Shaft Encoder Drives Multiple XICOR Digitally Controlled Potentiontiom

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Shaft Encoder Drives Multiple XICOR Digitally Controlled Potentiontiom

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Suppose circuit design requires sprinkling around significant number control potentiometers, there only enough room front panel knob. aesthetic reasons other design considerations, only desired have control number seldom adjusted, essential control functions. shaft encoder, some simple circuitry, Xicor XDCPs provide versatile unique solution these types issues. Shaft angle encoders available cost from number manufacturers. Many these devices output signals phase quadrature degrees) with typically from 10,000 pulses available revolution. counting number transitions both phases, shaft angle control electronically resolved. using phases reference, direction that shaft turned also resolved. particular shaft encoder shown Figure capable encoding positions revolution, though other encoders selected with different angular resolutions. Each channel encoder four electrical cycles revolution. other words, electrical phase goes through degrees every degrees mechanical rotation. complete rotation shaft, there combined total level transitions transitions phase). Figure used Schmitt-trigger buffers phase channels Grayhill shaft encoder. gate (U6B) essentially adds these phases produce cycle revolution signal. along with delay network R1/C2 form one-shot which produces pulse every HIGH HIGH transition from U6B. There
Shaft Encoder Drives Multiple XICOR Digitally Controlled Potentiontiometers (XDCPs)
position pulses revolution, with only direction shaft rotation determined. This accomplished delay network R7/C4. shaft were being rotated constant velocity, motor, R7/C4 delay network would required since output would always defined direction- indicating state, going edge one-shot output formed U6C. Since shaft going rotated hand, erratic direction changes could take place, there exists possibility direction ambiguity. This solved delay network R7/C4 which stores direction that shaft going time that one-shot pulse produced. Notice that time constant direction delay much longer than one-shot time, ensuring that direction will valid falling edge increment pulse coming from output U6C. Because XDCPs should remember last setting power-down, required that HIGH before goes HIGH. This ensured timing networks consisting increment-invert network (CR2, R12, U10A, U10B, U10C), chip-select network (CR1, U6D). increment-invert circuit essentially increment pulse detector that holds U10B non-inverting state whenever increment pulse detected. non-invert period approximately times long increment pulse. This allows input selected XDCP return HIGH state after last falling pulse edge incremented pot. Since time constant chip-select network even longer, input will last return HIGH state after increment pulse, thereby ensuring that pots'current wiper setting stored. Close inspection reveals that U10B follower when increment pulse present
June, 2000
www.xicor.com
recently received, becomes inverter after increment pulse gone, thus returning HIGH state. 4-bit shift register formed which clocked pushbutton switch included Grayhill shaft encoder. shift register preset powerup with "1000," this selects first XDCP. Whenever pulse generated U6D, NANDed with output shift register U5and determines which will selected. Subsequent button pushes shaft encoder will select next sequence. length shift register
extended desired. Naturally, variety shift register schemes will work well shown, only problem being ability determine which active. Here, four LEDs serves simple index pointer indicate active pot. schematic shows application using four X9C103 type XDCPs. Also notice that terminals connected supply ground merely purpose this application, however these terminals connected voltage levels, long maximum exceeded.
Figure Shaft Encoder Driving Multiple XDCPs
June, 2000
www.xicor.com

Shaft Encoder Drives Multiple XICOR Digitally Controlled Potentiontiom

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