Multiple Sensors and Power Drain

I’m a software guy, but dabbling in the electronics aspect using the Arduino and love it…

I’ve got multiple TMP36 sensors hooked up via Category 5e cable (less than 1 foot) and have that hooked up to the 5V, Ground and Analog Sensor ports on the arduino. I’m getting voltages from the sensors back at 0.98v, etc - which seems wrong to me.

What I eventually want to do is have 1 Arduino and Cat 5 cable running to each of the sensors (100’ maximum for each sensor).

Does this sound crazy - do I need an Analog to Digital Encoder to get reliable signals back to the Arduino?

Zack

Does this sound crazy

yes 100' is a long way for an analogue sensor, it will not work because the cable will attenuate the signal.

do I need an Analog to Digital Encoder to get reliable signals back to the Arduino?

That is one way but then how do you get those digital signals back to the arduino? That is quite tricky too, and it involves a lot of wires.

A better way would be to put it to a voltage to frequency converter at the remote end and send that through a driver buffer. Then have a receiving buffer at the other end and have the arduino measure the frequency of this signal.

Other things to consider is wireless transmission.

Thanks Mike - that sounds like an interesting approach. I was thinking about a wireless solution, but trying to minimize the costs.

Would having a purely digital temperature sensor (instead of analog) help my situation as is? Or would I still need to amplify the signal back to the arduino?

Would having a purely digital temperature sensor (instead of analog) help my situation as is?

Yes it would. However, it would depend on what type of digital output you had as to what amplification you would need. As I said 100' is a long way for a logic signal. Those sorts of distances are more suited to things like RS232.

When it is the arduino what do you want to do with it then? Pass it up to a PC? If that is the case have it all at one end and communicate back to the PC with RS232. If you don't have a RS232 port you can always use a USB / RS232 adaptor for the last foot.

I didn't want to involve a computer at all so I've got it all hooked up via an Ethernet shield. All that works. I'm just leary of the results. Sometimes the data is inconsistant when I hookup another sensor (I guess it is possible a bad sensor exists on Analog Sensor #3)

For example, I have the following results from a TMP36 (polled every second)

Analog Sensor 0 Shows: 0.74v 24.22C 75.59F 0.74v 23.73C 74.71F ...

but

Analog Sensor 3 Shows: 1.54v 106.25C 223.25F 1.54v 103.32C 217.98F ...

You can see from the following image url how I've got it all rigged up (that's a 6' RJ-45 cable) and it is correctly dumping results to a test web server. I'd like to eventually change this to 100' and dump the results every 60 seconds). I don't show sensor #3 hooked up

http://imagebin.ca/view/NeMh-vs.html

In the data I report above...

a 6' RJ-45 cable is on Sensor #0 a 1' RJ-45 cable is on Sensor #3

I guess that's my analog attenuation error, but suprising that Sensor #0 reports correct, but a shorter cable reports wrong.

I guess I could always hookup a 25' or 100' to see what happens.

Thanks for all your help and information...

Zack

Interesting, but I guess makes sense....Replaced the 1' with a 6' cable and get the following...I guess size does matter...so I'm wondering if I use 100' and an amplifier, etc as you suggest, what would the correct voltages be?

Also why the same voltage, but a difference Celcius temperature?

Zack

Sensor 0: 0.74v 24.22C 75.59F Sensor 3: 0.75v 24.71C 76.47F Sensor 0: 0.74v 23.73C 74.71F Sensor 3: 0.74v 24.22C 75.59F Sensor 0: 0.74v 23.73C 74.71F Sensor 3: 0.74v 24.22C 75.59F Sensor 0: 0.74v 23.73C 74.71F Sensor 3: 0.74v 24.22C 75.59F Sensor 0: 0.74v 23.73C 74.71F Sensor 3: 0.74v 24.22C 75.59F

A 100’ cable shows…

4.56 Volts 407.03 Celcius 764.66 Farenheight

And voltage is converted using:

//Convert voltage on the 5 volt arduino pin
int ReadDevice3 = analogRead(3);
float Voltage3 = ReadDevice3 * 5.0 / 1024;

Now I'm really confused....I turned my back to talk to somebody and the Arduino was runnng my code for a while and I noticed the following using a 100' RJ-45 cable on sensor #3.....

. . . . . Sensor 3: 4.60v 410.45C 770.81F Sensor 0: 0.74v 23.73C 74.71F Sensor 3: 4.62v 411.91C 773.45F Sensor 0: 0.74v 24.22C 75.59F Sensor 3: 4.59v 409.47C 769.05F Sensor 0: 0.74v 24.22C 75.59F Sensor 3: 4.49v 398.73C 749.71F Sensor 0: 0.74v 23.73C 74.71F Sensor 3: 4.55v 404.59C 760.26F Sensor 0: 0.74v 23.73C 74.71F Sensor 3: 4.57v 407.03C 764.66F Sensor 0: 0.74v 23.73C 74.71F Sensor 3: 4.56v 406.05C 762.90F Sensor 0: 0.74v 23.73C 74.71F Sensor 3: 4.95v 444.63C 832.33F Sensor 0: 0.74v 24.22C 75.59F Sensor 3: 0.75v 25.20C 77.35F Sensor 0: 0.74v 23.73C 74.71F Sensor 3: 0.75v 25.20C 77.35F Sensor 0: 0.74v 23.73C 74.71F Sensor 3: 0.75v 25.20C 77.35F Sensor 0: 0.74v 23.73C 74.71F Sensor 3: 0.75v 25.20C 77.35F Sensor 0: 0.74v 23.73C 74.71F Sensor 3: 0.75v 25.20C 77.35F Sensor 0: 0.74v 23.73C 74.71F Sensor 3: 0.75v 25.20C 77.35F Sensor 0: 0.74v 23.73C 74.71F Sensor 3: 0.75v 25.20C 77.35F Sensor 0: 0.74v 24.22C 75.59F Sensor 3: 0.75v 25.20C 77.35F Sensor 0: 0.74v 23.73C 74.71F . . . . .

Why would this happen?

Zack

Why would this happen

Somebody lit a match under the sensor when you weren’t looking? ;D

Good evening ZackBurns! Would it be possibile to know the hardware you are using, please? I am interested in a project for temperature monitoring in ten rooms and outside the house. Thank you! :)

I am using the Arduino Delenova (or whatever they call it) and simple analog temperature sensors the TMP36 (on my sensor is says TMP36GZ) but I don’t see that on this list…

I’m experiencing some oddities with this analog temperature sensor and not sure why. I may switch to a digital type sensor, but I don’t know if that’s as easy to query the values from.

Check out the photo posted a couple of posts back, but I’m also using an Ethernet shield and a couple of RJ-45 jacks that I just wired the sensors to. Again this may be the wrong approach. I need to do this on the cheap as I may be deploying 100+ Arduino’s and 500+ remote sensors for our company.

Zack

http://www.analog.com/en/sensors/digital-temperature-sensors/tmp36/products/product.html

Have you read the data sheet?

It suggests using a 750R series resistor at the sensor end when driving capacitive loads (which is what twisted pairs are). It could be your sensors are oscillating.

In fact the data sheet has lots of suggestions for transmitting the information over long wires. Take a look.

Thanks Mike,

I guess when in doubt - RTM. I'll look into these suggestions....and thanks for all your help!

Sorry for not reading the entire thing first!

Zack

Thank you very much!