Pages: 1 [2] 3   Go Down
Author Topic: Help me decide please.  (Read 2653 times)
0 Members and 1 Guest are viewing this topic.
Offline Offline
Newbie
*
Karma: 0
Posts: 8
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

The photocell wont distinguish between light from your experiment and the light in the room. (I assume you aren't doing this in a photographic dark room.) So you need to make sure it isn't affected by changes in the level of light in the room.
Logged

Global Moderator
UK
Offline Offline
Brattain Member
*****
Karma: 238
Posts: 24353
I don't think you connected the grounds, Dave.
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

You'll also need to account for variations in the brightness of the source.
Old CD-ROM drives can often provide tiny half-silvered mirrors ideal for this purpose.
Logged

"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

Offline Offline
Newbie
*
Karma: 0
Posts: 22
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Oh is that so? Not Again!

Hmm maybe i would have to capture this problem mechanically by placing it very close to the wheel with minimal distance and enclose it three sides exposing just the wheel surface on one side. I will have to figure it out. Also I just now had a word with my friend about the problem of using UltraSonic. He suggested increasing the processing power might help with getting nanoSeconds. He said Arduino Operates at 16 Mhz and maybe choosing a processor with more 700 mhz will be a safe bet. And he gave the name beagleboard to start thinking in those lines. But i am not sure as i searched over internet. What i need is time elapsed between two events in nano seconds. With ATmega328 running at 62.5ns for an instruction it is only possible to detect events in microseconds.

It i get the value in nanoseconds, i would have been happy to use ultrasonic and plot the graph because the analysis of the graph is made in the computer and not in the circuit. So there are two directions for me now. One is Light Scattering and the other one is switching to an high power processor which can have registers to store nanosecond length values.

Now wondering which will yield results soon as the timeline is very less.

Regards,

Ashok Srinivasan.
Logged

Dubuque, Iowa, USA
Offline Offline
Edison Member
*
Karma: 30
Posts: 2244
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

If you're considering other options this could also be done with a piezo sensor. The implementation would be similar to how the needle on a record player works.
Logged

Global Moderator
UK
Offline Offline
Brattain Member
*****
Karma: 238
Posts: 24353
I don't think you connected the grounds, Dave.
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

ultrasonic transducers have mass.
Mass that has to be accelerated.
Good luck on getting nanosecond resolution on them.
Logged

"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

Offline Offline
Newbie
*
Karma: 0
Posts: 22
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Hello Dear Friends,

I stumbled upon something today. Since you guys saved me from a lot of headache with all your information. I started looking out for the right directions.

Now the situation holds such that i will use the photocell method. I am yet to receive the board in my hands. Also i have another idea(might be stupid). Since Arduino can communicate with Java, is it possible to notify pulse sent and pulse received to Java as two separate events to a custom written Java Front end via USB? In that case we can note the time in nano seconds using System.nanoTime? for my laptop has a better processing power and can support nanosecond resolution i guess! I checked that function and it works fairly consistent.

In this case are there any factors that might stop the pc from listening to the events in an uniform time delay?

If someone thinks i am pondering over an impossibility please forgive me for i am just trying to figure out a solution with the limited knowledge that my little brain possesses. 
Logged

Global Moderator
UK
Offline Offline
Brattain Member
*****
Karma: 238
Posts: 24353
I don't think you connected the grounds, Dave.
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Java and nanosecond are not words I would normally expect in the same sentence.
Logged

"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

Offline Offline
Newbie
*
Karma: 0
Posts: 8
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Not to mention the delay from still using the arduino. Perhaps some bespoke ADC could manage such quick responses, but I think you'll have to do a fair bit of research into ultrasonics control... perhaps see if you can find something like Ultrasonics by Ensminger in a library you have access to.
Logged

New Jersey
Offline Offline
Faraday Member
**
Karma: 48
Posts: 3417
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Google ultrasonic roughness measurement.

