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SP-1 

 16  

INITIATING SPEAKERPHONE CALLS: 
 

While the MC65118 IC makes provision for adding a DTMF tone dialer, the 
simplest and least expensive approach rate an ordinary telephone set as part of 
your Speakerphone installation. The average electronics buff is well aware that 
suitable phones are abundant at negligible cost, often with memory and other 
handy features. Simply connect the auxiliary phone and your SP1 to the phone 
line with a commonly-available dual-modular adapter, or use a dual wall jack, 
etc.  Use the auxiliary phone for dialing, incoming rings and situations where 
you prefer a handset. Enjoy the Speakerphone for efficient, hands-free 
communication. Be sure to hang up the auxiliary phone after turning on your 
SP1 Speakerphone.    
 

RINGER CIRCUITS: 

 
The SP1 does not include a ringer circuit for the simple reason that the average 
home, shop or office already has plenty of ringer noises whenever there are 
phone calls. If you are a telephone electronics enthusiast and really want a 
built-in ringer circuit, it is up to you to understand and comply with telephone 
company ringer circuit equivalency requirements.     
 

OPTIMIZING YOUR SPEAKERPHONE SET-UP:

 

 
There are three variables to be considered in any line-powered Speakerphone 
installation: 
 
1. Positioning of speaker in relation to the microphone. 
2. Your distance from the telephone switching complex which supplies line 

voltage. (If the voltage is marginal because you are on a distant point of the 
phone company "loop," supplementary battery power may be needed for this 
or any other Speakerphone. 

3. Basic "talk power" of the party on the other end. Let's consider the three 

details. First, if your Speakerphone works perfectly from the moment you set 
it up, then you are in great shape. Otherwise, consider the following:     

 
A. In general, some degree of acoustical separation must be provided 
between microphone and speaker. Put simply, they should not "point" at 
each other, or there will be some form of oscillation or erratic operation. 
Some experimenting may be needed. See also the section, Understanding 
Speakerphone Operation. 
 
B. Usually, telephone line voltage is sufficient for good SP1 performance. 
However, the available voltage is determined by the distance of your 
location from the central office and local factors. The easiest way to 
determine if a supplementary battery is needed is just to try it out. Please 
study the section Installing Optional Battery before making any type of 

Содержание SP1

Страница 1: ...he trick and doubles as a hands free intercom too Completely Hands free talk and listen at will Needs no battery runs off the phone line Sensitive pick up throughout the room Excellent speaker volume...

Страница 2: ...plifier RAMSEY AMATEUR RADIO KITS DDF1 Doppler Direction Finder HR Series HF All Mode Receivers QRP Series HF CW Transmitters VLF1 Low Frequency SWL Converter CPO3 Code Practice Oscillator QRP Power A...

Страница 3: ...S Introduction to the SP1 4 Parts list for the SP1 5 Parts layout diagram 6 Assembly instructions 7 Schematic diagram 12 Initial testing 15 Optimizing your set up 16 Understanding Speakerphones 17 Opt...

Страница 4: ...ild and to customize for your own needs and decor The Ramsey Speakerphone is designed to let you stay in charge of your time on a budget Think about the difference between that call you wish or plan t...

Страница 5: ...2 47K ohm yellow violet orange R7 R12 4 100K ohm brown black yellow R11 R15 R16 R17 1 68K ohm blue gray orange R5 SEMICONDUCTORS 1 MC65118 28 pin DIP speakerphone IC U1 1 LM386 8 pin DIP audio amplif...

Страница 6: ...SP 1 6 SP 1 PARTS LAYOUT DIAGRAM...

Страница 7: ...g out before soldering The part is then soldered securely to the board and the remaining lead length is clipped off SP1 ASSEMBLY INSTRUCTIONS We have a twofold strategy for the order of the following...

Страница 8: ...only two pins are actually used in the circuit 5 Examine the subminiature jack J1 supplied for speaker connection It fits into the PC board position easily Notice that the tab nearest to the edge of...

Страница 9: ...panel and therefore requires soldering the MK1 element s terminals to three short bare wires nipped from a previously installed component so that the three wires are at right angles to the MK1 lugs No...

Страница 10: ...r step and go back to it after you ve built up your scrap wire supply Jumpers act as electronic bridges carrying signals over PC board traces underneath 23 Near R3 install JMP11 24 Install JMP5 25 Ins...

Страница 11: ...RESS SUMMARY The schematic diagram makes it clear that building the kit consists largely of providing the supporting components for the many functions of the MC65118 IC Much of that has been done alre...

Страница 12: ...SP 1 12 SP1 SCHEMATIC DIAGRAM...

Страница 13: ...re that all 28 pins are visible on the solder side of the board Slightly bend the 4 outermost pins to lock the socket in place Make sure the socket is flush against the top of the board Solder all 28...

Страница 14: ...umper Wire from point A to point C near D3 2 Set both S1 and S2 to their out or off position Set the volume control to a mid range point 3 Next test the modular phone cord you intend to use with the S...

Страница 15: ...thing above checks out you re ready for your first Speakerphone conversation Ask someone to call you When you hear the ring on any other phone you can answer the call by pressing S1 You should be able...

Страница 16: ...ents OPTIMIZING YOUR SPEAKERPHONE SET UP There are three variables to be considered in any line powered Speakerphone installation 1 Positioning of speaker in relation to the microphone 2 Your distance...

Страница 17: ...our head or on a sketch pad Both stations must have speakers and sensitive microphones and be interconnected by two wires only and there can be no manual talk listen switches You must be able to turn...

Страница 18: ...ovides background noise monitors which make the circuit insensitive to room and line noise hybrid amplifiers for interfacing to Tip and Ring i e the phone line the microphone amplifier and other funct...

Страница 19: ...cted to the line or loop The phone line carries both audio energy AC and DC voltage T1 and T2 couple the audio signals to U1 s hybrid amplifiers pins 5 and 6 In telephone terminology hybrid is a circu...

Страница 20: ...nd C21 15 Supplies bias to volume control filtered by C24 16 Time constant for TX BNM set by R11 and C16 17 Input to TX level detector on mike speaker side 18 Output of TX level detector and input to...

Страница 21: ...one or more SP1 s you probably already have some handy switching ideas We ll leave those to your ingenuity To set up two SP1 s for hands free intercom service just do the following 1 Solder a jumper f...

Страница 22: ...SP 1 22 PARTS LAYOUT DIAGRAM SP1 SPEAKERPHONE KIT...

Страница 23: ...sistors you can pretty much be assured that the 1K ohm resistors are actually the missing 10 K parts Ramsey Electronics project kits are packed with pride in the USA If you believe we packed an incorr...

Страница 24: ...AL SOLDER POINTS 242 ESTIMATED ASSEMBLY TIME Beginner 4 0 hrs Intermediate 2 5 hrs Advanced 1 5 hrs REQUIRED TOOLS Soldering Iron WLC100 Thin Rosin Core Solder RTS12 Needle Nose Pliers MPP4 or RTS05 S...

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