Hi AAC people, Happy New Year.
I'm looking for some help on a project.
As you'll quick find out I'm nowhere knowledgeable in the field, but I'm trying by best to learn.
I'm trying to read from a sensing device that acts like a rheostat varying from 0 to 5 Ohms.
I'm not after very precise reading, if I could bet 6 or 7 bits of precision out of the full range, I'd consider myself happy.
The whole setup it running on 5v. I can either built it around a 1A or 0.5A voltage regulator. Obviously the smaller the better.
The microcontroller is a ATTiny13, for the record.
Concerning the rheostat I've been informed of its non linearity compared to a potentiometer, either I feed it with a current source or I get prepared to correct the non linearity on the microcode side.
Current Source or not?
What I have in stock is LM317. Used as a current source, it creates a significant voltage drop, 2v IIRC, which leaves me with not much voltage range to measure. Should I go for another current source setup ?
Or should I got without the current source? But then wouldn't my setup be using a lot more power?
Then how do I measure such a tiny voltage variation?
I made some computation, put in an voltage divider beside a 200 Ohms resistor.
Given I'm feeding the array a full 5v, I can expect the output voltage to vary from 5 to 4.85v at best, which is too short a range.
Concerning the 200 Ohms resistor, I'm afraid to go for lower values, I'm concerned about energy consumption/heat release.
Op-amps seems to be the answer, so I read about it.
Looks like the way to use them is with the negative feedback method, but then how do I read the resulting negative voltage with my micro controller?
Also I learned about instrument amplifiers, which seems to be what I need, I ordered a couple of INA126P (AD620 clone), hoping they would come handy. Was it a good idea?
I also came across the Wheatstone bridge, and especially its low resistance cousin, the Kelvin Bridge.
From what I understand they are designed to nullify the potential interference created by the wiring resistance. In my case, between the rheostat and the micro-controller, don't expect more than one foot of wire.
Do I need to dig into that or it's totally overkill for my particular application?
See, I did my homework, but unfortunately it's some shallow and theoretical knowledge.
I'm afraid it's a lot of questions packed into one post, feel free to correct me on any aspect of project. The only invariant it the sensor itself.
I'd appreciate some guidance on where I need to keep digging.
Thanks for reading.
I'm looking for some help on a project.
As you'll quick find out I'm nowhere knowledgeable in the field, but I'm trying by best to learn.
I'm trying to read from a sensing device that acts like a rheostat varying from 0 to 5 Ohms.
I'm not after very precise reading, if I could bet 6 or 7 bits of precision out of the full range, I'd consider myself happy.
The whole setup it running on 5v. I can either built it around a 1A or 0.5A voltage regulator. Obviously the smaller the better.
The microcontroller is a ATTiny13, for the record.
Concerning the rheostat I've been informed of its non linearity compared to a potentiometer, either I feed it with a current source or I get prepared to correct the non linearity on the microcode side.
Current Source or not?
What I have in stock is LM317. Used as a current source, it creates a significant voltage drop, 2v IIRC, which leaves me with not much voltage range to measure. Should I go for another current source setup ?
Or should I got without the current source? But then wouldn't my setup be using a lot more power?
Then how do I measure such a tiny voltage variation?
I made some computation, put in an voltage divider beside a 200 Ohms resistor.
Given I'm feeding the array a full 5v, I can expect the output voltage to vary from 5 to 4.85v at best, which is too short a range.
Concerning the 200 Ohms resistor, I'm afraid to go for lower values, I'm concerned about energy consumption/heat release.
Op-amps seems to be the answer, so I read about it.
Looks like the way to use them is with the negative feedback method, but then how do I read the resulting negative voltage with my micro controller?
Also I learned about instrument amplifiers, which seems to be what I need, I ordered a couple of INA126P (AD620 clone), hoping they would come handy. Was it a good idea?
I also came across the Wheatstone bridge, and especially its low resistance cousin, the Kelvin Bridge.
From what I understand they are designed to nullify the potential interference created by the wiring resistance. In my case, between the rheostat and the micro-controller, don't expect more than one foot of wire.
Do I need to dig into that or it's totally overkill for my particular application?
See, I did my homework, but unfortunately it's some shallow and theoretical knowledge.
I'm afraid it's a lot of questions packed into one post, feel free to correct me on any aspect of project. The only invariant it the sensor itself.
I'd appreciate some guidance on where I need to keep digging.
Thanks for reading.
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