Development Of The Full Electronic Active Adjustable Resistor

Resistor, as a basic electronic component, is widely applied to the electroniccircuit system, it is necessary to adjust the value of the resistor, how toaccomplish the automatic adjustment of resistance, wide range and high-resolution has become a technical problem in the circuit design. As the publiclyknown, traditional resistance box manually changes the resistance value, so it isso hard to automatically adjust the resistance. For mechanical potentiometer, it ischaracterized by low power, economical and practical. When it is connected tothe circuit, it can not determine the adjustment of the resistance, it has itsinherent life. And the digital potentiometer overcome these problems of themechanical potentiometers, and can achieve the automatic adjustment of theresistance, it has high accuracy, but the weakness is the single scale and lowresolution.According to Ohm’s law: R=U/I，the paper proposes a digital synthesismethod to adjust the value of the voltage by the program, so it accomplishes theequivalence function of the resistor. it can set the resistance and show the valueby the key and LCD. The internal circuit of the design consists of scaleconversion circuit, the gain setting circuit and the control circuit, the designchanges the scale by multiple-way switch, and shunts two multiple-way switchfor eliminating the on-resistance, The gain setting circuit adopts two pieces of12bit multiplying DAC chip AD5445to realize digital synthesis, at the same time,the design makes many resistors shunt to decrease the error which the singleresistance caused, so it improves the resolution and accuracy of the resistor. Thecontrol circuit uses the SCM to control the scale conversion, processes the datafrom the key input and sends it to DAC. This design achieves the continuousadjustment of resistance, its characteristic is that it has no relays, high resolution, good accuracy and multi-measuring range. When the resistance value range is0to1K, the resolution can reach to0.1, the accuracy is higher than0.05%.However, when the resistance value is more than1K, the accuracy is betterthan0.5%, the resistor, which uses the design method of the paper provided, hasa better application at the system in demanding to the size of the circuit.