Here is a post you may find helpful: http://www.faludi.co...sensor-circuit/

Basically the way it works is that the resistance of wet soil is lower than that of dry soil. You could either make your own probe or hack one of the cheap probes from a garden supply shop.

JonnyBoats,
Thanks for the insight. So I guess reading the moisture content of something physical is slightly more of a challenge than originally thought. And that's because i can't find a sensor that will do that for me... But really isn't it the same idea as a pentiometer? One prong receiving electricity, another for it to exit, and one in the middle to read what's moving across the other two?

Very similar. It you would like to try a simple experiment you could stick two pieces of metal with wires attached into a pot of dirt. Connect one to the ground on the Netwuino and the second to one of the analog input pins. This second wire should also be connected to a resistor (try 1 MegOhm, value not critical) and the other end of the resistor to +3.3v on the Netduino. This is what is known as a pull-up resistor.

If the soil is bone dry then you should read a voltage of 3.3v (give or take) on the input pin, this is because the input pin is connected to v+ via the resistors and the resistance between the two pieces of metal is essentially infinite.

Now pour some tap water into the pot. The resistance between the two pieces of metal will now become some finite value and the voltage on the input pin will decrease.

If you were to immerse the two pieces of metal into a glass of salt water the resistance should become very low and the voltage on the input pin become close to zero.

The only real problem at this point is that the resistance also depends on the distance between the two pieces of metal in the dirt. If you wiggle the wires anc change the distance the reading will change as well. A "real" probe will be made so that the two pieces are held at a small fixed distance and usually combined into what looks like a single probe. In fact one connection is simply above the other, just like on a headphone plug that you would plug into the audio jack on your PC.

You can now buy a commercial probe if you like, and as with everything else the price will vary depending on who makes it and the required degree of accuracy.

Could you get a 1/4 inch audio jack and just stick it into the soil?

last night I was trying to work out a probe that reads the water level in my hydroponic window box. because the feed water is slightly saline, it conducts, so this approach will work great for it.

In my case, I want to read 'full' or 'empty', so I will just have two wires that are stripped at the ends, just above the low level.

I had thought about using resistance wire, with the water level forming a potentiomiter. that would allow a measure of depth.

thanks for the info!

One thing that is not clear from your question is if you are just trying to experiment or learn or if you are looking for a robust solution.

The reason I bring this up is because measuring full and empty with two wires that are stripped is cheap and easy but does not have good long term reliability. The first issue is that when a DC current passes through the probes electrolysis occurs and the wires degrade over time. One can use better probes such as platnum electrodes and use an AC rather than DC current etc.

On the other hand one can purchase for about $5 a MEMS sensor such as is used in washing machines to detect water level which outputs an analog voltage proportional to the water level. They are extremely reliable and will last practically for ever. I have used the ones from Freescale (http://www.freescale...et/MPXV4006.pdf ) for just this purpose. Take a look at the MPxx4006 family.

Currently I'm experimenting on a small scale using a window-box sized system. I'm in the process of building a greenhouse, and hope to automate it as much as possible, which is why I'm experimenting on the cheep now
For the full thing, I'll be building/buying sensors design for the long-term.

Thanks for the links! I actually have a pair or scrapped washing machines and a dishwasher, that I've been getting parts from as I need them. I'll see if I can find the sensor.

You might enjoy the video in this blog post: Plantduino Greenhouse Cares Of Your Plats While You’re Away In particular note how they use two ordinary nails to sense moisture in the ground.

All the details, parts list, schematic etc can be found at http://revoltlab.com/.

http://blogs.msdn.co...here-is-it.aspx

Microsoft is looking for hardware vendors who are interested in developing kits and modules, so you could contact them if you are interested.

Take a look at http://videos.analog...elopment-Board/

You can get one for $30 here: http://www.analog.co...ts/product.html

This board runs on 2 AA batteries and logs the data to an SD card. After your workout session you could put the SD card into your Netduino Plus and do whatever with the data.

The issue only has 2 votes on Codeplex! Go and Vote! (you might have to create an account)

http://netmf.codeplex.com/workitem/754

-Valkyrie-MT

I just made it 3.

Have you considered measuring magnetic field?

With a new release of Fritzing (0.6.2) just released, I thought it would be a good time to bump this thread. I just downloaded the new release, and (like before) it is great to have all three variants of the Netduino in there "out of the box". A big thank you to those who made it possible.

