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这里介绍一种制作简单的机内型家用电话防盗器。 其原理如图1所示,电话进线接在IN两端,电话机接在OUT两端。本机用户正常使用时,防盗器不起作用。当有人窃用本电话线时,即将窃用话机接在IN端之前时,防盗器即可发出干扰信号,使窃机无法使用。 工作原理:当用户未摘机时,线路上的电压通过B1桥的极性保护。在R1和R6上分压,使得V1导通,V2因失去基极电压而截止,V3不导通,由NE555时基电路组成的
Here to introduce a simple production of in-plane home phone alarm. The principle shown in Figure 1, the phone into the line at the IN ends, the phone is connected to the OUT ends. Local users normal use, anti-theft device does not work. When someone stole the telephone line, the phone is about to be stolen in front of IN, the anti-theft device can send out interference signals, so that the theft machine can not be used. How it works: When the user does not pick up the line, the voltage on the line through the B1 bridge polarity protection. Divide the voltage on R1 and R6, make V1 lead openly, V2 cut off because of losing base voltage, V3 does not lead, make up by NE555 time base circuit