Generate CID/CIDCW Analog Signals:  12/07/00 EDN-Design Ideas / (added 5/02) / A high-speed µP can generate CID (caller-ID) and CIDCW (caller-ID-on-call- waiting) analog signals (Figure 1). CID data transmits at 1200 baud FSK between the first and second 20-Hz ring of an incoming call. CIDCW uses a CAS (CPE Alert Signal) dual tone, which consists of 2130 and 2750 Hz to initiate the FSK data transfer. You can produce these analog signals using software-generated PWM (pulse-width-modulated) outputs from a high-speed µP, such as an Atmel AVR or Scenix SX. You create these PWM outputs using a constant-sampling frequency, and you select this frequency so that small, repetitive integer-number samples define the desired output. The 11.0592-MHz µP clock frequency and single-instruction cycle time are the same for IC1. The design produces the 1200-baud FSK marking frequency of 1200 Hz by using 22 cycles of a constant-sampling frequency of 11.0592 MHz/419. The design produces the 2200-Hz spacing frequency by using 12 cycles of the same sampling frequency. At each sample, the µP produces a PWM TTL output proportional to the analog....

Greek telecard reader:  The circuit based on AT90S2313 AVR microcontroller from Atmel, programmed with telecard.hex and telecard.eep .  The converter from + - 12V of RS232 to TTL and from TTL to + - 12V is MAX232. When you build the circuit ( I think its very simple ), connect the reader with RS232 port of the PC, run the Hyper terminal software ( start – programs - accessories – communications – Hyper terminal ) and set the baud rate to 19200 bps 8 none 1.... (added 4/05)

Ground Rules for High Speed Circuits:  AN-214 - Analog Devices Application Notes  (app note added 6/06)Layout and Wiring Are Critical in Video Converter Circuits.

HamComm Interface:  (circuit / schematic added 6/05)

HamComm modem interface:  (circuit / schematic added 6/05)

Having secrecy in parallel telephones:  (electronic circuit added 10/05)

Hold Function for Telephone:  ASCII format (added 8/03)

Home Made PBX/PABX:  (circuit / design added 8/03)

Improving the Accuracy of Optical Transceiver Extinction Ratio Measurements - (AN 1550-9):  Agilent Application Note   (added 6/06)

Improving the Performance of a High Speed PBX Backplane:  National Semiconductor - Application Note   (app note added 2/06)

Infrared Head Phones:  Using this low-cost project1-can reproduce audio from TV without disturbing others. In place of a pair of wires, it uses invisible infrared light to transmit audio signals from TV to headphones. FAIR WARNING -- THIS SITE HAS ANNOYING POP UP ADS. (added 5/02)

Isolated indicator signals telephone line's status:  6/8/06  EDN - Design Ideas  /  (added 10/06)  Micropowered circuit shows off-hook phone.

Isolated Telephone Interface:  This circuit allows you to record audio from a Telephone line into a tape recorder or computer soundcard. Most of the parts for this circuit can be scrounged from an old modem, with some work, it is possible to rewire the modem circuitry and use the old modem case. (added 5/02)

Journal of Internet Test Methodologies:  Agilent Application Note   (app note added 6/06)

KD2BD Pacsat Modem:  (circuit / schematic added 6/05)

Line busy indicator:  This circuit flashes an LED if the phone line is in use or is ringing. It is powered by the phone line, and it uses so little current that several of them could be used on the same line without interference. When first connected, let the circuit charge on an idle line for a couple minutes before expecting it to work. A high-brightness LED is recommended. (added 1/08)

Link Telephone Intercom Every Home Should Have One!:  The Link circuitry is simple and efficient, employing just two ICs, half a dozen transistors, and a handful of garden variety components. It all runs on 12 volts and is easily assembled. You can have your own home intercom between the kitchen, the garage, the rumpus room and at your poolside ‘barby’ and all for less than $100! The “Link” intercom has been designed in such a way that you can buy parts for it ‘off the shelf’ at just about any decent electronics retail chain. It uses old pulse dial handsets and replaces the AC bell set with a 9 volt DC buzzer. The whole circuit runs from a 12 volt regulated DC supply and is suitable for short term battery operation (eg: ‘Gel Cell’). It is suitable for radio field days and sporting events (providing you can scrounge enough 4 wire cable) and may find a place in pre-schools, old folk’s homes, boy scout/girl guide halls, churches, kids’ tree houses/fortresses, or maybe even more serious uses such as small offices, factories...   (added 10/05)

Low-Cost PCO Billing Meter:  (electronic Circuit / Schematic added 10/04)

Measuring Jitter in Digital Systems (AN 1448-1):  Agilent Application Note   (added 6/06)

Message Waiting Flasher:  This circuit starts flashing a neon light when the phone rings and continues flashing it until the phone is picked up to remind you to check your voice-mail. The flashing neon light drives a voltage doubler (Q2) which keeps it flashing. Q1 ensures that the flashing is stopped when the phone is picked up.  Designed by Andrew R. Morris  (added 09/05)

Mobile Cellphone Charger:  (electronic Circuit / Schematic added 10/04)

Mobile Phone Battery Charger:  (electronic Circuit / Schematic added 10/04)

Modem-access adapter reduces interference:  07/22/99 EDN Design Ideas  / (added 2/06) 

Multipurpose Circuit for telephone:  (electronic circuit added 10/05)

Multipurpose Circuit for Telephones:  This add-on device for telephones can be connected in parallel to the telephone instrument. The circuit provides audio-visual indication of on-hook, off-hook, and ringing modes. It can also be used to connect the telephone to a cid (caller identification device) through a relay and also to indicate tapping or misuse of telephone lines by sounding a buzzer. (added 3/03)

Music On-Hold for Telephones:  (electronic Circuit / Schematic added 10/04)

NCDS Interface Schematic for Nokia 3110 8110 8110i:  (circuit / design added 8/03)

Nine-Line Telephone Sharer:  (electronic Circuit / Schematic added 10/04)