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555 20-way answering device circuit

2015-01-30 05:48  
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555 20-way answering device circuit
As shown in the figure 11-30, the answering device circuit contains 20-way answering device switch and relevant relay control circuit, combined display digital board, audio circuit and timing circuit. After the host bringing up the question, the responder hears the sound of answering device, then he can press the answering switch, the digital dispaly board shows the answering group number. Both the positive and negative of dispaly board will dispaly, the side which is face to the responder and audience is composed of nine branches of 6.3V/0.15A bulbs( 1 word is shown by two branches); the side which is face to the host is made of LED. Each LED is in series with a 300Ω resistor, it is used to limit current. For example, the 13 group presses AN13 first, then D13, D23 turn on,J3, J 10, J11 pull in, the current passes through the paragraphes of a, b, c, d, g, h, the bulb turns on, it displays word 13 . Due to J3 pulls in, the answering power supply is cut off.