| Variable resistor is one of the most common electronic components and the most commonly used electronic components, but more for the exchange properties.Variable resistors commonly used has three pins, two for the fixed point and a sliding point, they also known as the potentiometer; other variable resistors has only two pins, a fixed point and a sliding point.They all have one thing in common: they are all through the change between sliding and fixed position to change the resistance value, which has the characteristics of small volume, wide application, convenient adjustment.But there is a common drawback: it is difficult to adjust the value for the specific resistance,and the resistance is not easy to read.So program controlled variable resistor is in order to overcome the difficulties and developed.Programmable DC variable resistor through the buttons can directly regulate resistance to their desired values, in the liquid crystal display screen can directly read out the resistance value,we do not need to measure the resistance value by any other means, and through the program control of resistance has high precision, not easy to change and other advantages.The core of the design is a voltage-controlled current source, in the variable resistor input terminal add a fixed voltage value, if the voltage-controlled current source of constant voltage, the output current is constant, the resistance value of the output will not change.Changing the input voltage of voltage-controlled current source, you can change the output resistance value easily, and the input voltage of voltage-controlled current source is changed by single chip microcomputer,that is the controlled variable resistor.Programmable DC precision variable resistor of this design has only one input terminal, internal ground, a DC characteristic, the circuit can only be used at the end of the voltage dividing resistor in series with the other, than a single use, however, it has a higher precision. |
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