I was surprised to see that at least one supplier has started discounting Netduinos and apparently has both Netduinos and Pluses in stock.

http://www.seeedstud...etduino&x=0&y=0

Very nice tutorial, it got a tweet from me ;-)

I just got around to fooling with this and it isn't clear (to me) how to interface this to the Netduino. The video mentions interfacing the the USB but there are no details. I suppose I can look at their SDK but I believe it is C++ and would require some port to Netduino.

Has anyone actually interfaced this to a Netduino?

The easiest way to interface the TI chip to the Netduino is via the TTL level serial port, both boards have them.

Tech Junkies just posted Open Source Robot Controls which uses a Netduino Plus. It is totally open source (hardware and software). The video is excellent and includes a walk-through of the Netduino code.

Fabien Royer did a nice blog post on his Netduino-powered Game Console at http://fabienroyer.w...d-game-console/

You mean this one?

http://forums.netdui...4-game-console/

Yes, sorry. (It's still a great project though).

Sneak peek inside the lab...

When we build new products, we usually spend about 6-9 months: design, parts sourcing, testing, building test jigs, etc.

To make Gadgeteer affordable, we needed to make our own plastic sockets for Gadgeteer accessories. [These sockets are drop-in replacements for the normal, more expensive sockets. You'll also be able to make your own boards and accessories...all open source.]

We just received the first batch of sockets, so I took a photo of a handful of them.

Now we'll do temperature testing (to make sure they survive the industrial reflow oven) and hand-assemble a few prototype boards.

BTW, a big thank you to the MSR team in Cambridge for their work on Gadgeteer (past, present and future).

Chris

Disclaimer: We haven't officially announced a Gadgeteer product lineup... We do sometimes cancel projects. But I thought I'd share a sneak peek update since you have shared your enthusiasm about Gadgeteer

Chris,

I was looking at the specifications for the connectors used by the .Net Gadgeteer and I see they are rated for an average life of only 500 insertions, which seems incredibly low.

What is the MTBF for your connectors?

I ordered and received one. As a watch goes, it is extremely thick and heavy. It definitely scores major geek points though :-)

I too find this sort of project fascinating. Thanks in advance for whatever details you choose to share with us.

I have somewhat of a mixed background in that I am a radio amateur (ham radio) as well as working as a programmer all my life.

In reading this thread (and lots more like it on other forums) I believe that often times people overlook that there is a big difference between knowing enough to get something to work and thoroughly understanding it.

Consider changing the oil in your car. That is something most people can do without an understanding of how an internal combustion engine works. By the same token there are some basics that one needs to know in order to do it safely and not ruin the engine. Things like "Shut the car off before crawling underneath to drain the oil" and 'Be sure to check the oil level on the dipstick before restarting the car and then check for leaks."

Now consider a simple electric lamp. One needs to have a power source, a lamp and some wire to connect them. One does not need to understand the difference between AC and DC current, or for that matter even care.

A good electrical engineer will understand Maxwell's equations, just as someone with a degree in computer science should thoroughly understand design patterns. That having been said, I know lots of people making a living as a programmer could not implement a state machine if their life depended on it.

The plain fact is that for _most_ of the things that beginners want to do with single board computers, knowledge of graduate level engineering is simply not required. What is helpful is the level of knowledge typically required to earn a boy (or girl) scout merit badge. Much of what one needs to know is best learned in a group environment with hands on labs. One could take EE courses at a university or one could simply go to a local hackerspace and learn by doing, benefiting from the experience and knowledge of others.

For those wanting an on-line resource to gain greater exposure to basic EE, two sites I have found helpful are the EEV blog and The Signal Path. If you are rusty on the math or other academic topics (like differential equations) the Khan Academy is a great resource.

Just keep in mind that learning electrical engineering and building simple projects are not always the same.

Finally allow me to say something to the EEs here. For a programmer who already knows C# (or VB) an .Net the Netduino is an ideal first single board computer. Why? because he already has the toolchain (Visual Studio) installed and running on his computer. While there are great, open source toolchains such as GNU on Unix available for a multitude of single board computers, for a programmer who uses Visual Studio on a daily basis that would simply be one more hurtle to getting started with micro-controllers. Similarly for a person with Unix PC who regularly programs in GCC, the Netduino may not be ideal.

Mention was made of the TI MSP430 which at a cost of $4.30 delivered has to be one best deals going. Personally if I am going to make a mistake and destroy a micro-controller I would rather make the mistake with one of my TI 430s than one of my Netduino Plus at $60. Heck, many places charge more that $4.30 just to ship a Netduino! The point being that there are lots of boards and parts available and it is usually best to try many of them and learn rather than fret over finding the one best one.

