LM35 temp sesnor equation for arduino uno which connected to matlab GUI

Question

Hi I'm new in matlab GUI

I am trying to create an axes plot the temperature which comes from LM35 through arduino uno to matlab

I used the following code to read the analog voltage, readVoltage(a,0) I get a values about 0.28 - 0.30 but I don't know exactly what this values exactly means is it the the real temperature/100 or what? I know there is an ADC inside arduino converts the input voltage to another range (0-1023) when I use analogRead() on the arduino side. Does it also work here or not? I confused about this thing when I should assume it is 0-1023 or directly get the reading.

Answer 1

The arduino ADC reads a voltage and outputs a number according to

1. the reference voltage
2. the bit width of the ADC

in this case I suppose that you are using the 5V reference and 10 bit mode, so

Vmeasured = NumberFromADC * 5V / 1024

Now, according to the LM35 datasheet the output voltage is

Vout = 10mV/°C * T

inverting the equation:

T = Vout / (10mV/°C) = NumberFromADC * 5V / 1024 / (10mV/°C) = NumberFromADC * 500 / 1024

(of course expressed in °C)

BTW I suggest you to change the voltage reference to an internal one, since the 5V are not stable and precise enough to have a good measuring system. More info here .

And, of course, if you change the reference voltage you will need to change the equation since the reference itself will not be 5V anymore.