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1  Using Arduino / Project Guidance / Re: Speed Sensing. on: September 17, 2014, 11:16:23 am
2  Using Arduino / Project Guidance / Re: Newby that wants to build an agv on: September 15, 2014, 07:12:17 pm
There's also a problem when returning to the line. If you hit it at 90o, which way do you turn?

I always turn the wrong way!
3  Using Arduino / Sensors / Re: Bike Tire Pressure on: September 03, 2014, 12:20:41 pm
At first I thought mounting the sensor inside the tube and then an RF transmitter to a receiver on the handlebars, but there is probably a simpler solution.

Make a device that attaches to the valve stem and mount the unit to the rim, when the pressure is below a threshold an LED could be turned on.  Simpler yet use an old fashioned tire presure gauge at the beginning of the ride.

Hope this helps,
4  Community / Gigs and Collaborations / Re: Help and get reward .... on: August 27, 2014, 02:20:59 pm
Wow!  I can get a whole $50 to sell out what a deal! 

Then you get a certificate that states you are qualified to do something that you have demonstrated you can't do because you cheated to get the certificate.  Maybe the certificate gets you a job at a company designing say pacemakers, and you screw that up, because you don't deserve that certificate, and people die.

You are willing to pay me a whole $50 to help you on this path.  You may be smart enough to understand what my response is, but then you probably aren't so I will state it clearly: NO!!

I could direct you to the nearest fastfood restaurant for a job application, you will screw up there but I don't eat fastfood so I don't worry.
5  Using Arduino / Sensors / Re: Gun trigger force sensor on: August 24, 2014, 10:20:39 am
Look for strain gages they come in sizes from large to very small and in general are very reproducible and accurate.

6  Using Arduino / Project Guidance / Re: Detect beeping sound on: August 24, 2014, 10:18:15 am
The LM567 would probably work quite well for your application if you know the frequency of the beeping tone, you could do this a variety of ways try to find the frequency:
- look at the beeper to see if they have a frequency of the output on the device or datasheet
- use a microphone and an amplifier (the amp will probably be needed if you are using the LM567) and drive the output of the amp and input that into an oscilloscope either a traditional one or a USB scope.  Once the beep signal is on the oscilloscope you can find the fundamental freq.
- use a variety of the frequency transform algorithms available to the arduino and input the amped signal into an analog pin on arduino this analysis should show what the fundamental frequency of the beeper is.

Now that you have the fundamental frequency you can tune the LM567 to that frequency and measure the output of the LM567 and that will be proportional to the strength of the sound at the fundamental frequency.

Doing it this way arduino is not doing any DSP that is all being done by the $2.00 LM567.

Hope this helps,
7  Using Arduino / Sensors / Re: Sound sensor on: August 21, 2014, 03:58:19 pm
The web is a vast warehouse of information on FFT's and google is a pretty amazing guide to find your way around.  In a nutshell an FFT will take the meausrements you have made in the time domain and transform that into the frequency domain allowing you to easily measure the signal strength at given frequencies instead of at given times.

Google will find you far more detailed information than any of us has time to write down in a forum reply.  The best thing you can learn from this exercise is that Google is your friend.

Good luck,
8  Using Arduino / Networking, Protocols, and Devices / Re: Increase Range of RF devices on: August 02, 2014, 07:02:47 pm
RF does not penetrate water very well for practical purposes for the hobbyist it does not penetrate at all.  This topic comes up periodically and usually the person who asked it was not aware of that because it seems so easy, but it is not.  When they talk about low frequency radios used for communicating with submarines they are talking much below 300 MHz, they call it extremely low frequency and use antennas that stretch for miles.

9  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.
10  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.
11  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.
12  Using Arduino / Project Guidance / Re: Estimating velocity and position on: July 21, 2014, 09:51:30 am
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.

13  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 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,
14  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.
15  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.

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