A portable data terminal unit includes a data RAM for storing transaction data, and an acoustic coupler for transmitting the data stored in the data RAM to a computer installed in a business office. The portable data terminal unit has a battery for power supply purposes. The acoustic coupler is connected...http://www.google.com.tw/patents/US4905186?utm_source=gb-gplus-share專利 US4905186 - Portable data terminal
