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1  Community / Products and Services / Re: Build Robots and other Gadgets to fit your need, with Android! on: July 24, 2014, 06:34:05 pm
I was a little slow on the uptake but I think it could be a great use to all of the smartphones in desk drawers that have been upgraded.  A lot of processing power and sensors just sitting in the desk drawer.
2  Using Arduino / Networking, Protocols, and Devices / Re: Strange behaviour of Nordic nRF24L01+ 2.4GHz RF module on: July 23, 2014, 06:52:45 pm
I also noticed that removing the aerial altogether allowed transmission at ranges up to 10m or so.

You should never operate a transmitter without an antenna attached.
3  Using Arduino / Project Guidance / Re: Estimating velocity and position on: July 21, 2014, 12:19:46 pm
The first thing I checked was the total acceleration and it was wrong I stopped at that point.  It would be a lot easier to look at the code that was supposed to implement those equations then looking at the output.
4  Using Arduino / Project Guidance / Re: Estimating velocity and position on: July 21, 2014, 09:51:30 am
Quote
By the way Physics is not case dependent, we use upper and lower case letters in equations simply as a matter of choice it does not change the Physics
But what about "g" and "G"?

Those are style decisions that do not affect the physical world at all. There is nothing unique about the meaning of g or G they can be defined to be whatever you want, that is why in technical papers the authors usually are very careful to define any symbols, like g and G, usually the first time they are used, when equations are written any symbols not already clearly defined are defines either right before or after the equation.

wade
5  Using Arduino / Sensors / Re: Developing a water level sensor with TDR. on: July 21, 2014, 09:36:45 am
It is not entirely clear to me what you are describing but a very robust way to measure pulse width is to use a comparator http://en.wikipedia.org/wiki/Comparator to perform the signal conditioning.  Input the signal that you inputted to the o-scope into a comparator with and adjustable threshold.  Connect the output of the comparator to one of the interrupts of the Arduino, initially set the interrupt to trigger on a rising pulse.  The routine (ISR) that is called when the first interrupt is triggered, clears the interrupt, zeroes the clock, delays long enough so the signal is in the nice smooth region, and sets up the interrupt to be triggered on a falling pulse.  When the second interrupt is triggered the ISR will read the clock and this is the pulse width, then turn on the interrupt for the rising pulse to be ready for the next pulse.

It is not as hard as it sounds,
wade
6  Using Arduino / Project Guidance / Re: Estimating velocity and position on: July 21, 2014, 09:25:22 am
The equations you wrote:

velocity = v[k+1] = v[k] + Ta[k]
position = r[k+1] = r[k] + Tv[k]

are approximations for estimating the velocity and position, estimations like this are used when the acceleration of the system is not constant and does not have a closed-form solution.  The equations given by others are used when the acceleration of the system is constant, about the only time acceleration is constant is in a Physics classroom.  v[k+1} is the velocity at the kth + 1 step, likewise a[k] is the acceleration at the kth stepand T is the time increment.

The approximations above are a very crude way to solve for velocity and acceleration, but probably satisfactory for your application as long as T is chosen appropriately.

By the way Physics is not case dependent, we use upper and lower case letters in equations simply as a matter of choice it does not change the Physics.
7  Community / Gigs and Collaborations / Re: Order! Develop module for weather balloon on: July 21, 2014, 09:03:44 am
I just sent you a private message.

wade
8  Using Arduino / Project Guidance / Re: Read a frequency from 0 to 2700Hz with the arduino on: July 16, 2014, 09:23:35 am
At your max frequency of 2700 Hz there would be about 6000 clock cycles between peaks so the processor has more speed than is needed which is a good thing.

If the peaks are well-defined like a square wave input you could attach the signal to one of the interrupts and increment the counter every time the interrupt is triggered.  Use a comparator with a variable threshold if the peaks are not well defined and then attach the output of the comparator to the interrupt pin and count them as defined above.

Hope this helps,
wade
9  Community / Gigs and Collaborations / Re: PCB design support wanted on: July 14, 2014, 03:05:57 pm
I have seen some of Crossroads PCB designs and can say you will get a very good design.
10  Using Arduino / General Electronics / Re: Questions about an amplifier circuit on: July 09, 2014, 05:56:46 pm
I thought I was addressing his questions about the caps and the resistors, so I reread my post and I still think that is what I answered.  I was not answering a question on non-inverting or inverting amps, so your response brings me pause.

11  Using Arduino / General Electronics / Re: Questions about an amplifier circuit on: July 08, 2014, 02:11:22 pm
The first capacitor acts as a blocking cap it blocks the DC component of the signal passing the rapidly varying portion of the signal.  The role R10 is too act as impedance to the rapidly changing signal the cap then provides a path, the DC component of the signal just goes to ground through R10, the value of R10 is arbitrary.
12  Using Arduino / Project Guidance / Re: Sun position calculator - i'm looking for good code to calculate values on: July 04, 2014, 09:12:30 am
One common mistake when using code to estimate angles and such is that the computer generally does it's trig calculations in radians and us humans think about angles in degrees.  Maybe this mistake is not common to the rest of the programming world but for me unfortunately that mistake has been common for me in the last 30 or so years.
13  Topics / Science and Measurement / Re: ph-logger from cheap ph meter from DX on: July 02, 2014, 12:11:43 am
Since it is known that the chip driving the LCD is a ICL7106CM44 why not build a buffer circuit with an Op-Amp which would provide a high impedance input to apply the signals coming from the In-High and In-Low pins (from the datasheet) and read the output of the buffer using the Arduino's ADC, or an external ADC if you want higher resolution. 

Don't get me wrong I applaud AlexShu's solution as he did some very fine work of decoding the output of the LCD driving chip I am just thinking about starting at the other end, the input side of the ICL7106CM44.

wade
14  Using Arduino / Project Guidance / Re: closure logger on: July 01, 2014, 11:02:31 pm

Dave,

Thanks!
15  Community / Gigs and Collaborations / Re: Gig and possible employment opportunity. on: June 30, 2014, 03:06:30 pm
I sent you a PM.

Thanks
wade
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