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4966  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: arduino and underwater Rov on: April 14, 2010, 12:47:31 pm
Ethernet cable isn't designed to work under water!  At the very least I'd expect severe degradation of frequency response of long runs, and if salt water I predict a very short useful life...  Choose a marine-rated cable.

I thought the outer insulation was PVC? Of course, in a chlorinated or salt water environment it won't last, and ultimately it won't last in the long run period, but I suspect (though the OP didn't give any details) that this project won't be for commercial research use but rather for fun or an ROV contest of some sort. As long as the OP makes sure to seal up the ends well, he should be fine.

Your recommendation is spot-on though if he is planning something more robust; in that case marine-rated cable and connectors are a must (just be prepared for $$$ it will cost - jeez, some of those connectors cost more than my PC! But then again, I am not dropping my PC into the ocean).

However the symmetry of the pair means that its all common-mode interference and the signal is detected by a differential amplifier which is insensitive to common-mode signals.  cat5 definitely leaks a lot of signal out, try placing an AM radio near it!

Huh - here I thought all this time that the extra wire acted as some kind of (poor?) shield, but your explanation makes more sense. That also explains why you don't want to kink/stretch a cable as you run it (for ethernet).

As I have said before, I learn something new here every day!

4967  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: arduino and underwater Rov on: April 14, 2010, 01:17:29 am
If you use one conductor of the cat-5 connected to the antennas on either end

The reason why cat5 (and coax) consist of two conductors (or pairs) is that one conductor acts as a "shield" to prevent signals from leaking out or in. While you might be able to get away with using a single conductor for video (whether as an RF transmission or otherwise), it might bleed out and cause interference on other lines (say ones carrying data); or the signal fluctuations in those other lines could bleed into the video (making it fuzzy, or even worthless as a signal) - these fluctuation could be especially true if the lines are carrying power signals for motors and such, where the brush noise would cause snow and other stuff to bleed in. That isn't to say a shielding conductor is perfect; its only as good as its ground, and even then it may still allow leakage in both directions - but it should be much less than without using it.
4968  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: arduino and underwater Rov on: April 13, 2010, 06:51:52 pm
that junk probably could make it 70 feet on stretched out coat hangers

When I was kid, me and friend stretched about 50 feet of various cable - phone cable and speaker wire, mainly - from one side of his house to his room so he could have cable TV (we didn't have any coax). We ended up stapling and taping it up along walls, ceilings, and floors; it worked great for several months until his mom got a real installer to come out and hook him up right.

4969  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: arduino and underwater Rov on: April 13, 2010, 06:15:17 pm
that hack a day link I pointed out was doing ntsc upto around 70 feet without external amplification

Were they using impedance matching baluns, though? They sell these for security camera installations, and 70 feet seem like on the low end...?
4970  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: arduino and underwater Rov on: April 13, 2010, 01:16:58 am
If you plan to use cat5, use cat5 with stranded core wires, not solid core; the flexing otherwise over time will break the wires. Stranded core will last longer, but even it will fail given enough time. As far as video is concerned, you can get interface baluns to impedance match 75-ohm coax (with composite video) with cat5 (it will only take up another pair). Another possibility (if you have the power capability at the ROV end) is to use the Arduino as a motor/servo/sensor interface, and connect it to a small networked single-board computer (like a BeagleBoard or similar), hook the ethernet pairs up, and a web/ip cam, and use ethernet for everything; controls, sensors, camera, the whole nine yards. There's probably enough pairs left over to set up power-over-ethernet (though I am not sure what the current limits would be).

4971  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Some Basic DC Motor Questions on: April 12, 2010, 04:19:41 pm
If I could find my post I'd link it.

Here ya go!

4972  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Duemilanove for SW control? on: April 12, 2010, 12:17:47 pm
The answer to your question is "yes"; as long as within your application you can abide by the limits of the USB serial speed and such (and the limitations of the Arduino hardware, as Paul noted).

If you need a speedier interface (faster than USB serial), there are other options available there, too (Ethernet or WiFi, Bluetooth). Most applications do fine with USB serial.

