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Sensor to measure a distance! — Parallax Forums

Sensor to measure a distance!

whitefingerwhitefinger Posts: 12
edited 2009-12-31 02:09 in Accessories
Hi I'm new to all this and just need all your opinions on how to resolve my problem please so that i don't buy lots of stuff for nothing! [noparse]:)[/noparse]

Anyway what I'm trying to do is build a device that i will be able to use to measure a long piece of rope that will be at speed!
At first i was looking on google for a measuring wheels but i needed a wheel that was digital and could be plugged into a USB port to retrieve the data into my software!

And some how i have ended up at this site! so i was wondering on building it my self as i can program! so do u have any ideas like do you think i could use the "Reed Switch and Magnet" with the magnet on a wheel so that as the rope passes the wheel, the wheel will turn and then the magnet will pass the sensor every diameter of the wheel and then if i know the diameter in mm then i could work out how long the rope was!!!!!!!!!!!

Comments

  • LeonLeon Posts: 7,620
    edited 2009-07-14 18:19
    That should work. A rotary encoder on the wheel will give you more accurate results - fractions of the wheel diameter - if that is important. You will need a suitable MCU, and software running on the PC. Here is a project of mine that does most of what you need:

    www.leonheller.com/usb

    There are lots of other ways to do it, but they will probably be more expensive and more complicated.

    Leon

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Amateur radio callsign: G1HSM
    Suzuki SV1000S motorcycle

    Post Edited (Leon) : 7/14/2009 6:54:44 PM GMT
  • whitefingerwhitefinger Posts: 12
    edited 2009-07-14 23:51
    Thats great thanks for your quick response i found a rotary encoder from
    http://www.lenord.de/en/produkte/sensorline/01absolut/Agel235/promotion/parametrierung/index.html
    which i hope to use and found a cable wheel reader that i hope to steel the design idea!
    [url=http:// http://www.trumeter.com/home.php?class=Length+Measuring+Systems&app=Cable+and+Wire+Measuring&item=2630&lang=English ] http://www.trumeter.com/home.php?class=Length+Measuring+Systems&app=Cable+and+Wire+Measuring&item=2630&lang=English [/url]
    cheers for your help and any other comment any one else wants to make [noparse]:)[/noparse]
  • whitefingerwhitefinger Posts: 12
    edited 2009-07-17 10:21
    well i was going to buy the above encode until i got a price back of £350 [noparse]:([/noparse]
    anyone know any cheap but good rotary absolute encoders?
  • LeonLeon Posts: 7,620
    edited 2009-07-17 10:29
    You don't need a high precision absolute unit for your application, a much cheaper incremental one should do. What accuracy do you need?

    It's quite easy to make one if you have machining facilities, you just need a disk with holes drilled in it and a couple of opto switches.

    Leon

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Amateur radio callsign: G1HSM
    Suzuki SV1000S motorcycle
  • whitefingerwhitefinger Posts: 12
    edited 2009-07-17 10:59
    well thanks again for your quick response [noparse]:)[/noparse]

    well I'm hoping once creating the above and connecting it to a wheel that will be resting on the 13mm diameter wire rope witch is 100 meters long and when the wire rope passes the wheel the encoder will be able to pass back information to my laptop in meters cm and mm but if it doesn't then i could cope with just meters and cm! [noparse]:)[/noparse]

    to give you some idea on what i do when im not in a recession then here is a video



    thanks again for your responses [noparse]:)[/noparse]
  • LeonLeon Posts: 7,620
    edited 2009-07-17 17:55
    You need to convert the length accuracy to degrees, given the diameter of the wheel. That will give you a value for the resolution you need from the encoder.

    Leon

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Amateur radio callsign: G1HSM
    Suzuki SV1000S motorcycle
  • whitefingerwhitefinger Posts: 12
    edited 2009-07-21 16:22
    Well it looks like i was wrong about the price for that absolute encoder anyway for anyone that was interested as the software to retrieve the measurement was £350 but the encoder was £600. i did say i couldn't afford that and told them my requirements and they also suggested an increment encoder as a cheaper solution to my issue. but as im unemployed im just gona have to wait a while now till i can end my project with the above solution [noparse]:([/noparse]

    www.lenord.de/en/produkte/sensorline/01absolut/Agel235/promotion/parametrierung/index.html
  • SRLMSRLM Posts: 5,045
    edited 2009-07-22 03:27
    You shouldn't have to spend more than $20 (or so) for a home made encoder. As Leon has said, all you need is a disk with regularly spaced holes and an IR LED and receiver pair. Of course, you'll need a microcontroller and a display LCD, but it should be less expensive than a commercial product for reasonable accuracy.
  • whitefingerwhitefinger Posts: 12
    edited 2009-07-22 13:17
    yeah thanks SRLM for kicking my brain in gear, as even tho the cheaper solution wouldnt last 2 minutes in the construction industry at least if i build the cheap solution, i will be able to prove to my boss that it will work and get me boss to pay for the more expensive version so that it will last in the industry! [noparse]:)[/noparse]
  • kwinnkwinn Posts: 8,697
    edited 2009-07-22 13:43
    Cheap doesn't have to mean fragile. A rugged wheel with a slotted metal disk and optical sensor in a sturdy enclosure should be quite durable. They are used in tensile testers that break metal samples involving forces in the hundred thousand to million pound range.

