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1  Using Arduino / Sensors / Re: Which IMU, any at all? on: November 21, 2012, 01:01:25 am
so what does an IMU put out, data wise?

I'm only going to poll the data sensors every 10 seconds or so, and simply putting the data onto a display screen on the controller. I just want to be able to know where it is incase I have a mechanical failure, or if it's about to go turtle from rough terrain. The rover's top speed is 3 MPH and I'll be downthrottled if It needs to crawl rough terrain. Powered by 1800W of electric motors and using six ATV tires, it won't be getting stuck unless it breaks the driveline. But that's where I might want to know if it's trying to go turtle, say, if it's climbing a slope that's 40 degrees inclined [pitch] and 30 degrees slanted [roll].
2  Using Arduino / Sensors / Re: Which IMU, any at all? on: November 20, 2012, 09:37:09 pm
so how exactly does the IMU provide positional data? I'm trying to wrap my mind around this concept...
3  Using Arduino / Sensors / Re: Which IMU, any at all? on: November 20, 2012, 01:54:59 pm
I'm trying to figure out how all 3 components in 9DOF work together, based on this post: https://forum.sparkfun.com/viewtopic.php?f=14&t=24226

accelerometer + trigonometery = where 'down' is

magnetometer = where magnetic north is (what do the other 2 axis do??)

gyro = measures how quickly it is moving pitch/yaw/roll (which I really don't really need to know, I don't think? I want it's position, not how fast it's getting there)
4  Using Arduino / Sensors / Which IMU, any at all? on: November 20, 2012, 01:22:51 am
Ground rover with long wireless range (1/4 mile or more depending on obstacles), will have GPS on it for absolute location.

Which IMU would work best and is easiest to process the output of?

9DOF Razor -> https://www.sparkfun.com/products/10736

ArduIMU V3 -> https://www.sparkfun.com/products/11055

I'm looking for the following outputs at the minimum:

pitch
yaw/heading
roll

Basically, from 1/4 mile away, with no camera imagery, I want to be able to know the exact position of the rover- The GPS lat/long are a given, but I want to know if it's halfway onto it's side climbing a steep angled slope, what direction it's pointing, and things like that.

With that said, do I really need a full IMU, or would I be wasting my money, better off to get a 3 axis Gyro or accelerometer?
5  Using Arduino / Project Guidance / two mcu's reading off single hall sensor on: October 23, 2012, 02:27:21 am
hall sensor is for detecting RPM, has Vcc, gnd, and return. Not sure about the specifics, but it goes to an OEM data logger.

I'd like to tap the output into an arduino for alternative purposes. I have reason to believe that the OEM DL runs at 5 volts already, but I don't know that for a fact.

My main question, will adding another detection circuit to the hall's output effect anything?
6  Using Arduino / Project Guidance / Re: Mega 2560 servo pins & Fio AREF on: September 01, 2012, 02:18:18 am
Hi
Servos can go on any pin if you are using the servo library, or try this trick to put all of them on one pin -

http://rcarduino.blogspot.com/2012/08/arduino-serial-servos.html

Duane B

rcarduino.blogspot.com

Well it says 48 servos...the mega has 53 digital and 16 analog..which pins go to which timers?

Going to have only 2 or 4 servos themselves. The other 13-15 will be motors running on ESC's....and not just little ones. The robot will be running on 2 optima yellow tops if that says anything. If there's room, might fit 4 of the buggers and ignore the 80 pound penalty. 4 motors would be nice but there's only so much room, and only so much you gain in a pull-pull situation.
7  Using Arduino / Project Guidance / Mega 2560 servo pins & Fio AREF on: September 01, 2012, 12:23:57 am
1. What pins are for each timer, to use servos? I'll be putting between 15 and 20 servos on one 2560.

2. To do battery sensing of a 7.4 2S LiPo pack on a FIO, would I just use the analogReference(INTERNAL) and a 25K/10K voltage divider?
8  Using Arduino / Project Guidance / Re: I2C between 8MHZ & 16 MHz arduinos on: August 31, 2012, 10:58:52 pm
Research "open collector".

The I2C pins are open-collector.  They need to be pulled-up so if you external resistors and pull them up to 3.3V they become 3.3V pins.


works for me.
9  Using Arduino / Project Guidance / Re: I2C between 8MHZ & 16 MHz arduinos on: August 31, 2012, 10:51:40 pm
So the 5V signals coming from the 5V board won't overdrive the 3V3 pins?
That's why you use external pull-up resistors.