You can set up the Arduino to control many things, but if you need a fully embedded solution, then develop the application using the Arduino, then set up a "standalone" version of the Arduino on your custom PCB as the "embedded" version (unless this is a "one-off" standalone application, where you're not going to need to make multiples of the device - then just embed the entire Arduino if your hardware enclosure has the space).

4973  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Coffee Level Sensor on: April 06, 2010, 12:22:47 pm
If you used a small linear CMOS sensor array on one side of the coffee pot, and a light on the other side (maybe a linear array of LEDs), you could detect the change in light levels between "no coffee" (lots of light) and "coffee" (little light, depending on the brew strength); the problem would be finding such a sensor and then interfacing to it?

How accurate does it need to be? Maybe a linear array of phototransistors or LDRs on one side, and a linear array of LEDs on the other side? Such an arrangement could give you at least "full", "half-full", and "refill" levels...

4974  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Help a Noob, win a prize (note, no prizes!) on: April 07, 2010, 11:29:27 am
Yeah - you could do it a number of ways, but the simplest would be to just send the communications down the USB serial link, then the Arduino would interpret them from there and perform whatever action you want (closing relays or activating a transistor/mosfet to simulate the "joystick" move).
4975  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: off chip data storage on: April 06, 2010, 03:31:29 pm
I ordered a cheap external EEPROM, i think for now i will settle for just storing critical coordinates, instead of the whole matrix

A particular method to keep in mind (if most of the area you are mapping is considered "empty") is the concept of "sparse arrays":

There are tons of techniques out there to "pack" what seems to be an amazing amount of data into a very small space - two of the best areas to learn about these techniques are from the game programming and demo coder worlds (especially those demos optimized for very small memory footprints; you would be floored by what can be done in 256 bytes).

Also, a review of certain "large" computer games from the 1970s and 1980s might be beneficial; many of these games (especially the larger scope turn-based and real-time strategy games) used fairly interesting techniques to pack their "worlds" (analogous to your maps) in small areas (aka, floppies) - granted, floppies have more space than you have available (most generally), but the techniques could be helpful.

4976  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Can Pololu Micro Maestro drive brushed DC motors? on: April 05, 2010, 04:18:37 pm

Your points are taken; I learn a lot here everyday - I suppose no matter how you look at it, if Pololu's Orangutan controller meets the needs, then you likely can't get much cheaper; it does seem to be everything I mentioned, minus the higher current capabilities (and I suppose even there you could potentially chain a higher current h-bridge to the one on-board, kinda like some of the homebrew "super servos" I have seen that wire a larger h-bridge to a servo's h-bridge to control a larger motor).

As far as what I was speaking of brushless motors; you would simply use an R/C ESC with reverse to run it. Since such ESCs use standard servo PWM for control, you wire it up like you would a servo, use the Servo library, and send "180" to turn one direction, and "0" for the other. I wasn't meaning to imply that you would control the brushless motor directly with the Arduino; while possible, it certainly isn't something for a beginner (and why do it at all - short of for learning sake - since there are off-the-shelf ESCs available to do it for you).

4977  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Can Pololu Micro Maestro drive brushed DC motors? on: April 05, 2010, 12:38:45 pm
thanks for the nuance

You want inexpensive, you want all-in-one, you want low space requirements, and you want Arduino compatibility (I think); sometimes the only answer to all of this is a custom-built controller, and there's nothing wrong with that.

If you think you'll only ever need to control two small DC motors (which may be the case - you don't say), then using an Orangutan controller might be best.

If, however, you want to control more DC motors, or larger DC motors, then you'll either have to custom-build your own h-bridge drivers, or purchase such driver controls - note that it might actually be cheaper, at least for larger motors, to use R/C ESCs with reverse, coupled to brushless DC motors instead (brushed DC motor controller can get expensive quickly, especially for very large motors, such as those used for wheelchairs and motorized scooters - if you want a real heart attack, check out the prices of DC motor controllers for electric vehicles!).

