I'm working on a calibration project that will use a digital potentiometer acting as a shunt resistor for a piezoresistive accelerometer. I'm trying to confirm the values of resistance for the potentiometer (DS1803), but the results have been very sporadic and even just setting the DMM to read resistance while the device is powered on seems to have lots of variance.
If I directly measure the resistance at max (theoretically 100kΩ) it looks to realistically be around 92.5kΩ. This is not consistent though because as I sit here and write this, the resistance is varying to sitting around 90.1kΩ to 89.5kΩ to 91.4kΩ and occasionally jumping down to 70kΩ. Through lots of testing, 92.5kΩ seems to be the most consistent result for the max resistance. There does seem to be a very small voltage(~0.05mV) present when reading these resistances, so I'm thinking maybe that is why this is not working properly, but even that reading is not always present.
Ideally, I would like to run through all the resistances and record them to get a baseline for what to expect in the resistances, but doing this several times resulted in resistance variance of around 500Ω-5100Ω in the larger resistance range (92.5kΩ-59kΩ) with an average resistance range variance of 2260Ω. As I did more recording sessions this range of variance seemed to decrease though, such that the average variance is decreased to 249Ω if I remove my first two trials (of 7 total) from the calculation. I thought the problem might've been the DMM, but I tried a different DMM as well but it will also sometimes vary wildly in measurement.
Notes on Circuit:
All I have set up right now is pretty simple. I've got the address pins for I2C tied to ground, +5V on VCC (pin 16), ground to ground (pin 8), I2C pins (SDA/SCL) tied to a communication device with some diodes to clean up the signal and some resistors because the communication device said to have resistors. This is currently breadboarded and not soldered. I'm measuring the resistance across pins 14 and 12 (Digipot 0's Hi and Wiper respectively) with no voltage directly connected to any of the Digipot pins.
Is there a better way to determine these resistance values? I've thought about just forgoing full range resistance measurements and just using the maximum resistance to calculate the step value and working with calculated values for what the resistance should be there, but I'd rather have some more assurance that the digipot is operating properly than that.
DMM: Tekpower TP9605BT (Tried to grab the datasheet/manual here but it looks like the site is down right now)
Digipot: DS1803-100 Courtesy of Tony Stewart
I2C: Adafruit FT232H Breakout Board for I2C Communication and as a temporary power supply (Via PC USB). Couldn't find a direct datasheet for this, adafruit has a guide but not a datasheet I could readily find.
FT232H - The chip that the Adafruit breakout board uses