@cr0sh
There are formulas how the speed of sound depends on temperature and humidity,

Well - that's definitely very interesting, but I am not sure whether it could work in the application I am thinking of (the paper seemed to indicate long distance measuring, but I didn't read it in detail).

First - realize that this project of mine is no where close to being implemented or worked on, yet - it's all blue sky right now. Basically, I have an old Friendly Robotics mower that I eventually want to get working again. I plan on replacing the border sensing wire system with a hall-effect switch system and permanent magnets placed around perimeter areas (at least, I think this will work). I will probably also replace the entire on-board controller with something custom (and likely Arduino-based, but it may use something else).

What I want to implement, though, is something more intelligent than a random "bump-n-mow" system - something that knows where there is grass to be mowed, and where there isn't (either because there isn't any grass, or because the grass has already been mowed there). I've thought of numerous possible means, some simple, some more complex, some robust, some less so - one or more methods might be necessary to implement. One of the methods I've thought about was to measure the humidity level.

Basically - the idea (which I haven't experimented with yet) is that freshly mowed grass could be distinguished from un-mowed grass by humidity level. It may or may not be a workable idea; it may need to be something used in combination with other methods to make that determination. Ultimately, the mower robot could know when and where there is unmowed grass, and turn on/off the blade motors as needed as it mows, rather than running them continuously (and thus, it should have a longer run-time).

Just thoughts right now, like I said - but I am saving that information you provided in case it might help when I get to it...thanks!

Yet I still can't find a high-speed humidity detector (plenty of low speed ones, but I need one that can detect distinct changes in atmospheric moisture level in less than a second)...

Weep for humanity:

http://www.reddit.com/r/talesfromtechsupport
http://www.reddit.com/r/Justrolledintotheshop/

Here's how:

http://en.wikipedia.org/wiki/Flexible_electronics

So its a small current ryt? now can i use  L298N ?
breakout board is good but i wanna make this. Ill gain more knowledge ryt..
can i use a  12V 2AH battery pack for the 5V motor?

You can, but for your needs and current and such, the voltage drop (and the heat output) of the L298 is going to be horrendous; at 1 Amp, according to the datasheet (and alluded to by Erdin above ya!) - total drop is close to 5 volts. So - if you used a 12V pack, that would leave 7 volts to the motor, which is too high for a 5 volt motor. Now - if you went with a 9.6 volt pack, that would be much better - leaving you with close to 5 volts for the motor needed (and dumping less voltage through the h-bridge, as heat).

As far as actually "making" such a board - you need to realize that the L298 does not have a standard 0.1 inch pin-spacing pinout. Basically, both sets of pins -are- 0.1 inch between pins, but one row of pins is shifted by 0.05 inch. This makes it nearly impossible to use on a breadboard or standard perfboard.

You can try to bend the pins to fit - it's possible to do - but it's also very easy to break the pins off the IC as well. A better alternative is to get one of these:

http://www.jrhackett.net/L298adapter.shtml

...or - if you still want to assemble it, but gather the parts yourself - he also sells this:

http://www.jrhackett.net/L298brdInfo.shtml

Final note: You -will- need a real heatsink bolted (with heatsink grease/paste) to the L298. The problem is, of course, finding one. I have yet to find where to get the aluminum extrusion profiles (let alone just the heatsinks) the chinese companies use for the L298 Multiwatt15 devices. But you can't skip using one; it is needed, otherwise the chip will go into thermal shutdown when it overheats. So think about what you will use, if you go this route.

Personally, with all of these drawbacks, I would look for a different solution (preferably MOSFET based).

Good luck!

I vow to not use any cloud based software. Anything I have tried so far has been too sllow.

Speed would be the least of my worries - did you hear what happened to Tinkercad? Probably the easiest to use online 3D CAD program around, designed to allow you to quickly create models, etc - store them online or download the an STL file to send to your 3D printer (or upload to several 3D printing services if you wanted). I had heard about them some time ago, then about a week or so ago I decided to give them a longer "try" - and inside of a couple of hours, I had designed a simple bracket meant to hold a laser module (like something you'd mount on a robot or such). It was accurate down to a fraction of a millimeter; I was seriously tempted to have the STL file printed. I realized that this was the software I had been looking for to jump into 3D printing - CAD software is anything but easy, but they had made it easy - extremely easy, and affordable, too.

