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4981  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Is this a good deal? on: April 19, 2010, 02:38:32 pm
What exactly is the second item?

Is $66 "US dollars" or some other currency?

I concur with Paul that if that is US dollars, that's a little high (depending on shipping).
4982  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: problem in sending values serailly on: April 20, 2010, 12:11:11 pm
Why not just send the ASCII byte - 0x00, 0x01, 0x02...0x0A, 0x0B, 0x0C...0xFD, 0xFE, 0xFF?

Those values (in hex) correspond to the values 0, 1, 2...10, 11, 12...253, 254, 255. Just output those characters to the port, and read in the values on the Arduino.

For example, say you wanted the number "65" for the Arduino; ASCII value 65 equals "A" - so send an "A" (66=B, and so on).

For the lower values, you may need to get tricky, depending on the value. For example, "0" is the null character, so in C you would send "\0" (IIRC). For "10", which is the linefeed character, hex 0x0A - you would send "\r". Depending on how you wrote your serial output interface on the PC side, you may be able to get away with sending the hex values directly.

As others have noted, there are plenty of examples on this, and there are plenty of libraries that deal with this issue if that works better for you and you have the leftover memory to include one. You already know you are getting ASCII values for characters you send; just expand on this knowledge (note - it is a good idea in your loop to look for start and end characters that signify the beginning and end of the transmission; that way, spurious characters won't likely cause an unwanted action to occur).

Good luck.

 smiley
4983  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Need some advice on a Digital Potentiometer on: March 30, 2010, 04:07:52 pm
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Oooh I never thought of that.  I'll have to check if there are any nearby..

I was just asking my wife last night if we knew anybody with a non-salt water pool; I was wanting to buy some HCl myself for the same purpose, but I didn't want to store 2 gallons worth (for pools, they typically come in a box with two 1 gallon jugs). I only want about 32 oz.

You can typically find the stuff anywhere pool stuff is sold; I know our local Albertsons carries it; Frys (groceries) carries it; Safeway has it too. You might also be able to find it in higher concentrations at a janitorial supply or hardware store as a concrete cleaner/etchant...

 smiley
4984  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Need some advice on a Digital Potentiometer on: March 30, 2010, 12:22:00 pm
TchnclFl:

First off, I think you are selling yourself short; I really think you have the skills to pull this off, and you can read that tech sheet and such - just take your time, and don't get in a rush.

From what I can see on that sheet, it doesn't look too difficult to interface with. I would also bet that the code from the original example could be adapted (just serial comms in probably a slightly different format; I didn't look too closely at it, but it seemed workable).

I think if you take the time to compare things, you can get this to work out. From what I could see, there really didn't seem much to it (famous last words, I know).

 smiley-wink

The only other thing that concerns me, though, and once again, I didn't look hard into it, is whether the digital pot you are using will have the range needed (or if you can adjust it using a fixed resistor either in parallel or serial with the digital pot) for the LM317, as well as the current handling capability. If you can verify that, then it is simply a matter of hooking up the SPI interface and writing code to control it.

I would certain try to modify or add on to the original library, to expand it for others. If I were taking it on, actually, I would probably want to try to make the library more modular, to allow for the easy addition of future chipsets (at least in the same family). But that is just me. I certainly think you could get this to work with this digital pot.

I also noted that the chip you picked has multiple pots (2); you could use the other for variable current control in the future (not sure how that actually works, though - I've got little experience with power supply design).

If you can make this thing be a variable voltage controlled power supply, from something like 0-15VDC at 2-10 A output - I would love something like that for my bench for cheap (I've been pricing benchtop supplies, and such supplies are anything but inexpensive - not out of my price range, but I would love to find something cheaper).

 smiley
4985  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Where to get larger pushbuttons? on: April 21, 2010, 11:24:42 am
Not sure if they'll have the size you need; but arcade machine controls come to mind:

http://www.happ.com/pushbuttons/pushbuttons.htm
http://www.happ.com/pushbuttons/5700043x.htm

They don't come cheap, though!

 smiley
4986  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: working with multipel serial devices? on: April 19, 2010, 12:27:48 pm
To give you a possible answer, though - have you thought about RS-485?
4987  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: working with multipel serial devices? on: April 19, 2010, 12:26:25 pm
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How would you connect 17(yes thats right seventeen) serial devices(sensors) and get data from them to a computer? 17 USB ports seems too much to expect.

