单片机用于测温,通常对A/D转换接口的转换速度要求不高,但要求有较高的精度和较低的价格。我们选用单片V/F转换器LM331和一块廉价的通用型四运放LM324,构成精度较高、价格低廉的远传测温T/F转换接口,其原理如图1所示。 (一)电路分析该接口电路由传感器驱动、电压放火和V/F转换等三部分组成。运放A_1、A_2(LM324N)以及晶体管T_1～T_4等组成一对恒流源,驱动三线制的热电阻R_t。这样可以消 Microcontroller for temperature measurement, usually on the A / D conversion interface conversion speed less demanding, but requires a higher accuracy and lower prices. We choose monolithic V / F converter LM331 and a cheap universal four operational amplifier LM324, constitute a high accuracy, low cost remote temperature T / F conversion interface, the principle shown in Figure 1. (A) Circuit Analysis The interface circuit consists of sensor-driven, voltage arson and V / F conversion composed of three parts. Op amp A_1, A_2 (LM324N) and transistors T_1 ~ T_4 and other components of a pair of constant current source, drive three-wire thermal resistance R_t. This can eliminate