Then a couple of days later, they sent out a press release stating they were discontinuing the software to focus on a different market segment which would be based around the distributed 3D engine they had created for processing the Tinkercad modeling - and this new system would be for the simulation market. Tinkercad is no more.

...and there isn't a comparable piece of software to replace it, either. I started playing around with other options - the best I have found - so far - has been FreeCAD - but even it is no where near as simple and easy to use as Tinkercad. Shapesmith is a nice online and similar piece of software (and open source and free), but it still has a long ways to go before it can be like Tinkercad. Other offerings either won't work for me (Sketchup is Windows only - and barely works in Wine - and isn't simple to work with, either) - or are way, way too complex (Blender, for instance). I've thought about things like OpenSCAD (and OpenJSCAD, etc) - I like the nature of "program your parts" - but at the same time, it seems a bit abstract.

Tinkercad had built up a great community, got a lot of great testing, then tried to switch to a pay model that people apparently balked at (personally, I thought $20.00 a month was an absurd bargain for what you got); now that community has nothing to replace it, and likely won't support anybody wanting donations to fund a development effort, either (since they wouldn't pay for access for the low-cost Tinkercad offering)...

I can't blame Tinkercad for doing what they did - they need to make money to survive as a business, and apparently, there isn't money to be made from 3D printer enthusiasts for easy-to-use 3D CAD software (which I don't get - it's the software that's the toughest part of 3D printing - at least, if you want to do anything custom). Even so - they pulled the rug out from under a lot of people - and now those people have few options to select - currently - on where to go for similar software.

Cloud software support that can just go "poof!" one day reminds me of proprietary closed-source software, that can easily do the same thing (or the company go under) - I guess that's why I am now throwing my lot in with open solutions at least as far as CAD goes - as well as circuit design. Hopefully more people wise up and get tired of being "burned" by proprietary and closed source offerings.

Something makes me doubt it, though...

If I want to buy some gear motors that have high torque and high speed to move a heavy (about 10-20 pounds) robot at about 5MPH, what gear motor specs should I look for?

The long answer? See my post here:

http://arduino.cc/forum/index.php/topic,158924.0.html

Download and unzip the book - read section 5 (Power Transmission Elements 1) - mainly parts 13-16, section 6 (Power Transmission Elements 2), and section 7 (Power Systems) - mainly parts 13-20.

That is, if you want to do it -right- and have a real answer - yes, doing things right isn't easy, that's why courses like these on mechanical engineering exist at major universities like MIT. Be glad that they give out such an awesome book for free, though!



One of the biggest problems with your description that you don't mention, though, is how large your wheels are going to be? That will have a bearing on everything; you need to understand how torque works (it's measured in a variety of ways - generally ounce-inch/inch-ounces, pound-inches/inch-pounds, pound-feet/foot-pounds, gram-centimeters, kg-centimeters, etc).

For example, if a motor is rated with a torque of 20 inch-pounds, what that means is that the motor could lift (up-down) a weight of 20 pounds with a lever attached to the shaft that was one inch long - measured from the center of the shaft. Conversely, it also means that if the lever was 20 inches long, it could only lift 1 pound. If the lever was 10 inches long, it could move 10 pounds. See how that works?

Now - a wheel is nothing more than an infinite lever (ie, sweep the lever in a circle - notice how it forms a circular wheel shape). Now, on a level surface, it's not going to take as much torque to move that wheel with the load attached - in a horizontal fashion, as it would in a vertical fashion (which approximates the scenario above with the lever example). That book I referenced above details how it really works, taking into account the forces in both the horizontal axis of travel (which is mainly friction and rest-mass of the robot), and the vertical force of gravity. Some trig comes into play there as well (although you are only working with 90 degrees, but it becomes more important once slopes are involved). What I am trying to get at here, is that there are means to calculate what you want to do.