You must be young (that, or forgetful, or senile, or maybe you are like a lot of us and just block those memories - how I wish I could forget; the JD does nothing)...

A long time ago, 17 serial dumb-terminals (and line printers) spread over an office building was a small installation...

 smiley

/I feel old...
4988  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Building a rover on: April 19, 2010, 03:05:00 pm
The biggest problem with a PowerWheels (well, other than needing high-amperage motor drivers, and a custom high-torque servo for steering), is storage - that thing takes up so much room in my shop (which isn't as big as I would wish to have - something the size of Costco would be a nice size).

 ;D
4989  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Building a rover on: April 19, 2010, 11:33:45 am
A question I have: do you have the rover part of your rover, or do you have an idea of what you will use?

Scale is important here; the bigger the rover, the more you can put on it (to a point). For instance, I am building a "rover" - it is being based on a PowerWheels H2. So far, I know it can haul my fat butt around (200+ lbs), so my choices of what to control it with are nearly unlimited.

Which is why I am using an Intel ATOM motherboard with a PicoPSU running off on-board SLA batteries. I am using an Arduino merely for steering and drive motor control (as well as pass-thru for servo commands to a Pololu MSSC).

If you are planning something smaller, keep in mind power requirements of everything you are planning to use - sometimes, it might be easier to plan everything, build all the component building blocks, find out the power requirements from those experiments, then choose your chassis size based on that.

Depending on your needs and desires, you might find you need more processing power than you have battery to run it; I initially had a plan to use a smaller 2WD truck platform (a cheap New Bright toy truck) that was fairly big, but didn't have the power to allow me to put a full PC on-board (nowadays, though, I could possibly choose a BeagleBoard or similar micro PC mobo) - so I planned on using an RF interface of some sort, do all my coding and testing in that manner, then migrate everything together into the next step which was to be the larger PowerWheels base.

What ended up happening though is I found a colleague who had a spending problem; he went ahead (against my advice) and bought the PowerWheels - after he left the project, I bought everything back (he ended up liking the Arduino, and last I heard he was performing some gardening/growing experiments with it). So, we (and now I) have decided to stick with that larger platform and skip the initial one.

You could do something similar, though - off-load processing power to an external computer connected by xbee, RF, or some other wireless system (unless you are building it for a contest that disallows this). If you need vision processing, use a wireless camera and feed it into the "base" computer with a capture device and process it that way. Other sensors and such can send readings back via the wireless interface. This would allow you to have more processing power available than you have power (or space) on-board; in the future if you move to a larger platform, it can be easy to migrate.

Good luck with your rover!

 smiley
4990  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Which pin controls the motors? on: April 18, 2010, 02:55:23 pm
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Yeah, works great for double-sided and multi-layer boards!


For double sided boards, you can set up layers and invert/flip the bottom/top (whichever one you consider "the other side"), and alter the alpha channel for a particular color to allow "see thru"; stack them as layers in your editor, and alter the transparency to allow you to see the traces as you track them.

Obviously this won't work for multi-layer boards, but even in that circumstance using this method may reveal clues that can help you find nearby pins and such.

I know all of this from experience; many moons ago I was involved in the "hacking" of a set top box called the Acer NT-150, which inside was essentially a AMD 586/133 motherboard with extra components for TV signal mixing (among other things; it also had a built in smart card reader). People wanted to add a mouse, which it lacked; one of the members of the group showed me the solution he used for tracing pads from the Super I/O chipset to empty pads of what looked like a MAX232 chip on the motherboard - he and several others used this method over a period of about a week to reverse engineer the chip, which was then sourced, soldered in place, and gave the board back a DB9 serial port for a mouse.

