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Wifi Temperature/Humidity Help?


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#1 omnomnomsies

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Posted 07 November 2011 - 04:37 AM

I've never attempted any kind of hardware projects before. I'm quite familiar with C# programming and someone suggested I check into the Netduino products for my project. I'm attempting to create wifi enabled temperature and humidity sensors to monitor the environmental conditions of my plants and do interesting things with the data. The idea is that they will make an HTTP GET with the information on a schedule. They needn't be battery powered but if there are ultra-low powered options available that will allow me to use battery packs that would be great. After a few days of research it looks like the components below might be my best option. Can someone sanity check these for me? Is there any reason to use the NetDuino Plus if I don't need wired ethernet or the SD card? Does it somehow make the TCP stack easier to use? I also haven't seen anyone successfully use the wifi breakout I'm looking into. I need wireless N capability if possible and this is the only one that I've found? The others all say they transmit on B only. 1x Netduino 1x Wifi component from Weburban - http://store.weburba...urban/wifi.html 1x TMP-102 Temperature Sensor - http://www.sparkfun.com/products/9418 1x HIH-4030 Humidity Sensor - http://www.sparkfun.com/products/9569 If these components seem like they might work does anyone have any suggestions on what other accessories and whatnot I should pickup to make them work together? I realize that sounds a bit silly but I have exactly 0 hardware experience and I'd like to avoid $15 in shipping for a $.30 part if I can help it. On my list is: soldering iron and solder wire break apart header blocks male, female possibly an enclosure of some sort I have snips of various kinds and electrical tape already. Any help would be greatly appreciated - thanks for reading.

#2 Mario Vernari

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Posted 07 November 2011 - 08:05 AM

Hello Omno* (too hard to read for me!) and welcome to the great Netduino community.

I can't say anything about the Wifi shield, nor about Ethernet related stuffs: I'm not the right person to evaluate such a devices. Thus, I can't say whether the standard Netduino would fit you target, or you must switch to the Plus version (with Ethernet embedded).
However, bear in mind that the Plus version supports the SD memories, thus as a data logger is surely a good bet.

The probes should working fine, although you should apply some basic hardware hacking. For instance, the humidity sensor gives you an output ranging from zero to almost 5 Volts. This is too much for the Netduino analog inputs, thus you must provide a simple voltage divisor (i.e. a resistor pair).

There are some best-practice task to consider as well. For instance, I've written a small article about the noise on the analog readings. You should follow some tip to obtain a good stability on measurements.

The only bad news is the low-power capability, which is totally missing. At least, I mean an idle current below 1 mA, such having a quite long life of a normal battery.
At the moment, I'm terminating a simple circuit to both add a RTC (real-time clock) to the Netduino, and take advantage of it for placing the circuit in a sleep-then-awake mode. Perhaps may be interesting for your goal.

Finally, about the tools, I'd suggest *at least* a good/decent multimeter. Another very useful tool for anyone is working on hardware is a scope, but it's much more pricey than a simple multimeter. As long you don't perform hard tasks, a multimeter could be enough.
Hope it helps.
Cheers
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#3 Valkyrie-MT

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Posted 07 November 2011 - 09:57 PM

The probes should working fine, although you should apply some basic hardware hacking. For instance, the humidity sensor gives you an output ranging from zero to almost 5 Volts. This is too much for the Netduino analog inputs, thus you must provide a simple voltage divisor (i.e. a resistor pair).


Mario, I've noticed that the 5V is not very accurate (when using USB, could be my computer Power supply though), but the 3.3V on the Netduino is perfect. If you feed the HIH-4030 an unstable 5V, and use a voltage divider on the result, won't you get a rather unstable reading? Should you use another/independent voltage divider on the 5V to use as the Analog Reference? I've seen a post on the forum about the sensor working with 3.3V, but I think that is out of spec.

-Valkyrie-MT

#4 Magpie

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Posted 07 November 2011 - 11:05 PM

I agree with Valkyrie-MT, to get good results on your analogue conversion you need to be careful about the power going to your sensors and what you are using as your analogue reference. For simple passive sensors such a NTCs or LM335, I gave up on the internal reference and chip power rails, and now use a separate analogue power supply for both analogue reference and sensor power. It's not a complex circuit just use a separate 3 pin low dropout linear regulator, and your a2d conversion results will be much more stable.
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#5 Stefan W.

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Posted 07 November 2011 - 11:38 PM

That particular sensor asks for a 4.5V or up supply though, so you'll have no luck feeding it from a regulator that gets its input from USB ... so either add filtering or use another sensor.
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#6 phantomtypist

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Posted 07 November 2011 - 11:58 PM

Try the HIH-5030 or HIH-5031. Those are meant specifically for 3.3 volt operation.

#7 omnomnomsies

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Posted 08 November 2011 - 01:10 AM

Thanks for the information everyone. I will check into the 3.3v sensors. I had read that the 5v humidity sensor was tolerant of lower voltages and that it would scale the values down so I would just need to do conversion but another sensor seems simpler. I have been reading about Xbee products since I posted and I wonder if an overall cheaper method might be to make each sensor part of an xbee mesh network that communicates with a single netduino with a wifi and xbee connection? I picked up the book Building Wireless Sensor Networks and this seems to be the method he goes with. I suppose the difference is that I'd like to be able to avoid buying a $200 base station and I want to do my own things with the data so maybe my Netduino would act like a custom base station?

#8 monewwq1

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Posted 08 November 2011 - 01:55 AM



1x Netduino
1x Wifi component from Weburban - http://store.weburba...urban/wifi.html


Hi Omnomnomsies,

My brief review of the datasheet for the Weburban WiFi component indicates that it is designed for PIC microcontrollers, and that it requires a TCP/IP stack loaded onto the PIC. I am skeptical that this WiFi component can interface directly with Netduino, since Netduino is based on an ARM MCU core. Sure, physically it might be able to connect, but in terms of the software, I am unaware of any C# TCP/IP stack written to specifically connect Netduino with this WiFi module. I see that there are Arduino libraries for this module, so maybe it is a simple matter of porting the Arduino libraries to Netduino; however, that might not be so simple.

For Wi-Fi on Netduino, I use a Gainspan GS1011MIP module. The link there is to a forum post I made a while ago. There is sample code there to get you started. The Gainspan is the same price as the Weburban module if you get it from Sparkfun.com.



Edit: just to clarify- the Gainspan module operates at 3.3v on a UART connection, not SPI like the Weburban one, in case that matters to you.

Edit 2: I just noticed you're looking for 802.11n. The Gainspan operates on 802.11b, so this might not be a good solution for you...

Why do you need 802.11n for your project? I have found most 802.11n Wi-Fi devices are backwards compatible with 802.11b/g. I am able to run a Wi-Fi web server directly from the Gainspan and my laptop has no problem connecting. I use a Netduino Plus for the built-in SD card, to store the web pages that I serve from the module. Works great.

#9 Spork

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Posted 08 November 2011 - 02:38 AM

My two cents: I think i2c sensors might be easier for beginners to get right, compared to analog devices. Wire wrap instead of soldering. If you like what you've wrapped, you can always solder the wraps.

#10 Mario Vernari

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Posted 08 November 2011 - 05:02 AM

Sorry guys for being in late. It's totally right that the +5V supply is dirty when operating by USB, but you should consider a battery-operated device: that should be the aim. Cheers
Biggest fault of Netduino? It runs by electricity.




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