25 replies to this topic

[Paolo Patierno]

Hello, I want to use the analog input pins but I don't know how it works ! I'm a newbie in electronics....some documentation on Netduino analog input ? Thanks, Paolo

[Omar (OZ)]

Hello,
I want to use the analog input pins but I don't know how it works ! I'm a newbie in electronics....some documentation on Netduino analog input ?

Thanks,
Paolo

Hello! I plan on making a tutorial on that this weekend. If you need help right away, I'll be glad to help you. What kind of analog sensor are you using? A link if you have one, would be helpful.

[Paolo Patierno]

Hello! I plan on making a tutorial on that this weekend. If you need help right away, I'll be glad to help you. What kind of analog sensor are you using? A link if you have one, would be helpful.

I'm using temperature sensor LM335Z (http://www.national....f/LM/LM335.html) but I don't know how connect it to Netduino.
Thanks,
Paolo

[Omar (OZ)]

I'm using temperature sensor LM335Z (http://www.national....f/LM/LM335.html) but I don't know how connect it to Netduino.
Thanks,
Paolo

So I looked around and it looks like you are using this: http://www.sparkfun....roducts_id=9438 . am I correct?

Also how quickly do you need this? Because I can order one and use it for my video tutorial on Friday. I myself have to mess around a little until I understand how to use it, and without one of those on me it is hard to know how to use it.

[Paolo Patierno]

So I looked around and it looks like you are using this: http://www.sparkfun....roducts_id=9438 . am I correct?

Also how quickly do you need this? Because I can order one and use it for my video tutorial on Friday. I myself have to mess around a little until I understand how to use it, and without one of those on me it is hard to know how to use it.

Yes you are correct !
But can you give me some general information on Netduino analog input...how it works, what is aref...etc etc...
Thanks,
Paolo

[bill.french]

The analog input pins basically work by returning a value between 0-1023 based on the voltage that is on the pin, relative to aref. Aref is the "analog reference" and sets the "ceiling". Typically you'd tie aref to 3.3v - which is it's maximum. Then, if you put 3.3v on the analog pin, you would get a reading of 1023. If you tied the analog input to ground, you'd get a reading of 0v. if you put 1.6v on the analog input, you'd get a reading around 512, or half the range. The analog inputs can handle a max of 3.3v.

Here's a link to some sample code:
analog sample code

In that code, there's a line:

AP0.SetRange(0, 1023);

This is the default, so it effectively doesn't do anything at all; but, if you do:

AP0.SetRange(0, 3300);

...your readings will match roughly with the actual voltage in millivolts. So, if you put 1.6v on the input, you'll get a reading around 1600 instead of 512.

Hopefully this makes sense?

[Omar (OZ)]

Hello again I suggest using this image (http://www.sparkfun....-sheet-SPAR.pdf) as a guide. If I get one of those sensors, then I'll post a tutorial.

[bill.french]

Oz: Are you sure that diagram is right? It doesn't quite make sense to me. Maybe talk me through it? Why isn't aref tied to the 3.3v line?

[Omar (OZ)]

Oz: Are you sure that diagram is right? It doesn't quite make sense to me. Maybe talk me through it? Why isn't aref tied to the 3.3v line?

I had it before, and it was quite the head scratcher... but if your sensor is getting X voltage after the 3V3 goes through a resistor... wouldn't you want the aref to recognize X voltage as the max? I may be wrong on that, but it makes sense [to me at least]

[bill.french]

I don't think it works that way, but I really don't know. Why do you have the analog input tied to the adj pin?

[Omar (OZ)]

I don't think it works that way, but I really don't know. Why do you have the analog input tied to the adj pin?

You know what... I think I'll take back my schematic... I completely messed that up. I was in a hurry to help, but that didn't do any good. Maybe I'll get one of those soon and figure it out, maybe post a tutorial.

[Paolo Patierno]

You know what... I think I'll take back my schematic... I completely messed that up. I was in a hurry to help, but that didn't do any good. Maybe I'll get one of those soon and figure it out, maybe post a tutorial.

I have connected pin + to a 2,2 K Resistor and then to +5V. The pin - to ground.
With a multimetere, I read abouta 4,88 V on pin +. This voltage isn't too big for Netduino analog input ?

Thanks,
Paolo

[bill.french]

The analog input only supports 3.3v -- but if I'm reading this right, a reading of 4.88v equates to 488K, which is 419F, which is 215C ... so unless your house is on fire, something else is wrong.

[Paolo Patierno]

The analog input only supports 3.3v -- but if I'm reading this right, a reading of 4.88v equates to 488K, which is 419F, which is 215C ... so unless your house is on fire, something else is wrong.

Where am I wrong ? I have connected wrong the pins ?
Paolo.

[bill.french]

I'm sorry, I don't know. According to this picture:



If your room is 72 degrees F, which is 295 degrees K, you should have a reading of about 2.95V, I think.

When you're measuring with the multimeter, is the netduino involved in the circuit at all? I would start with the netduino out of the picture entirely a focus on getting the right readings on a multimeter, then focus on getting them well below 3.3V to be safe for the analog inputs.

[Paolo Patierno]

I'm sorry, I don't know. According to this picture:



If your room is 72 degrees F, which is 295 degrees K, you should have a reading of about 2.95V, I think.

When you're measuring with the multimeter, is the netduino involved in the circuit at all? I would start with the netduino out of the picture entirely a focus on getting the right readings on a multimeter, then focus on getting them well below 3.3V to be safe for the analog inputs.

I use 5V Netduion board to put V+...

[bill.french]

Yeah, I don't know then -- using the 5v should be fine. Can you post a picture or a diagram or something? I wish I had one of those sensors to try it out myself.

[Paolo Patierno]

Yeah, I don't know then -- using the 5v should be fine. Can you post a picture or a diagram or something? I wish I had one of those sensors to try it out myself.

I have some difficults to post a diagram but following the connections :

LM335 - pin+ --> Resistor 2,2K --> 5 V Netduino board
|
|-------------------> Analog Input Netduino board

LM335 - pin- --> Ground Netduino board

Thanks,
Paolo

[bill.french]

ok i think I got this right -- i believe the right most pin is the - and the center pin is the +:



Is that about what you're doing, with the multimeter/analog input hooked up after the resistor?

[Paolo Patierno]

ok i think I got this right -- i believe the right most pin is the - and the center pin is the +:



Is that about what you're doing, with the multimeter/analog input hooked up after the resistor?

Yes the circuit is right...I put the multimeter on LM335 middle pin like the schema you have posted in the previous post.
Paolo.