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|---10K Resistor---------------Thermistor--------| | ] | +5v ------ LM4040 (+2v048) ------ Thermistor --------------------- 10K resistor ---- GND | | ] | | ] |_______ADS1115--------------------------------A0--------A1
I did check the specification of the ADS115. It is 16 bits but one bit is the sign. (second complement format) In C this correspond to signed short.Question 2: Zero is definitely equal to zero volts (my ground), but what is the 65535 value? Does it equal the 2v048 I'm supply to the voltage dividers or is it the 5v I'm using to supply the ADS1115?
hmmm... so the point of setting the gain is just to let it know what the voltage reference should be? In which case it wouldn't actually amplify the signal prior to running it through the ADC so it doesn't matter if my supply voltage is 5v or 3v3?danjperron wrote:I did check the specification of the ADS115. It is 16 bits but one bit is the sign. (second complement format) In C this correspond to signed short.Question 2: Zero is definitely equal to zero volts (my ground), but what is the 65535 value? Does it equal the 2v048 I'm supply to the voltage dividers or is it the 5v I'm using to supply the ADS1115?
so if A0-A1 = 0 the digital value will be 0
= 2.5V the digital value will be 32767
= -2.5V the digital value will be -32767
This assuming that you set your gain to 2. The gain is the reference value to set your range.
Yeah, getting the schematic to display the way I wanted it to in a code block took a curious amount of finagling. The use of two thermistors was something that came up in a concurrent thread over on the adafruit customer service forum. Here's how it was explained to me.There is one question I do with your settings. Your schematic, which was really messing with my tablet but fine with my MacBook, contains 2 thermistors inside a bridge. Is the two thermistors will be on the same probe or you want to read a differential between them. If it is a differential I don't think it will work since the curve between voltage versus temperature is not linear. (This is a assumption since we don't have any clue about the thermistor curve you are using).
If both probe will measure the same temperature you increase the signal to noise but I.M.O. one sensor is enough.
It make all the calculation more difficult since you don't have a direct reading of the RT resistance, unless you read them individually I will just use one thermistor. Why 2 ?
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Let's say the thermistor changes 5% per degree C and lets assume we're 1 degree from the nominal temperature. The resistance of both thermistors will be 95% of 10k, or 9500 ohms. The voltage at the middle of the divider on the left will be slightly over 2.1v. The voltage at the middle of the divider on the right will be slightly less than 2v. That means the ADC will see a difference of 0.1v, which it can then translate into a temperature. No matter how the temperature changes, the voltages on the left and right will move in opposite directions.
The reason for so much accuracy is because my target accuracy is +/- 0.25 C so I'm using a higher degree of accuracy then I need because I know there will be plenty of factors that will drop that back down. Yes a current will warm the thermistor, but the whole point of higher accuracy thermistors is that they *should* be less affected by it. Also I've chosen resistors with a low temperature coefficient so they will cause less variation.What is the reason of so much accuracy. You know that passing a simple current on a thermistor will warm the device!
Also what is the range you want to use? This is important because that change the constant resistor value. 10K resistor is ok but if the thermistor range is between 1 and 10 ohm, it doesn't work.
[/quote]1- What is the thermistor specification?
2- What is the range in temperature you are looking for? And this also will tell you what is the Rt range.
3- A normal bridge for thermistor contains only one Thermistor. What is the advantage of using two? How to get rid of none linearity if your are using them in differential. Or is the way the thermistor parts is specify (contains two thermistors).
I have to beg forgiveness on this one, but I've been working on this for several days and my eyes are going cross looking at a giant wall of textdanjperron wrote:I did chat on a post about Steinhart-Hart equation.