    If you want to build a cheap prototype to test the feasibility use the guts from a mouse. It has everything you need including the USB connection to the computer.
  • whitefingerwhitefinger Posts: 12
    edited 2009-08-03 14:38
    Ok for the people that have been reading this post i just thought i would add this just in case it could help others even through i am finding the read hard going im sure it contains some interesting answers for writing .net code for communicating with usb devises like the mouse that im trying to use to get me measurements for a wheel that is turning!

    thepiratebay.org/torrent/4960955/USB_Complete_The_Developer_s_Guide_4th_Ed_tqw__darksiderg
    the link takes you to a torrent download page to get a free copy! the book is usually £40 in the shop. i hope it helps some one!

    Please note the above link is illegal as you should pay the £40 for it and W9GFO may not like you if you download from it!

    Post Edited (whitefinger) : 8/5/2009 12:22:17 PM GMT
  • W9GFOW9GFO Posts: 4,010
    edited 2009-08-03 19:53
    Is that a legal download? If not, I recommend editing your post to remove the link.

    If it is the author's or publisher's intent to make it available for free via download you should include that information.

    Rich H
  • whitefingerwhitefinger Posts: 12
    edited 2009-08-04 10:46
    well its not a legal download but as its only illegal to upload and not to download or share links i think you will find under the cloudy spectrum of law its ok for me to put the link up as long as it wasn't me who uploaded the file!!!!! but if anyone else is offended by my wanting to help other people that are stuck and wanting deeper information for free then i will remove the link!
  • W9GFOW9GFO Posts: 4,010
    edited 2009-08-04 17:15
    whitefinger said...
    well its not a legal download but as its only illegal to upload and not to download or share links i think you will find under the cloudy spectrum of law its ok for me to put the link up as long as it wasn't me who uploaded the file!!!!! but if anyone else is offended by my wanting to help other people that are stuck and wanting deeper information for free then i will remove the link!

    I doubt you will find that anyone here that is offended by you wanting to offer help.

    I did not mean to say that posting that link was against the law. However, directing people towards a product which was uploaded illegally - and because of that they can now get it for free, is wrong in my opinion. You are participating in the distribution of stolen property.

    I recommended that you remove the link because I think it is in bad to taste to post links for things that you know were ill-gotten.

    Rich H
  • whitefingerwhitefinger Posts: 12
    edited 2009-08-17 11:01
    Right well my level of knowledge has increased by ten fold on electronics in the last month or two which still isn't a lot but im still trying for those that are interested i found this site who is using a old mouse to count the distance traveled but as they say the mouse cant cope with the speeds of there motor! clarkscheff.blogspot.com
    And as my cable that i intend to measure will reach speeds of 50 meters in just a few seconds i feel i need to look else where!
    i am currently looking at syscompdesign.com/lab6.pdf and robotroom.com/Counter.html Which i feel will hopefully get me started just need to get the bread bored and bits! still think im going to have a hard time making it USB capable! does anyone know if you create a USB devise your self if you can just give it your own ProductID and VendorID in which to communicated with your own software or do u have to pay lots of money to the USB people to get ur own unique ID's! I'm sure you can as it would be stupid to pay all that money when u are still at the testing stage?????
  • whitefingerwhitefinger Posts: 12
    edited 2009-08-17 12:58
    The only problem with not really knowing what I'm doing is weather i should be doing robotroom.com/Counter.html which looks really complicated or weather i should just create this which looks easer to develop youtube.com/watch?v=t0HXBEH2BeE&feature=related to interface with the .net software that i have already written!
  • whitefingerwhitefinger Posts: 12
    edited 2009-12-31 02:07
    well after searching the web for an absolute time and never finding what i wanted, me research into the above got quite in depth! so u can imagine how gutted i was when i stumbled on it by accident.
    But nice to see im not mad and that some of my idea are worth creating just like what this person did and beat me to it [noparse]:([/noparse]

    http://www.geomem.com/index.php5?x=catalogue&cmd=viewproduct&id=77#pricing
  • whitefingerwhitefinger Posts: 12
    edited 2009-12-31 02:09
    But on a good note i have looked at his design and believe i can do better [noparse]:)[/noparse]
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