Microcontroller Efficiently Converts Sensor Voltage to Current Loop

摘要

WHEN TAKING MEASUREMENTS control circuits use some form of flip-flop that responds to a pushbutton switch or other control input. These all have volatile memory and default to an OFF condition if power is turned off, and sometimes that's even the preferred situation. However, if your application must remember what it was doing when power failed and resume from where it left off when power is restored, you may have a problem.The circuit in Figure I will deliver an output current from 4 to 20 mA for aninput voltage (V_(in)) from 0 to 5 V. PNP transistor Q1 (2N2907) is configured as a constant-current source; its emitter current and resistor value (R_e) are defined by the equation: