| A telecommunications device for the deaf (TDD) is | | | | free of cost to deaf persons. |
| an electronic device for text communication via a | | | | Micon produced over 1,000 MCMs per month resulting |
| telephone line, used when one or more of the parties | | | | in approximately 50,000 MCMs being disseminated |
| has hearing or speech difficulties. Other names for | | | | into the deaf community. Before he left Micon in |
| TDD include TTY (telephone typewriter or | | | | 1980, Michael Cannon developed several computer |
| teletypewriter), textphone (Common in Europe) and | | | | compatible variations of the MCM and a portable, |
| minicom (United Kingdom). | | | | battery operated printing TDD, but they were never |
| About The typical TDD is a device about the size of | | | | as popular as the original MCM. Newer model TDDs |
| a small laptop computer with a QWERTY keyboard | | | | could communicate with selectable codes that allow |
| and small screen that uses light-emitting diodes or an | | | | communications at a higher bit rate on those models |
| LCD screen to display typed text electronically. In | | | | similarly equipped. |
| addition, TDDs commonly have a small spool of paper | | | | However, the lack of true computer interface |
| on which text is also printed — old | | | | functionality spelled the demise of the original TTY |
| versions of the device had only a printer and no | | | | and its clones. During the mid-1970s other so-called |
| screen. The text is transmitted live, via a telephone | | | | portable telephone devices were being cloned by |
| line, to a compatible device, i.e. one that uses a similar | | | | other companies, and this was the time period when |
| communication protocol. In certain countries there are | | | | the term "TDD" began being used largely by those |
| Telecommunications Relay Services, so that a deaf | | | | outside the deaf community. The deaf community, |
| person can communicate with a hearing person on an | | | | interestingly, does not usually use the term "TDD" |
| ordinary voice phone using a human relay operator. | | | | but instead prefers "TTY." Protocols There are many |
| There are also "carry-over" services, enabling people | | | | different textphone standards. The original standard |
| who can hear but cannot speak ("hearing | | | | used by TDDs is the Baudot code implemented |
| carry-over"), or people who cannot hear but are able | | | | asynchronously at either 45.5 or 50 baud, 1 start bit, |
| to speak ("voice carry-over") to use the telephone. | | | | 5 data bits, and 1.5 stop bits. Baudot is a common |
| History APCOM (Applied Communications) located in | | | | protocol in the US. In Europe, different states use |
| the San Francisco Bay area developed the acoustic | | | | different protocols. For example, V.21 is found in the |
| coupler, or modem. Couplers were cabled to TTYs | | | | UK and several Scandinavian countries. Other |
| enabling the Bell Telephone company standard "500 | | | | protocols used for text telephony are EDT, DTMF, |
| handset" to couple, or fit, into the rubber cups on the | | | | V.23, etc. |
| coupler, thus transmitting and receiving a unique set | | | | The TDD/TTY protocols are generally incompatible |
| of tones generated by the different corresponding | | | | with standard Hayes-compatible modems. In 1994 the |
| TTY keys. | | | | ITU approved the V.18 standard. V.18 is a dual |
| The entire configuration of teletype machine, acoustic | | | | standard. It is both an umbrella protocol that allows |
| coupler, and telephone set became known as the | | | | recognition and interoperability of some of the most |
| TTY. The acoustic coupler modem was the invention | | | | commonly used textphone protocols, as well as |
| of deaf physicist Robert Weitbrecht in 1964. The | | | | offering a native V.18 mode, which is an ASCII full- or |
| actual mechanism for TTY communications was | | | | half-duplex modulation method. |
| accomplished electromechanically through frequency | | | | Computers can, with appropriate software and |
| shift keying (FSK) allowing only one-way (simplex) | | | | modem, emulate a V.18 TDD. Some voice modems, |
| communication. In 1973 the MCM (Manual | | | | coupled with appropriate software, can now be |
| Communications Module), which was the world's first | | | | converted to TDD modems by using a |
| electronic portable TDD (Telephone Device for the | | | | software-based decoder for TDD tones. |
| Deaf) allowing two-way telecommunications, | | | | In the UK, a virtual V.18 network, called TextDirect, |
| premiered at the CAD (California Association of the | | | | exists as part of the Public Switched Telephone |
| Deaf) convention in Sacramento, California. | | | | Network, thereby offering interoperability between |
| Enlarge The battery-powered MCM was invented and | | | | textphones using different protocols. |
| designed by Michael Cannon in conjunction with | | | | The platform also offers additional functionality like |
| physicist Art Ogawa and deaf interpreter Kit Patrick | | | | call progress and status information in text and |
| Corson. It was manufactured by Michael Cannon's | | | | automatic invocation of a relay service for |
| company, Micon Industries, and initially marketed by | | | | speech-to-text calls. |
| Kit Corson's company, Silent Communications. In | | | | In addition to regular Baudot, the UltraTec company |
| order to be compatible with the existing TTY | | | | implements another protocol known as Enhanced |
| network, the MCM was designed around the five-bit | | | | TTY, which it calls "Turbo Code," in its products. |
| Baudot code established by the older TTY machines | | | | Turbo Code has some advantages over Baudot |
| instead of the ASCII code used by computers. The | | | | protocols, such as a higher data rate, full ASCII |
| MCM was an instant success with the deaf | | | | compliance, and full-duplex capability. However, Turbo |
| community despite the drawback of a $599 cost. | | | | Code is proprietary, and UltraTec only gives its |
| Within six months there were more MCMs in use by | | | | specifications to parties who are willing to license it. |
| the deaf and hearing impaired than TTY machines. | | | | Devices In addition to TDD, there are a number of |
| After a year Micon took over the marketing of the | | | | pieces of additional equipment that can be coupled to |
| MCM and subsequently concluded a deal with Pacific | | | | telephones to improve their utility. For those with |
| Bell (who coined the term "TDD") to purchase MCMs | | | | hearing difficulties the telephone ring and conversation |
| and rent them to deaf telephone subscribers for $30 | | | | sound level can be amplified or pitch adjusted, |
| per month. After Micon formed an alliance with | | | | ambient noise can also be filtered. The amplifier can |
| APCOM, Michael Cannon, Paul Conover (Micon), and | | | | be a simple addition or through an inductive coupler |
| Andrea Saks (APCOM) successfully petitioned the | | | | to interact with suitable hearing aids. The ring can also |
| California Public Utilities Commission (CPUC) resulting in | | | | be supplemented with extension bells or a visual call |
| a tariff that paid for TDD devices to be distributed | | | | indicator. |