Now - maybe you don't know, or don't want to calculate it - so what can you do? Well, you can always use the "worst case" scenario I mentioned above - pretend the wheels of the robot need to lift the robot straight up. If you have 6 inch wheels, that's a 3 inch lever (approximately). You want to move 20 lbs (straight up), so a 60 inch-pound (or 320 oz-inch) torque specification for the motor should do the trick (20 x 3 = 60). That will likely be overkill (because your robot won't be moving straight up, obviously - unless you are making a wall climber or something!), and it doesn't take into account a ton of other factors, but it will get you in the ballpark.

Note that you will likely not want to attach the wheels directly to the motor, as the motor's bearing likely can't take the strain in the long run, but that is just my suggestion from an engineering perspective; you are free to do what you want (which includes spend more money when a motor burns out).

One more thing: The above approximation assumes you are only using one motor to move the robot; if you were to use two or more motors, of course you would want to divide and such.

Finally - another crude way to approach the problem is to build your robot frame, and attach the wheels you are going to use in their approximate locations (sans motors), and load up the frame with the amount of weight you intend to move. Then attach a fish scale to one end, and pull it along the ground, noting how many pounds or whatever it took to move it. Let's say it took 10 pounds of pull to move the frame loaded with 20 pounds of weight. You are still using the 6 inch wheels.

So - 10 pounds with a 3 inch lever is 30 inch-pounds of torque needed. Granted, this would only account for level surfaces; you might want to also pull your contraption up a 45 degree slope, and use that measurement of pulling weight to redo your calcs, to give you a better margin...

ok. in the first picture, the audio xformer (in the circle marked 'A') i have the device. it's a radioshack #273-1380 audio xformer. it has four wires.. i can figure out the names for them via a datasheet, no problem. but that symbol in the schematic looks weird, how do i hook it up?

Look at the picture on the Radio Shack website:

http://www.radioshack.com/product/index.jsp?productId=2103254

See how on the transformer the blue and green wire exits from one side, and the red and white wire exits from the other (far) side in the picture? Those correspond to each of the two "sides" on the schematic. The rounded bumpy lines on the symbol represent the coil on each side of the transformer; notice the lack of anything between the coils on the schematic - this generally means it's an air-gap core, or at least a non-ferrous core (if it were to have an ferrous core, there would be double lines between the coil lines on the symbol). I notice that there's no numbers or ratio shown on the symbol, so likely this is just a matching transformer, so either pair of wires may be connected for either side; however, you must wire the same opposite pair of wires on the "+" side to ensure polarity of the signals being passed (ie - the top wires on either side could be green and white, while the bottom could be blue and red). I hope that makes sense.

next, is B. it looks like a simple power circuit.. but why do i need to wire it to ground between the batteries.. and isn't the batteries already ground and voltage? so.. i would just be wiring that one battery to itself.. which is dangerous.

No - what you are looking at there is called a double-ended power supply: You connect the two batteries in series (in this case, a pair of 9 volt PP3 batteries), then tap the center of the series connection for your ground reference. Then - the negative pole of one of the batteries become -9 volts DC, and the positive pole of the other battery is +9 volts DC. The reason you need this for this circuit, is because the dual op-amp IC used (#276-1715) requires a dual-ended power supply; ie, one capable of providing both positive and negative voltage levels. The rest of the circuit - wherever a ground symbol is shown - MUST be connected to the ground reference of that center tap.

C. U1a and U1b are IC chips. i don't know what that symbol means though. does the plus and minus refer to certain pins? the only thing i'm certain is that the tip of the triangle must correspond to the 'output' pin. if you need a datasheet, the IC is a 'dual op amp' radioshack # 276-1715

Yes - see this datasheet - page 3 (TL082 - top middle pinout diagram):

http://www.ti.com/lit/ds/symlink/tl082.pdf

VCC+ ( pin 8 ) goes to the positive voltage supply output, VCC- ( pin 4 ) to the negative voltage supply output. For one of the op-amps in the schematic, 1IN+ ( pin 3 ), 1IN- ( pin 2 ), and 1OUT ( pin 1 ) are connected, and for the other op-amp, 2IN+ ( pin 5 ), 2IN- ( pin 6 ), and 2OUT ( pin 7 ) are connected; the "+" and "-" symbols on the op-amp schematic symbols indicate which you connect; there are two op-amps in the IC corresponding to the two op-amp symbols on the schematic. The +V and -V symbols near the op-amp symbols on the schematic indicate to hook up to the dual-ended supply in your diagram marked "B".

