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现在装有电话机的家庭已较为普遍,但装有门铃的家庭却不多。本文介绍一款利用现有电话机增加门铃功能的方法,它可以省去门铃,且门铃响声更加到位。电路原理如附图所示。B1为电源变压器,其次级12V抽头经二极管D半波整流、C滤波后,为继电器J提供电源。当按下门铃按钮QA时,继电器J吸合,其触点J1被切换至24V抽头(与电话进户线分开),电话机获得50Hz/24V交流电源。由于电话机正常呼叫振铃时,
Households with telephone sets are now more common, but there are not many families with door bells. This article describes a way to use the existing phone to increase the doorbell function, which can save the doorbell, and the doorbell sound more in place. Circuit principle as shown in the figure. B1 is the power transformer, the secondary 12V trough diode D half-wave rectifier, C filter, the relay J to provide power. When the doorbell button QA is pressed, the relay J is closed and its contact J1 is switched to the 24V tap (separate from the telephone line), and the telephone receives 50Hz / 24V AC power. As the normal phone ringing,