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46  Topics / Robotics / Re: Arduino and complex robots? Possible? on: April 03, 2014, 07:03:46 pm
A microcontroller like an Arduino is your interface to the sensors/motors/etc. On a large project you should think of it as a peripheral device which should be controlled by a microprocessor-based system like a Raspberry Pi.
47  Using Arduino / Motors, Mechanics, and Power / Re: nema17 stepper window shades, 150mAh LiPo? on: April 03, 2014, 06:38:07 pm
The small gear motors that Pololu sells (and you can find elsewhere) are actually designed for window shades. With a DPDT relay and limit switches (scroll down) you can do as well or better than a stepper motor.

Your battery is designed for a small helicopter. Guess that it flies for 10 minutes at best, so it should be good for a 900ma current draw (150ma over 60 minutes =~ 900ma over 10 minutes). But I wouldn't hang LiPos around my house -- even the small risk of fire is just too much. Suggest you stick with NiMH or Lithium Ion AA cells or such.

48  Using Arduino / Project Guidance / Re: GPS, Serial LCD, and SD card... too much for the Uno's pins? on: April 03, 2014, 06:12:44 pm
I'm not familiar with the libraries being used. Isn't this saying pin 3 is being used twice?
SoftwareSerial sLCD = SoftwareSerial(3, 6);
TinyGPSPlus gps;
SoftwareSerial ss(4, 3); //pins for the GPS

It wouldn't explode since the Arduino only TX's to the LCD and RXs from the GPS. But the Arduino Cookbook would recommend you use "255" for the unneeded pin.
49  Using Arduino / Motors, Mechanics, and Power / Re: Charging circuit for a 7.4V LiPro on: April 03, 2014, 11:07:02 am
So there's no circuit board that can just disconnect the power when the battery is full? If that's true that is ridiculous.

You haven't described your project at all but it may have been a better idea to start with a charge pack designed for use with cell phones.
50  Using Arduino / General Electronics / Re: Looking for a Digital Potentiometer on: April 03, 2014, 10:52:34 am
You can put a 1K digital pot in parallel with a resistor in the 1 ohm range.
51  Using Arduino / Project Guidance / Re: Best way to track a flying object/Indoor object tracking. on: April 02, 2014, 10:56:19 pm
Then you should look at OpenCV. An IR LED on the copter will show up very brightly in the picture taken by a digital camera; OpenCV will help you do the image capture and some basic image manipulation to get the LED to stand out well in the picture. Then it's just a matter of identifying the brightest pixels in the image.

If you had a camera mounted on the copter you could point it at the ceiling where you'd have fiducial markers placed. reacTIVision will identify the x/y coordinates of the fiducial markers in the frame, and with a little trig you can get your 3D position.
52  Using Arduino / Microcontrollers / Re: Weight based system on: April 02, 2014, 05:32:10 pm
Instrumentation amps and op amps never output a full scale, 0 to VCC range. For the INA125P specifically it's a minimum of .4V to VCC - 0.9V, typical.

You have to be aware that the load cell is never going to show a perfect, 0V differential output between its signal wires; you're always going to see a little offset. If you set the gain of the InAmp too high you're going to be magnifying that offset excessively. From experience I can say that the resistance setting the gain needs to be precise to 2 ohms or less. The Instructable's suggestion of using a 10 ohm resistor is naive -- you need to fiddle with that value to see what works best for your load cell. Ideally you'd use a 50 ohm, multiturn pot for this; you would start at 50 ohms and slowly decrease the resistance right until the point you see the output start to change -- that's your ideal gain setting.

53  Using Arduino / Project Guidance / Re: Best way to track a flying object/Indoor object tracking. on: April 02, 2014, 04:35:00 pm
Using USB cameras you could use Roborealm to track a bright IR beacon (or any distinct color LED) attached on the quad. Two cameras would allow you to track it in 3D space.
54  Using Arduino / Motors, Mechanics, and Power / Re: My first 110v project - Water pump on: April 01, 2014, 11:37:02 pm
Wouldn't hurt to add extra solder to those traces on the bottom of the relay board to thicken them up.
55  Using Arduino / Project Guidance / Re: Use of load cell for monitoring specific gravity of liquid over time/arduino uno on: April 01, 2014, 11:26:16 pm
The INA125P doesn't output a full 0-5V range. See page 2 of the datasheet (Output). The maximum output "swing" given 5V operation is .4V to 4.1V, typical. Now that means that, given a perfectly manufactured load cell, you're down to a 3.7V range. Of course no load cell is perfect and will always be showing some voltage offset so that 3.7V range will be reduced even more.

Also, when you're adjusting the gain, make sure you have a 50 or 100 ohm potentiometer available. When you're off by just a couple ohms in your gain you quickly lose precision (because you'll be multiplying the aforementioned, imperfect load cell offset) so you'll need low value pots to get things set optimally.
56  Using Arduino / Project Guidance / Re: Programmed Flight Arduino Quadcopter on: March 31, 2014, 11:45:28 am
You listed a set of propellers that are inappropriate for a quadcopter. You want the "slow fly" ("SF") propellers that come in packs of four, two of which will be RH and two LH ... and then you'll want to buy three or more packs - DAMHIKT.

On a quad you need two of the props rotating in one direction and two in the other direction. If you don't have that then your copter will yaw uncontrollably.

Also suggest you consider a power distribution board for the ESCs instead of the cables. Half the weight and a lot more organized.
57  Using Arduino / Project Guidance / Re: Use of load cell for monitoring specific gravity of liquid over time/arduino uno on: March 31, 2014, 11:36:23 am
Before settling on the INA125P you should consider either the ADS1231 (Texas Instruments) or HX711 (Chinese), both 24 bit amplifiers at around the same cost as the INA125P. The problem with the INA125P, as you mentioned, is that while you get an amplified signal you're still shortchanged by the max 10 bits of precision from the Arduino (as you mentioned), and then given the imperfect load cell and such you realistically take yourself down to about 8 bits or less.
58  Using Arduino / General Electronics / Re: potting? silicone? epoxy coating? specifics on weather proofing Arduino circuit on: March 31, 2014, 09:45:55 am
I have a project running an RGB LED outside my house (lamp post) that has been running fine for two years now. It's mounted inside the post and contained in a box to keep the rain/etc. off it but still has the 1/2" holes in the top and bottom and generally open to the air (the linear LED drivers get pretty toasty). I have not seen any degradation in any of the traces, etc.

If you did want to coat it I would suggest a 2 part "laminating" epoxy if for no other reason than the fact that it's a very handy thing to have around, easy to use, and has many years of shelf life. This is the epoxy that comes in two bottles, one clear and the other yellowish clear. You can thin it down with a little alcohol (denatured alcohol) for a thinner coating. Since it's used in boat building you can be assured it's waterproof and won't crack.
59  Using Arduino / Sensors / Re: How to determine GPS accuracy? on: March 28, 2014, 01:20:33 pm
Are you saying the GPS gadget no longer calculates position above 30000 feet?

These Garmin GPSs, intended to be installed in aircraft, would certainly fit in the broad context of "commercial GPS gadgets" and are spec'ed to 55000 feet.

Those commercial units have export restrictions. If you're using a USA-made unit that doesn't report export restrictions -- that's designed for a worldwide market -- then you can be assured that it's limited to 18,000m.
60  Using Arduino / Sensors / Re: How to determine GPS accuracy? on: March 28, 2014, 11:48:52 am
high altitude balloon project
All commercial GPS gadgets are limited to 30.000 feet altitude, afaik.
The Ublox site reports 50,000m alt for their NEO line. I believe the restriction is only for US exports and the limit is 18,000m.

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