D. again, this is an xformer.. radioshack #273-1380 although this time, it looks like this xformer only has two wires. the other one had 4. mind you, i haven't bought this yet.. the only picture i have is on the radioshack website there.

I'm not sure where you get that it only has two wires; the picture I am looking at, the same one I indicated earlier and linked two - has 4 wires; the transformers are identical - they are just used as impedance matching transformers for audio signal transfer purposes. Is there something I am missing?

and where the big X is, i'm using an arduino circuit instead of that very costly precision waveform generator chip.

the second picture is just so if you can't see clearly under my writing in the first.

onto the third picture

i have two questions here...

1. the part of the circuit labled 'AMP' it looks like a potenimeter? but both amp chips i have are chips. so, what does that mean?

I can't see your third picture clearly - it is too small, and blurry, so I don't know what you are meaning...?

2. while i know what a normal capasitor looks like, i don't know what i'm supposed to do here. instead of just the two lines going paralell, one is a semicircle.. and the other is straight.. then there is a + sign above it. what does that mean? is there a difference between the normal capasitor symbol and this one?

This is easy to answer, simply because it is a common part: What you are looking at is the symbol for a polarized electrolytic capacitor. These capacitors typically look like small "cans" (see the second picture here):

http://en.wikipedia.org/wiki/Electrolytic_capacitor

Note the "-" symbol on the capacitor body in the picture; notice how it is near one of the leads. That lead is the "negative" lead, and the other lead is the "positive" lead, and it must be oriented properly to the schematic in order for it to work (the "+" symbol on the schematic is likely near one or the other lines leading away from the capacitor - unfortunately, I can't see it due to the reasons stated above). If you don't orient it properly, bad things can happen, depending on what it is being used for (for signal filtering, maybe not much; when used for power filtering, you can get a small explosion, fire, smoke, etc!).

The other symbol for a capacitor you are referring to - with parallel lines - refers to a non-polarized capacitor; which may be oriented in either direction without any problems. A common type is the so-called ceramic capacitor family (there are many others):

http://en.wikipedia.org/wiki/Ceramic_capacitor

Hope that helps...

I think I would try to get a single sensor working, with a single arduino and display - then try mounting the sensor at the various corners, and see what happens. The main concern here would be whether you can communicate with the sensor over your wiring to the sensor back to the arduino in such an environment; automobiles aren't very forgiving to electronics, and slapping something together and sticking it to your car may or may not work the first time out (or one or more sensors may work, but the others don't, plus noise issues from the car's electrical system, voltage spikes and sags, etc - ugly).

I think if I were doing this, I would set up each sensor with a standalone arduino (a simple ATTiny84 or 85 would be fine, I think), then communicate back to a "master arduino" via some kind of serial interface and protocol (RS-485, CANBUS or something similar would be ideal). Of course, that would necessitate more parts, more programming, more complexity, providing power for each sub-module, etc; but at least the likelyhood of the measurements coming through properly would be increased.

Just something to think about - it may be that a simple solution will work just fine; with proper routing of the wiring, and perhaps using some kind of shielded cabling between the arduino and sensors, along with either some very good filtering of the power to the Arduino (or a separate battery) - there won't be any problems. I'd just do some experimentation first...

Thank you! And yeah I didn't mean solder everything including the arduino lol But okay for sure, then I'll solder. And So would you say it's better if I just solder all 4? So that if in the future I decide to stack it'll be possible?

Not only if you decide to stack, but if the shield you're stacking on needs a pin that is on a header you didn't solder - well, that would be a problem, see?

As far as soldering the headers: If these are so-called "long pin stackable headers" - to do a good job of alignment will take a bit of effort. The best way is to put them through the holes on the shield, then stack another shield on top, and flip the whole assembly over. Make sure the shield to be soldered is flush and even with all of the header plastic, then solder the two end-pins of each header (they can just be a quick tack solder joint if you want), then pull off the shield you used for alignment. Place the shield you are soldering upside down on a flat surface, and finish all solder joints.

