Different Resistance Values for AD5293

Question

Hello, I have the following problem: I am testing two AD5293 digital potentiometers, and when cycling through all bit values to set the resistance, one of them behaves strangely. At some points, it shows out-of-range values, such as 180kΩ (which I assume is an open circuit). Then, it starts working normally, varying between approximately 50kΩ and 100Ω. However, when I try to set values manually, the readings are inconsistent. For example, at a setting of 0, it measures 166Ω; at 512, it measures 30kΩ; and at 1023, it measures 220Ω. Meanwhile, the other potentiometer, which behaves more consistently, gives these values at 0, it measures 37.3kΩ; At 512, it measures 20.5kΩ; At 1023, it measures 180Ω. Does anyone know what might be causing this? Is there a way to calibrate it, or could the potentiometer be damaged? This is the code i'm using:| #include const int slaveSelectPin = 5 ; // CS const int CLK = 18 ; const int SDO = 19 ; const int DIN = 23 ; void setup () { pinMode ( slaveSelectPin, OUTPUT ) ; SPI . begin () ; SPI . beginTransaction ( SPISettings ( 1000000 , MSBFIRST, SPI_MODE1 )) ; Serial . begin ( 115200 ) ; digitalWrite ( slaveSelectPin, LOW ) ; SPI . transfer ( 0x 18 ) ; SPI . transfer ( 0x 00 ) ; // Performance Mode digitalWrite ( slaveSelectPin, HIGH ) ; SPI . endTransaction () ; init_digiPot () ; } void loop () { /* digitalPotWrite(0); delay(4000); digitalPotWrite(512); delay(4000); digitalPotWrite(1023); delay(4000); */ unsigned int val; for ( val = 0 ; val <= 1023 ; val++ ) { digitalPotWrite ( val ) ; delay ( 100 ) ; } for ( val = 1023 ; val > 0 ; val-- ) { digitalPotWrite ( val ) ; delay ( 100 ) ; } } void init_digiPot () { SPI . beginTransaction ( SPISettings ( 1000000 , MSBFIRST, SPI_MODE1 )) ; digitalWrite ( slaveSelectPin, LOW ) ; SPI . transfer ( 0x 18 ) ; SPI . transfer ( 0x 02 ) ; // Wiper update digitalWrite ( slaveSelectPin, HIGH ) ; Serial . print ( "Setup: " ) ; Serial . println () ; SPI . endTransaction () ; } void digitalPotWrite ( unsigned int val) { SPI . beginTransaction ( SPISettings ( 1000000 , MSBFIRST, SPI_MODE1 )) ; digitalWrite ( slaveSelectPin, LOW ) ; byte highbyte = ( val >> 8 ) + 0x 04 ; //high wiper byte + command wiper update byte lowbyte = val & 0x FF ; SPI . transfer ( highbyte ) ; //send wiper data high byte SPI . transfer ( lowbyte ) ; //send wiper data low byte Serial . print ( "Val: " ) ; Serial . println (val ) ; digitalWrite ( slaveSelectPin, HIGH ) ; SPI . endTransaction () ; }

dendalisay · Answer

Hi, 
 The erratic readings I tjink were likely caused by the default write protection (C1 = 0) on the RDAC register. Disable it by sending Command 4 with bit C1 set to 1.This change lets the wiper update correctly. 
 Br, 
 Den

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Different Resistance Values for AD5293