注册参加Maxim在TechOnline举办的在线研讨会 (English only) Companies usually purchase one type of telephone for all employees. But this means that every ringer has the same sound and when one phone rings, a dozen people pause and look at their telephones. Equally annoying is the absence of a visual message indicator, so anyone who suspects they may have a message must lift the handset and listen for a special message tone. By placing a circuit in series with the telephone (Figure 1), you can customize a phone ringer without modifying the phone. The heart of the ringer is a chip-recorder IC (U5) capable of playing up to 10 seconds of telephone-quality recorded sound. A high-efficiency step-down converter (U1) allows the circuitry to operate from a supply voltage of 5V to 14V. For larger image Figure 1. This circuit plays up to 10 seconds of recorded sound in place of the ring from a telephone. It also indicates when someone has called. An opto-coupler and associated front-end circuitry monitor the line, sensing when the line receives a high-voltage ringer signal (Figure 2). Zener diodes D4 and D5 prevent the on-hook voltage from activating the opto-coupler. Comparator U3 latches LED D6 "on" when a call is received, and a pushbutton switch (SW1) clears the comparator. Figure 2. The ringer signal of a typical telephone exceeds 200VP-P (vertical scale is 50V/div). The circuit shown in Figure 3 records up to 10 seconds of sound in the chip recorder's proprietary multi-level EEPROM. A switch-mode, Class D audio amplifier (U6) maintains high efficiency while delivering adequate power to an 8Ω speaker (even a PC speaker will work). Figure 3. Using the EEPROM internal to U5 in Figure 1, this circuit records up to 10 seconds of sound. A similar version of this article appeared in the July 25, 2002 issue of EDN magazine. 相关型号   APP 1187: Sep 06, 2002 MAX1684 低噪声、14V输入、1A、PWM降压型转换器 完整的数据资料 (PDF, 304kB) 免费样品 自动更新 需要自动接收最新发布的应用笔记吗？请订阅EE-Mail™ (English only)。 我们期待您的反馈！ 喜欢？不喜欢？有待改善？或为我们提供建议？请与我们联系 — 我们将根据您的意见或建议改善我们的工作。 网页评价或提供建议   下载，PDF格式 (45kB)  AN1187, AN 1187, APP1187, Appnote1187, Appnote 1187