Doesn't make sense to me, but I'll go with it.
10  Using Arduino / Project Guidance / Re: I2C between 8MHZ & 16 MHz arduinos on: August 31, 2012, 10:43:13 pm
there shouldn't be any issues

level conversion will not be needed, just disable internal pull-up resistors and use external pull-up resistors that "pull" to 3.3V

So the 5V signals coming from the 5V board won't overdrive the 3V3 pins?
11  Using Arduino / Project Guidance / I2C between 8MHZ & 16 MHz arduinos on: August 31, 2012, 09:47:43 pm
Any issues with doing it? Just wondering. Need to link a FIO and a mega over I2C.
Yes I know level conversion will be needed.

(the other end of the xBee link is a FIO & teensy2.0++ pairing..same deal there)
12  Using Arduino / Project Guidance / Re: Add more io on: August 29, 2012, 03:45:02 am
Quote
I can use like 8 tiny's or something
Yes you can, I helped a mate do just this albeit with only 4 slave processors.

OTOH if there are chips designed for this they may be a better option.

Now the next thing to think about is how often do you need the data to be sampled? Can you just sample one motor at a time then move onto the next one and sample that? If so then all you need is a MUX.

______
Rob


That was my other thought. For 66 rotations per second, you can poll the motor for 1/10 of a second, and capture 6.6 rotations. 40-1/10ths of a second is 4 seconds to poll all of them.

If a 4-pole magnet is used, that's 26.4 clicks in 1,600,000 cycles of the CPU. The clock would only capture the 26, so there'd be an error of (26 * 10 * 60) / 4 = 3900 RPM = 100 RPM error.
13  Using Arduino / Project Guidance / Re: Can I use one ground as a reference for multiple inputs? on: August 29, 2012, 03:38:26 am
Instead of tapping into my existing wires, should I just cut them, run one side to input, and then output the value to the gauge? Again, for now I just want to datalog, but eventually I'll get rid of my gauges and switch to an LCD display.

There's been several discussions on the forums on that manner, going to a strictly digital display. I say grab some big LCD's from sparkfun, and go to town! Bonus points if somebody figures out HUD on an arduino.

I thought for a minute, you could play multimeter and use a high impedance to drive the arduino, so that the gauges kind-of [but not really] ignore it's presence. It would take some experimenting, but using your 0-90 water temp as a potential example,

Stock:

Sender @ 0 ohms

Sender @ 45 ohms

Sender @ 90 ohms

A bias resistor has to be used to keep the 0 ohm reading from be a dead short. For 12V operation, a 240 ohm resistor is a half-amp when shorted. Thus,

Sender Link @ 240 ohms

Sender Link @ 285 ohms

Sender Link @ 330 ohms

Now assume the gauge's side of the divider is a 150 ohm:

Vout = (240 / (240 + 150)) * 12 = 7.38 volts

Vout = (285 / 285 + 150)) * 12 = 7.86 volts

Vout = (330 / 330 + 150)) * 12 = 8.25 volts

And so on down the line.


Now for the arduino, you have 2 challenges: Keep the voltage under 5 volts, and not affect the gauges.

To keep the volts down (use 2.56 internal reference), say we use a 10k/50k voltage divider:

Vout = (10 / (50 + 10)) * 12 = 2 volts max

But now that voltage divider is sub-dividing the gauge's divider.

Vout = 240 / (240 + ||150 , 60K||) * 12 = 240 / (240 + 149.62) * 12 = (240 / 389.625) * 12 = 7.39 volts (+0.01 volt change)

Vout = 285 / (285 + ||150, 60K||) * 12 = 285 / (285 + 149.62) * 12 = (285 / 434.62) * 12 = 7.87 volts (+0.01 volt change)

Vout = 330 / (330 + ||150, 60K||) * 12 = 330 / (330 + 149.62) * 12 = (330 / 479.62) * 12 = 8.25 volts (no change)


Again, demonstration only. No idea what the values are in the gauges.
14  Using Arduino / Project Guidance / Re: Add more io on: August 29, 2012, 03:17:12 am
I can use like 8 tiny's or something and then let them calculate for the arduino, how would you suggest to communicate then? Or do you think I should use something else?

I forget what the term is called, but there are IC's out there, designed for quadrature interface, that will count pulses for 4 motors per IC, then you can feed the information from each of those IC's to the arduino over I2C on a request-get method.
15  Using Arduino / Project Guidance / Re: arduino and smartphone to turn on home AC on: August 29, 2012, 03:15:25 am
Do-able? Yes.

Novice level work? My opinion varies from a "Eh, not really" to a very resounding "No", depending on how indepth you want to get.

Perhaps the Treeduino makes a good starting place? http://www.instructables.com/id/Treeduino-The-Web-Controlled-Christmas-Tree/

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