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Home Phone Network. ECE 345 Spring 1999 Sara Carroll, Jon Spychalski, Marc Gibbert Group #25 TA: Ajay Patel. Concept Overview. Integrate Available Features Low Production Cost Consumer Friendly Ease of installation Ease of use Convenient Size. Primary Features. Hardware-Only Features
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Home Phone Network ECE 345 Spring 1999 Sara Carroll, Jon Spychalski, Marc Gibbert Group #25 TA: Ajay Patel
Concept Overview • Integrate Available Features • Low Production Cost • Consumer Friendly • Ease of installation • Ease of use • Convenient Size
Primary Features • Hardware-Only Features • Standard Hold • Distinctive-Ring Hold • Intercom • Music-on-Hold • Reminder Ring
Secondary Features • Hardware / Software Features • Outgoing Call Blocking • Call Waiting while on Hold • Caller-ID while on-line • Integrate Caller-ID with Distinctive Ring • Remote Ringer • Ring-activated night light
DTMF Principles • Two frequencies combined to form one signal to prevent interference with speech • 7 frequencies used to generate all necessary tones • Used to signal digits dialed and line status from phone company • Oscillator, counter, decoder, D/A converter, and summing amp used to construct all tones for dialing
Research • Radio Shack’s Getting Started in Electronics • Radio Shack’s Mini Notebook - F. M. Mims III • Encyclopedia of Electronic Circuits Vol. 4 • Encyclopedia of Electronic Circuits Vol. 6 • Telephone Repair Illustrated - S. J. Bigelow • Understanding Telephone Electronics - S. J. Bigelow • Various ECE textbooks - 110,210,342, 330
Power Supply • 16V source is needed to drive phone while intercom is in use and to power amplifiers • Uses a DV-1215A wall transformer to simulate consumer conditions • Steps down wall power from 120 Vac to 16Vac • Uses a 78L05 voltage regulator to provide 5V to the IC’s
Reminder Ring • Provides a ring after hold has been enabled for approximately 80 sec. • Once enabled, a capacitor begins charging until it reaches the variable reference voltage when the ringer circuitry is enabled • Person on hold hears a ring back tone
Intercom System • Allows user to talk to another user on internal phone network without disabling outside phone network • User hears “call waiting” tone in the event of an incoming call while using intercom • When # # 9 is entered, SW2 switches to allow the 16 V source to power the speech network
Standard and Selective Hold • Logic initiated by DTMF receiver and Bin/Dec converter • All sequences begin with the depression of two #’s in series • A third # initiates standard hold and activates music on hold as well as switching outside line to hold circuit • A number 1-4 initiates selective hold and ringing begins immediately
Music-on-Hold • Electrically isolated to prevent accidental connection of power lines to phone lines • When caller on hold, SW1 turned off thereby forcing audio signal through amplifier onto phone line • During 80sec-hold ring-back SW1 turns on thus temporarily disabling Music-on-Hold until ring is complete
Line Status Indicator • Indicates whether the phone is off-hook • Used to enable reset inhibit and ring back reminder • Has protection against accidental initiation by ringer circuitry
Ringer System • Ring clock maintains standard 6 second cycle of telephone ringing • Specified ring selected through hold setup logic • Ring oscillator generates 25Hz square-wave
Ringer System (continued) • Filtered to generate 25 Hz sine wave and then amplified to 90Vac to ring house phone • Ring back oscillator generates an audible 600Hz square wave gated at 25 Hz • Tone then injected onto outside phone line through line driver (ring back signal)
Circuit Setup • Placed on a bread board of 60 in² for ease of testing and debugging • Power supply, Music-on-Hold, Ringer circuitry, and circuits usingTRANS2 were placed near the edge for easy access • Initial estimates show it could be placed on a printed circuit board of 7” X 7” X 3” • Low frequency circuitry negates the need for RF interference protective shielding
Testing • Power supply was tested initially in the lab because it can be tested without powering the other circuitry • Power supply was checked to insure it was outputting 5V and 16V • Functionality of all features was then checked in the lab and in a consumer environment
Parameter Variation • The Reminder Ring time can be varied by changing the resistors of the voltage divider input of the comparator • The gain of the audio output for the music-on-hold circuitry can be changed by varying the feedback and input resistor values • Can also vary diode array to generate other ring patterns, or vary the output frequency of ring-back oscillator to produce different tones
Secondary Features • Secondary features would utilize a MC68332 microcontroller and caller-id decoder • Initialization code is included in Appendix A • Potential problems include impractical call-blocker and distinctive ring due to arrival of caller-id information after 1st ring.
Cost Analysis • Labor Costs: • Hrs/engineer = 119 • Engineers = 3 • Expense Factor 2.5 • Total Labor Costs = $22,312.50 • Parts Costs • $70.00 • Overall Costs • Total Cost = Labor Cost + Parts Cost = $22,312.50 + $70.00 = $22,379.50 • Initial Cost Estimate • Initial Cost estimate = $33,816.00
Product Installation and Use • Connect power supply, telephone line and audio input
Conclusions • Accomplished primary goals under budget • Set foundations for further development of secondary features • Gained knowledge and experience working with telephone networks, DTMF technology and other advanced hardware components. • Were able to create a low-cost, feasible and marketable electronic device for consumer use.