Read the specs - "excellent resistance to: abrasion, moisture,  alkalies, acid, copper
corrosion and varying weather conditions. It is a polyvinyl  chloride (PVC) tape that is
flame-retardant and conformable. 3M Temflex 1700 Tape provides excellent mechanical
protection with minimum bulk. It is a UL Listed and CSA Certified “Insulating Tape.
...  rated up to 600 volts".

I love 3M electrical tape - it's so much better than the generic stuff; very pliable, even in the cold. You may spend a little more on it per roll, but it's worth it!

Kapton tape is used a lot in industry.
That's adhesive, and it's tape.

...and it's expensive - but still useful to have a roll for when you really, really need it (mainly for it's resistance to heat); btw - did you ever see the amount of kapton tape that NASA put on the Curiosity rover? There must've been a few hundred dollars worth of that tape on that machine (granted, that's a pittance compared to the cost of everything else)...

Hey all - I recently found this interesting instructable via Reddit:

http://www.instructables.com/id/How-to-Build-your-Everything-Really-Really-Fast/?ALLSTEPS

It covers a ton of interesting material regarding mechanical design and such, which may be of interest to anyone building (or thinking of building) a robot or other machinery. At the end, it mentioned a book called "FUNdaMENTALs of Design" by Alexander H. Slocum of MIT. The link given at the end was broken, but with some googling, I managed to find the book - which is a set of free PDFs:

http://pergatory.mit.edu/2.007/resources/FUNdaMENTALS.html

It also comes with a variety of Excel design spreadsheets, which are referenced in the book. Be warned, this book does not seem like it is for beginners at all, but it does seem very interesting, and it's layout format (if it were printed) is also rather unique (right-hand pages are quick-ref pictorials mostly, and left-hand pages are the in-depth details for the pictorials).

Hope someone finds it interesting like I did...

First off, I am glad that there will likely be an SO forum for the Arduino - but to somehow say it could or should replace this community is daft in the extreme.

Myself and other long-time members of this community that has grown up here around arduino.cc have gone through and helped each other in immense ways over the years. We even survived the transition to this "new forum" from the old one (and part of me still misses that old one!). You can't just barge in here and demand a bunch of changes; that ain't gunna fly (whoops! sorry, slipped into redneck mode there - heh!)...

The documentation that is here on this site is for the base Arduino only, for the most part; anything extra like ethernet and such is up to the providers of those shields and modules. If you don't like it - do something about it. We aren't here for your beck-and-call; if you want better documentation, set up a blog and write better documentation, then post it here for us to see. You'll provide a valuable service to the community, and gain credit that way. Heck, you could even just post a thread about the better documentation, or post it in the playground, or whatever. Just don't expect to scream and whine about something and get it fixed - participation is key, here.

Now - I agree that search can be a pain - which is why I tend to use google search to search the site (heck, google has most of it indexed anyhow). As far as all the features and such you don't like - some of use them and like them very much, thank you - we like options. Some of us also don't mind a ton of information and "clutter" (you should see some of our workshops that we assemble electronics in - you'd probably have a heart attack).

Also - as far as the number of forums - I actually think (IIRC?) that the number of forums is way better than what we had in the past - in the past, we had too few forums, and so things were jumbled all up everywhere - you had so much intermixing of projects, questions, and such going in the wrong forums and wherever, that it was really hard to follow. You really want to return to that? Hah - you don't even know - you weren't here, then...

I start a swarm robotic project, and there's something I don't understand.
If each robot is equiped with a sonar (SR04 for example), how may "robot A" ignore the square wave emitted by "robot B" ?

Well - it may not be able to. That's one of the challenges - how to deal with the cross-talk. One way to do it would be to set up on each robot some kind of receiver, then on each robot, when it pings, it transmits a signal to all the other receivers (and doesn't listen to its own receiver of course!). Basically yelling to all the other robots "hey, I'm talking here - everybody else shut up!" - so the other robots know not to ping for a bit (nor listen for a ping).

If line-of-sight can be guaranteed, that signal could be a simple IR LED and the receiver an IR remote control receiver module (with appropriate optics added to both to allow for 360 degree coverage and reception). Alternatively, if line-of-sight isn't possible - then using small radio transmitter and receiver to communicate.