一、工作原理简述1.电子铃电路HA881(Ⅲ)P/T 电话机的原理如图1所示。IC1(GF1240)等组成电子铃电路,其引脚功能如表1所示。平时叉簧开关 SA1闭合,接通电子铃电路,SA2断开拨号及通话电路,话机处于等待收铃状态。若呼叫本 First, a brief description of the working principle 1. Electronic bell circuit HA881 (Ⅲ) P / T telephone principle shown in Figure 1. IC1 (GF1240) composed of electronic bell circuit, the pin functions shown in Table 1. Usually switch hook switch SA1 closed, turn on the electronic bell circuit, SA2 disconnect the dial-up and call the circuit, the phone is waiting for the bell. If the call this