I came across some references suggesting that it is a viable technicque. The method seems to revolve around measuring how much the surface scatters the utrasound source. Sadly, most of the pages I've seen so far handwave over how the measurement and subsequent analysis is done, but the suggestion in the OP may be viable - it just looks like most of what I saw was proposals, not working examples. 
Logged

Global Moderator
UK
Offline Offline
Brattain Member
*****
Karma: 238
Posts: 24353
I don't think you connected the grounds, Dave.
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

However it is done, it is not going to be with an Arduino and Murata-style transducers.
More likely the sort of transducer you find in a medical ultrasound device, which operate at much higher frequencies.
Logged

"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

Offline Offline
Newbie
*
Karma: 0
Posts: 22
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Hello all,

Now that the first problem i asked for(actually this is supposed to be the least of the problems) is solved, i am now looking at the primary problem which most of you tried to make me understand in the initial stages itself.

I had been searching for higher frequency ultrasound sensors but i do not see anything that is configurable like the Ping. But Ping being configurable easily, still 40Khz frequency it supports is not sufficient. Like AWOL mentioned in the start of the thread itself this sensor will produce a beam of 8mm width. Since it took some time for me to figure out this problem(better late than never ;-) ), I finally understood i was missing the point all this time. Meanwhile i am now working on the photocell method.

What is wish to ask for is that are there sensors available with frequencies >= 40MHz ? Since cost will not be an issue but how far they can be used with microcontroller boards will be a factor that needs to be considered. If in case someone comes across ultrasound sensors with higher frequencies available, kindly do let me know.  If the sensors are available, and depending on the safe range of distance it can travel, the mechanical design can be changed by placing it very near to the wheel and ensuring it is not in contact with the subject.

BTW i have some links related to UltraSound which i guess might be useful for someone else is given below.

KHZ -> MHZ conversion = http://www.unitconversion.org/frequency-wavelength/kilohertz-to-megahertz-conversion.html

Ultrasound Wavelength Calculator = http://users.tpg.com.au/mcgrath_/Calculators/Wavelength_Calculator.htm


Thanks in advance.

Regards,

Ashok Srinivasan.

Logged

0
Offline Offline
Newbie
*
Karma: 0
Posts: 10
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I realize you have moved on from your original problem, but given this is a software improvement, you might consider it down the track...
I came across a paper some years back that addressed the problem you are trying to do, except they were mapping 2 surfaces at once (inside and outside surface of the cornea) to make a 3d model.  I think they took readings with an accuracy of 15 um and by using several readings and some very cleaver math got their accuracy down to 3um.  I'm not sure if the paper I am thinking of is still available now that their company was bought out but google "measure corneal topography" or "Orbscan" as their math might be relevant to your project and should give you some crazy accuracy.
Logged

Offline Offline
Newbie
*
Karma: 0
Posts: 22
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Thank you Flyboy and KE7,

I have started looking in the three directions. Each day it is a good learning curve. I started with Arduino without any idea of electronics. Now i am getting used to learning stuffs which is giving me a fair idea of things around me. Thank you guys for having enlightened me. Will be posting my progress in this thread. In short this is really exciting.

Regards,

Ashok Srinivasan.
Logged

Offline Offline
Newbie
*
Karma: 0
Posts: 22
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Hello Guys,

I am back. Life's been really really interesting since the advent of ultrasound. I have a question here. Can someone tell me if i can measure the amplitude or the strength of the echo from the ping sensor? Or are there sensors out there in the market that gives a provision to measure the amplitude other than the time of flight?

Regards,

Ashok Srinivasan.
Logged

Global Moderator
UK
Offline Offline
Brattain Member
*****
Karma: 238
Posts: 24353
I don't think you connected the grounds, Dave.
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Quote
Can someone tell me if i can measure the amplitude or the strength of the echo from the ping sensor?
No, that isn't possible directly.
Quote
Or are there sensors out there in the market that gives a provision to measure the amplitude other than the time of flight?
Yes, they're called oscilloscopes.
Logged

"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

Pages: 1 [2] 3   Go Up
Jump to: