Using Several LM335 with ARDUINO2009

Hi all.

I would like to monitor temperature in an oven to check if temperature is homogeneous in the hot volume.

I have bought 5 LM335A sensors and an Arduino2009.

With one LM335A, the wiring is easy : On the Arduino 5V pin, i wire a 1kOhms resistor then the LM335A positive, then the LM335A negative pin, then the ground. The LM335+ pin is on the analog1 entry. => Everything looks fine, temperature seems OK.

I add the 5 LM335A in parrallel on the 5V Arduino pin and : 1. Intensities are high (as the total resistor is low). 2. The signal of the LM335A is constant even if I heat them. I tried to compute an equivalent resistance and adjust the resistor values (set them higher) but although the tension changes, the temperature value is wrong.

I guess there is an electronic problem behind this, but I can not figure out what is the cause.

Does it means something for you ? Anyone faced this problem ? In other words, is it stupid to try to wire 5 LM335A in parrallel on the 5V power supply ? Do I need to have separate 5V power supply ? Is it possible to use 5 lm335A on an Arduino2009 ? If no, why ?

Thanks for your help.

Regards.

Jérémy

In other words, is it stupid to try to wire 5 LM335A in parrallel on the 5V power supply ? No it is OK

Do I need to have separate 5V power supply ? No Is it possible to use 5 lm335A Yes

I am not sure what you are doing wrong. Each sensor needs to be wired to it's own analogue input and there needs to be a separate resistor for each sensor.

Each sensor needs its own resistor and its own analog input pin. I'm not sure what your set up is without a diagram, but I think you've directly connected the sensors in parallel, so they'll be fighting each other and the coldest one will win.

Thanks for your help.

Here is what I did :

-------------------------------------------------- (+)5V(-)–
I I I I I I
R R R R R I
I I I I I I
I I I I I I
(+)-> A1 (+)->A2 (+)->A3(+)->A4 (+)->A5 I
LM LM LM LM LM I
(-) (-) (-) (-) (-) I
I I I I I I

I tried with several resistors. Currently, I am using R=2.2KOhms but I also tried with higher resistors, the main thing is to keep the intensity in every branches in the LM335 range (0.4mA<i<5mA).

The adjustement pin is not wired as I am referring to the first example in LM335 documentation (basic temperature sensor).

If any suggestions…

Jeremy

I forgot to add what I read on the Arduino :

1;3.25; 2;3.25; 3;3.26; 4;3.26; 5;3.27;

The first column is the sensor ID The second is the analog value through the ADC 10 bits : // Analog Read tp_Analog=analogRead(_pin); tp_Analog=tp_Analog/(2^5);

As // Conversion in °C tp_Analog=tp_Analog*100-273.15; The temperatures are around 55° and I do not live in the sahara ! :) Regards.

Jérémy

Ive got the same exact problem. i cant seem to get any good readings from the 4 lm335AZ i have…
did you get it working in the end?

i did read that because the voltage swing from 0C to 100C is small that we should use an op amp. so i tried that with no luck either.

Regards, Sean

Do the readings you get from the sensors change when you grip them between thumb an forefinger? If not you have misidentified the pins on the device. Remember the data sheet shows the view from the bottom of the device.

Hi Ioniser,

I did not found the solution to my problem. I think I have well understood the pins configuration(i.e. bottom view).

Finally, I did the conclusion that arduino power supply was limited to supply 5 or 6 analog sensors as I had sometimes problems to supply sensors with Arduino through USB hub.

All I can say is that I swapped to DS18B20 digital temperature sensors. As it works with one wire bus, you only need one digital pin for ALL sensors which is much more convenient when working with several types of sensors. Nevertheless, do not use them in parasite power mode if you need 1 Hz or higher. I can explain you if you're interested.

The bad bad point is the price (around 5 to 7 dollars as I remember).

If you find a solution with LM335, please let me know. If any questions on DS18B20, I may help you.

Good luck.

Jérémy