Hi i had a very basic question i cant find an answer to anywhere i looked. So Im building a vape with an arduino nano and i theres a way to find out the temperature of the wire(nickel) by knowing the resistance. So i want to calculate the resistance by program, but for that i need voltage and current. The problem is that i want to power the arduino and the vape with the same battery, and other forums say that since the arduino needs a value to "compare" the voltage reading with, if the battery is the same, then the arduino will always display a value of 1023(which makes sense). So my question is should i use a different battery to power the arduino? Or are there any components(or corcuits) for measuring current and voltage that can give me readings without the use of an extra battery? Thanks in advance.
What battery voltage?
If you know the gauge & length, look up the resistance in a [u]table[/u]. Or you can measure it with a multimeter but low-resistance measurements are not always accurate.... But it's probably more accurate than doing it with the Arduino. (I found a reference that says resistance doesn't change much with temperature.)
, but for that i need voltage and current.
Usually, current measurement is the tricky part. 
that since the arduino needs a value to "compare" the voltage reading with, if the battery is the same, then the arduino will always display a value of 1023(which makes sense).
You can use the optional [u]1.1V reference[/u] and a [u]voltave divider[/u] (2 resistors) to knock-down the battery voltage to less than 1.1V so it can be read (and scale the readings to take the 1.1V reference and voltage divider into account.)
Ok so i would use 2 18650s ( 2000mah and 7.4v in series). Lets say the gauge is 20 and i got 2 ft of nickel.
DVDdoug thank you for that but i forgot to include the fact that resistance would change. I will use a potentiometer as a knob to set a temperature on the screen, and the program should match that certain temp to the respective resistance and run a loop to make the chamber reach that resistance(and thus temp). Plus i want the program to also display the "current" temperature, so i need the arduino to read the resistance in real time.
I found this Precision LM4040 Voltage Reference Breakout - 2.048V and 4.096V : ID 2200 : $7.50 : Adafruit Industries, Unique & fun DIY electronics and kits Can i use this voltage sensor as a reference and hook it up to the same battery? Ive also seen actual voltage sensors, same thing, can i hook em up to the same batteries and still get voltage readings? Thanks
and i theres a way to find out the temperature of the wire(nickel) by knowing the resistance.
No their is no way to calculate the temperature from the resistance and voltage or current.
What you can calculate is the power dissipated in the resistor in watts, but that is not temperature as you need to know the thermal resistance of the coupling of your wire to the environment for that. You also need to know the temperature of the environment.
Thermal resistance is measured in degrees Centigrade per watt.
This page is about semiconductors and power but it applies equally to your situation, however you can't just look up the thermal resistance you need. http://www.thebox.myzen.co.uk/Tutorial/Power.html
My understanding is the Arduino chip has an internal reference voltage. That being the case you can use the same battery for both the Vape and Arduino.
I agree, you can obtain a temperature indication by knowing the resistance of the element.
Things to consider:
- Actually you can only measure a change in temperature knowing the V and I. To determine temperature you must also know the resistance at some known temperature(s).
- You have to measure the voltage and the current precisely.
- You might look a the nickel resistance and the tempco of the nickel (do you know the alloy) then determine how precise the voltage and current must be measured to get a meaningful reading.
Grumpy_Mike:
No their is no way to calculate the temperature from the resistance and voltage or current.
For a simple piece of resistance wire and reasonably large temperature range (hundreds of degrees) then I would not think it's too hard to do. Other ways are likely more accurate but for a small bit of wire boiling a liquid in a moving airstream, "accurate" is a relative term.
I agree, you can obtain a temperature indication by knowing the resistance of the element
Ok if you think you can calculate the temperature from simply the power how precisely do you do it if it is not what I said already. Otherwise you are just waffling.
We are talking about calculating it, not measuring it.
The calculation has nothing (mathematically) to do with power. It is simply the known relationship between temperature and resistance, of some alloys.
Alright sorry for the misunderstanding, i want to calculate RESISTANCE by using voltage and amperage that i get from reading the battery. At that point i would use a resistance-temperature table for nickel at 20 gauge (common to find online) to convert resistance to temp. I do not want to calculate heat, just resistance, and map the values of resistance with temperature so the arduino shows temp, but its actually dealing with resistance.
Thanks JohnRob, i think the arduino has only 1 pin for internal reference and that only kicks in for 1.1v or lower(am i wrong?). My only fear is that the readings wont be very precise at such low voltage level. Am i worrying too much? Would using an external voltage reference with the same battery work as well(adafruit has one for 5v so i would think that to be somewhat more precise)? Thanks and heres the link to the voltage reference again Precision LM4040 Voltage Reference Breakout - 2.048V and 4.096V : ID 2200 : $7.50 : Adafruit Industries, Unique & fun DIY electronics and kits
Watts dissipated in a load = voltage dropped across load in Volts times current flowing through it in Amps, but as GM said that wouldn't tell you much about temperature, if the wire was perfectly heat insulated so heat couldn't move away from it, it would melt pretty quick.
Well I only need to calculate resistance, temperature would be found on a table. I do not understand why I need the Watts dissipated. My question is much simpler than that, i wanna know if there is a way to measure voltage with the arduino hooked up to the same battery it is reading the voltage from. Is there any sensor or circuit that would allow me to set a specific voltage reference(not based on the battery), and read the battery voltage, only using 1 battery? Thank you.
You could use a voltage divider (2 resistors) and the Arduino's internal reference, answer the question in reply # 1.
Oh so you mean just reduce the voltage to less than 1.1v to use with the internal reference? I wanted to avoid that but that pretty much seems the only way for avoiding an extra battery, so Ill go with that (oh btw the battery will be 7.4v and 2000mah-->answer to the first reply). Thanks for all your replies, they have been super helpful.