I'm trying to build a thermometer using the LM335 temperature sensor and arduino. Reading this datasheet page 4, there are many ways to build a circuit around the sensor but only the first one is simple enough for me to kind of understand, but looking at for example the "Isolated Temperature Sensor" at page 5 makes me dizzy.
My question is what's the difference between these two application schematics? Is the first circuit good enough for a thermometer project or it's just a proof that the sensor works(like the blink example)?
Also in some schematics the sensor has two pins and is drawn as a diode symbole, while in others it has three pins and drawn like a chip. Mine has three pins. At the beginning of the datasheet it says that the sensor is essentially a zener diode:
Operating as a 2-terminal zener, the LM135 has a breakdown voltage directly proportional to...
So I'm assuming the sensor is "modeled" as a zener diode in those schematics? But then which pin is which?
Its not NECESSARY but you can use the pot on the adj pin to calibrate the sensor (1 point calibration)
By calibrating the output to read correctly at one temperature the output at all temperatures is correct. Nominally the output is calibrated at 10 mV/K.
Calibrate for 2.982V at 25°C
Yeah it definitely is. For someone who doesn't understand electronics well, it can be overwhelming and also hard to filter out the useful information from the datasheet.
Nominally the output is calibrated at 10 mV/K.
I don't understand this part...
Calibrate for 2.982V at 25°C
But I think I can calibrate it only based on this information.
It's amazing, I thought it would be much harder at first. Thank you!
I want to adjust the output voltage so that zero degree cesius will result in near zero volt output.
In a circuit replicated from the "Calibrated Sensor" schematic, I'm using a 500 ohm resistor and a 5K ohm potentiometer.
The problem is no matter where I position the potentiometer, the measured output voltage doesn't change at all. It changes initially just as long as I'm turning the knob but as soon as I stop it again, the multimeter shows the exact same number.
Thank you! this answers the exact same question that I wanted to ask next. Actually I've tried a couple of times to read sensors before and have always had this problem of offset and range/scale.
The op amp is an MCP6002
I think I only have 741's right now but I'm not sure. In that case do you recommend using it? I'm asking because it doesn't have a good reputation but I thought maybe it's good enough for this project?
Also I honestly just skimmed through your article but I am going to read it and try to apply it to my project.
I initally thought I have this sensor but after checking again it turned out it's LM335, and I'm just trying to build something with the parts I already have.
Really? That's an ancient design.
Many schematics will indeed tell you to use a 741, but what it really means: "just about any common cheap general purpose opamp will do just fine here. We don't really care which part. It's an opamp." Often those schematics don't even provide the dual supply a 741 expects.
MCP6002 is an inexpensive rail to rail OpAmp.
The LM324 and LM358 are also common and cheap.
Those will run fine on a single 5V supply.
I know but I'm just a beginner hobbyist so sometimes I just buy things hoping they'll be useful someday.
but what it really means: "just about any common cheap general purpose opamp will do just fine here. We don't really care which part. It's an opamp."
Thanks for the tip! I didn't know that and always thought I have to use that specific chip or I have to redesign the whole schematic which I don't know how to do.
MCP6002 is an inexpensive rail to rail OpAmp.
The LM324 and LM358 are also common and cheap.
Those will run fine on a single 5V supply.
I'm gonna have to buy a couple of those then. I remember multiple occasions when I was trying to replicate a schematic with op amps not knowing about the concept of rail to rail and I was frustrated that It doesn't work!