I have not seen such a device as a combined DC motor controller and servo controller on a single board (maybe you might find such a thing from a combat robotics supplier?); the nice thing about Pololu's offerings is that most of their products can be daisy-chained on a single serial control bus, so you can easily interface a ton of them with the Arduino (or any other microcontroller). This could make future expansion or upgrades easier in the future.

Hmm - there's another option: you could be the first to make such a "shield" for the Arduino; a board that used an ATMega328 communicating via serial (or I2C, or SPI) to the host, which could tell the module to either output a HIGH or LOW on a pin (for h-bridge control), or PWM (for servo control) - the user would then supply their servos or h-bridges as needed (bonus would also be to add analog input monitoring, so you could easily build custom "large motor" servos, using such things like windshield wiper motors and potentiometers).

Just some thoughts...

4978  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Can Pololu Micro Maestro drive brushed DC motors? on: April 05, 2010, 12:07:59 pm
Cheapest of all might be to protoboard up a custom controller yourself with a pre-bootloaded 328, and use an FTDI breakout or cable to upload, the Servo library to run your servos, and then custom build your h-bridge drivers (IC or discreet transistor/mosfet based) for your DC motors (should only require 2 pins per motor; use a shift-register if you need more outputs).

4979  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Can I control two servos simultaneously? on: April 01, 2010, 04:48:59 pm
My interest is stimulated by low-cost robot arms. I have one, but it is so low-cost it isn't servo's but just DC motors, so I will have to build all of the position encoding and feedback myself.

OWI Flex?

I've been thinking about picking one up myself for S&Gs; maybe set things up to detect limits via current monitoring. Part of me wants to hook one up to my Color Computer.

What's been stopping me (besides a ton of other projects in the queue) has been thoughts of re-creating a lightweight, low-cost version of the Armdroid arm, using foamcore or coroplast for the "body" of the arm, and adapting standard servos in some manner to allow their use at the base of the arm (so the arm doesn't have to move as much mass in the form of servos, which I think of as a step backward from the old arms of the 1980's - then again, servos are lighter and stronger, so maybe not?).

As a kid, I always wanted a robot arm for my computer; the closest I got was getting a Tomy Armatron for my birthday. Later I picked up a Popular Electronics magazine that described how to hook it up to a C=64 or Vic-20 (lots of hardware mods for that); I didn't understand anything about the electronics or hardware mods at the time, but it was a fascinating article that I kept around (and later scanned and put online - I need to put that back up on my website, now that I think about it).

By the time I had the knowledge and tools to do it, I can't bring myself to mod either of my Armatrons (I have two now; my original Tomy version, and a Radio Shack version), mainly because of fears that 10 years down the line I will find out I have "destroyed" something valuable on the collectors market (I collect Tomy robots). Even so, I may still snatch up a Radio Shack version for such crude hacking (I even have the motors used in the article; they were an item Radio Shack sold, and I bought 8 of them in two packs of four for future use).

Well, enough reminiscing...

4980  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: 24v into arduino on: April 01, 2010, 01:45:21 am
I just put 24v directly into my aruidno through pin 12 to ground (I realize I'm a idiot).

You're only an idiot if you said to yourself prior to doing it "gee, I wonder what would happen if I did this!", without researching anything...

Now, if you accidentally grabbed the wrong wire and stuck it in, or an alligator clip popped loose and shorted with another trace, or something like that, then you're not an idiot; unlucky, maybe.

Chalk it up to experience; to prevent this from happening in the future, try to build test rigs that work at the level of VCC (LEDs are your friends). Also, don't apply power or have power near your project until you have verified all connections (live power supply leads should -never- be just "lying around").

As far as your board is concerned: remove the dead bug, and inspect the socket and its solder joints carefully. Inspect the rest of the board carefully; look for burnt parts, scorch marks, bulged capacitors, etc; signs of other damage. Verify continuity between the pins on the socket and the pins on the headers. Give it a good check over. Look at the reference schematic for the board, and measure the output voltages when you apply USB vs external power (measure before and after the regulator). Verify that you have voltage from the USB port. Once you have all that done, then try plugging in another ATMega with bootloader. Power it up initially with the USB port, and verify that all looks OK. Then upload the Blink sketch, and hope everything is wonderful still...

Good luck!

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