本刊95年第1期第16页介绍了一种同线电话监视器的制作,笔者认真读后觉得有些看法值得一提。首先是图2的同线电话监视器是通过稳压二极管DW进行稳压后,为集成块IC提供工作电源的。其稳压用限流电阻R1取值为4.7K。稳压值为5.1V。从此可以计算出,平时电话机挂机时,流过R1的电流I≈(48—5.1-0.7×3)伏÷4.7千欧,即约为9毫安。这是一部电话监视器所耗的电流。如果同线上有两部以上的话机装有这种监视器,则所需的总电流,起码在十多毫安以上。这不仅邮电局不允许,甚至可能造成外面的电话无 The first issue of 95, No. 1, page 16 describes a production of the same telephone line monitor, the author felt that after some serious reading is worth mentioning. The first is the same line telephone monitor in Figure 2 is stabilized by the regulator diode DW, to provide power for the integrated block IC. The regulator with a current limiting resistor R1 value of 4.7K. Regulated value of 5.1V. From this it can be calculated, usually when the phone hang up, the current flowing through R1 I ≈ (48-5.1-0.7 × 3) vol ÷ 4.7 kilo-ohms, which is about 9 mA. This is the current consumed by a phone monitor. If there are more than two phones on the same line with this monitor, the total current requirement is at least a dozen milliamperes. Not only is this not allowed by the post office, it may even result in no external calls