sniper1rfa
Member
I've got a couple questions about analog inputs with the teensy.
I'm using a 10kohm potentiometer (BI tech P270, linear taper, polymer element) to measure the absolute position of a shaft. I'm getting what I feel is a surprising level of noise, with a DC bias, but I'm a mere MechE so I'm probably missing something.
The pot is connected VCC to ground. Power is being supplied from a 5VDC switching regulator on a pololu speed controller, through a linear regulator (MIC2937A-3.3WT). Analog resolution is set to 13 bits via analogReadRes. Analog reference is the default VCC.
First problem - I hooked an analog pin to an accurate voltage divider (two 10kohm .05% thin film resistors), and it's showing a fairly strong voltage bias.
EDIT:OK, this one was my fault. The pin I was using had the internal pullup on. That'll do it every time.
* does the VCC as a reference clamp at 3.333V, such that my 3.367V input is causing a bias?
* is there anything else that would cause such a bias?
Second problem - I'm getting variation of about 20 counts, which is about 0.25% error. Is that roughly the expected level of noise? Seems pretty consistent on both potentiometer lines and the voltage divider line.
I'm using a 10kohm potentiometer (BI tech P270, linear taper, polymer element) to measure the absolute position of a shaft. I'm getting what I feel is a surprising level of noise, with a DC bias, but I'm a mere MechE so I'm probably missing something.
The pot is connected VCC to ground. Power is being supplied from a 5VDC switching regulator on a pololu speed controller, through a linear regulator (MIC2937A-3.3WT). Analog resolution is set to 13 bits via analogReadRes. Analog reference is the default VCC.
First problem - I hooked an analog pin to an accurate voltage divider (two 10kohm .05% thin film resistors), and it's showing a fairly strong voltage bias.
EDIT:OK, this one was my fault. The pin I was using had the internal pullup on. That'll do it every time.
* does the VCC as a reference clamp at 3.333V, such that my 3.367V input is causing a bias?
* is there anything else that would cause such a bias?
Second problem - I'm getting variation of about 20 counts, which is about 0.25% error. Is that roughly the expected level of noise? Seems pretty consistent on both potentiometer lines and the voltage divider line.
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