I am definitely interested and would like to participate :-) Would anyone else be interested in having "box opening parties"? My thought is that a bunch of us could get together at a house, hackerspace or restaurant and all open the box together. We would all bring stuff to swap as well and then put our extra stuff into the box before sending it on to it's next destination. Not only would this save on shipping, but would be lots more fun to share the excitement with others. It would be educational as well in that instead of simply taking something out of the box and wondering "what could this be", there is a good chance that someone else would recognize it and perhaps say "oh, that's a switch from the from panel of a DEC PDP 8 just like I used to work on in college". I am in Northwest Maine, and would welcome any Netduino fan to my house anytime if you want to come by and "play" Netduino. For the box however perhaps Portland, Maine or Portsmouth, NH would be a more convenient place for a Netduino fan club get-together?

Will anyone else be at ESC Boston (Sept. 26-29) http://esc.eetimes.com/boston/?

Interested in meeting up?

I see Arduino has announced several new products ( http://arduino.cc/bl...ast-at-arduino/ ) including a new Wi-Fi shield.

I wonder if it will be Netduino compatible??

Anyway they will have them at Makerfare in NYC this weekend, so perhaps someone can check them out.

As others have pointed out, a Netduino is not the right tool when you require precise real-time programming. There are however lots of cheap micro-controllers that can measure frequency and report the results to the Netduino via I2C or many other ways.

One cheap way to do this is with a TI MSP430 board which only costs $4.30 delivered (https://estore.ti.co...-kit-P2031.aspx ) This is probably the cheapest way to do a one-off project and the TI chip has reasonably good support.

The best way to look at this is that there is no one perfect single board computer. The key is to use one appropriate to the task and remember that they are cheap enough that you can break the task down and use more than one board.

You are quite correct that the hardware is quite capable of handling this frequency measurement task with ease.

The issue is the .Net Micro Framework. If you are willing to forgo .Net and program directly to the chip in C, you can get the job done.

What s not as simple or easy is to combine the use of .Net with native code and direct control of hardware interrupts etc. It may very well be possible, and I hope you succeed as we would all like this capability. You should be prepared for some setbacks along the way.

Can an Atmel AT91SAM7X512 microcontroller support the functions of the Taos TSL235R?

I am still not convinced that I need to throw more components at this problem. Netduino has an ARM7 48MHz processor- why should we deny that there is plenty of speed right on this development board? If I were to remove the processor from the Netduino and program it directly, or remove the .Net firmware and run C/C++ on it, I am sure that this sensor would run fine. I've read in these forums that version 4.1.2 of the Netduino firmware is supposed to offer run-time native code interop. I've also read about someone's project called "Fluent", which runs code something like 20 to 30 times faster than the managed code. I've also read that you can run FreeRTOS on the Netduino platform. Can't you run a quadrocopter with FreeRTOS? Isn't that real-time?

Does version Netduino 4.1.2 have runtime native code interop? If not, when will it have this functionality? Where can I get this "Fluent" project? Where can I find resources on how to run my own C/C++ on this board?

I understand the opinion that more tools will help me solve this problem, but I would rather use what I have instead of having to then deal with connecting, learning, and powering these other pieces.

Thanks,

Nick

I just ran across this excellent, simple guide to connecting external parts to a microcontroller: http://cq.cx/interface.pl#10

It is not Netduino specific, but would work with any microcontroller.

One caution, in his examples he often shows the voltage level as 5 volts, which would be fine for an Arduino or many other microtrollers. The Netduino is a Netduino is a 3.3 volt device so just replace 5 V with 3.3V in his drawings.

He describe how to:

Light an LED from a Digital Output
Read Switch Contacts with a Digital Input
Read a Digital Signal that Goes from 0 V (LOW) to 10 V (HIGH)
Read (with Opto-Isolation) A Digital Signal
Measure a DC Voltage Between 0 V and 15 V
Measure a DC Voltage Between -15 V and 15 V
Measure a DC Voltage Between 0 V and 1.7 V
Measure the Position of a Potentiometer
Measure an Unknown Resistance
Measure a Temperature
Output Characters on an LCD
Switch a 100 mA, 10 V Load
Switch a 1 A, 10 V Load That Always Stays Connected to Ground
Switch a 10 A, 40 V Load
Switch a 120 VAC Load