is also provided to interface to the Ramsey Electronics DVMS, ( D igital V oice M essage S ystem), to allow messages to be selected and played using DTMF tones. All configurations may be operated in a secure or non-secure mode.
A set of 16 active low outputs are also provided. These operate independently of the DCI2 configuration and provide continuous monitoring of the input signal. Any valid DTMF tone activates a corresponding output for as long as the tone is present. The DCI2 continually monitors your phone line, or just about any other audio source, listening for any Dual Tone Multi Frequency (DTMF) signals. Another name for these signals is Touch Tones. When the DCI2 detects a valid signal it decodes it and performs the appropriate actions. We’ll now explain in more detail these actions and how the DCI2 operates.
CIRCUIT DESCRIPTION Take a look at the DCI2C’s Schematic Diagram as we walk through the circuit description. We will start with the DTMF audio input and work our way through to the power supply section. The Input The DTMF audio input uses a standard RJ-11 modular phone jack (J6 - Phone Line Monitor In) for easy interfacing with your phone line or other audio source (a direct audio pinout for J6 is shown in the “WIRING AND CUSTOM APPLICATION SUGGESTIONS”) section of this manual. The input circuitry near the phone jack allows the DCI2 to continually monitor the audio signal and detect any DTMF data that comes in so it can be decoded.
The audio sniffer formed by C14, C15, R8, R9, and R10 presents a high impedance to the input signal. This allows connection to the phone line without making it think the phone is off-hook so it will not capture the line and does not interfere with the normal use of your phones. Protection diodes D2 and D3 limit the incoming signal to +/- 0.7 V so that potentially damaging voltages like the 90 Vp-p ‘Ring’ signal do not damage the decoder IC. Capacitor C11 blocks any DC potential that may be present from reaching U3’s input on pin 2 thru R3. DCI2 4