So I know the method is more than valid for this purpose, even on a multi-layer board like a PC motherboard.

 smiley
4991  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Which pin controls the motors? on: April 18, 2010, 02:26:39 am
To trace this easily, take the board, lay it flat on a scanner square with the edges, and scan it, both the front and the back. Play with the resolution; the smaller the traces, the higher the scan resolution you should use. Then use a tool like PhotoShop or the Gimp to flood fill the traces (filling "similar" colors) from part to part, via to via, in a contrasting color (yellow or red work well). This is a real handy way to trace and reverse engineer a board, even when it has small, close-together traces for SMT work; just increase the resolution of the scan to make everything larger so the flood fill can work properly. Its not a perfect method, but when used in conjunction with standard tracing methods (namely looking at it until your eyes bleed), it can be a great help.

 smiley
4992  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Where to start? on: April 16, 2010, 06:21:18 pm
The easiest "main piece" to get is the bog-standard Arduino Duemilanove, like this one:

http://www.sparkfun.com/commerce/product_info.php?products_id=666

Gotta love the PID (product ID)!

Anyhow, this is really the "basic board" that you can start with (comes with the 328 - you don't see many boards out there anymore with the 168 or smiley-cool.

Most shields and such are designed to work with this board; as your skills progress, you can look into offerings in smaller packages (like the Pro or Nano, or even the LilyPad).

If you like a lower profile (and don't mind having a non-removable version of the ATMega on-board), check out this one - it uses a mini USB connector, and all smt parts to keep things low to the ground, so to speak (the small USB connector is kinda nice; some shields have components placed over/near the standard USB port on the Arduino, and you have to put a bit a tape over it to keep it from shorting):

http://www.seeedstudio.com/depot/seeeduino-v328-fully-assembledatmega-328-p-439.html?cPath=27

It also has other features that can be handy to users.

There are plenty of other variants available that incorporate different things on-board instead of on a shield (on-board wi-fi and ethernet are becoming a popular thing), but the standard Arduino is still what I think most people use and develop with.

 smiley
4993  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Need ATmegas TQFP Package on: April 16, 2010, 05:14:23 pm
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other than China-shipping takes too long

You are probably SOL then, unless you can find a kind soul who has some available (and isn't hoarding them because of the same issue).

Have you tried contacting any of the asian suppliers (by phone) and purchasing what you need (a tray's worth would probably be the minimum if you get very lucky) and having them FedEx'd overnighted? Have you contacted Atmel directly (again, by phone) and asked for the same thing (although they probably want a huge order; but maybe you could get friendly and they could help you work something out with one of their manufacturers in China to do the FedEx thing)?

Unfortunately it seems like a lot of stuff right now in the uC marketplace (and peripheral stuff) is only available from China; I am not sure exactly why, though...

Good luck!

 smiley

[edit]Researching on another topic, I think the reason why there are so few available on the market has to do more with the fact that Atmel has only a single fab line right now (in Colorado Springs), and what stock was available was (mostly?) bought up by suppliers in China...? Not sure...[/edit]
4994  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Projections? on: April 16, 2010, 12:16:51 pm
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As a neat 'addon' for this i thought of some sort of HUD for the frontal glass

If this is for car usage, you probably can't put a piece of frosted glass or film on your front window (might violate some vehicular window tinting or such law - check your local laws). Does it need to be for day and night, or night-time usage only? If night-time only, then you might be able to get away with reflection off the glass (though you will need to come up with some other method to undistort the image).

 smiley
4995  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Projections? on: April 15, 2010, 12:29:35 pm
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Also - is it possible to 'beam' such projections onto glass?

If the glass is frosted or ground (for back projection) it would. But it would need to be a fairly bright image. As Osgeld noted, I doubt that the LCD "opaque" state is as opaque as needed for such projection (this is the "black" contrast issue you see on LCD TVs, for instance). Also, I doubt you will be able to dissect a GLCD to the point of adding your own backlight.

I am not absolutely certain, but I think the way those alarm clocks work is by using bright 7-segment (or 5x7) LED displays, and then a simple magnifying lens arrangement for the projection - rather than LCDs.

 smiley
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