LED Ohm resistance reader help

Discussion in 'The Projects Forum' started by lostintranslation, Nov 19, 2013.

  1. lostintranslation

    Thread Starter Member

    Nov 6, 2013
    37
    0
    I have an LED ohms resistance reader, that reads to the tenth decimal place 00.0 it is up to 200 ohm, but I would like to be able to read down to the hundredth and more accurately. Is there any way to get the decimal place to the hundredth 0.00 by adding in a resistor to the board? or anything? In a perfect world reading from 0.00-9.99 would be ideal. it seems like a very hard part to find, and wouldn't even mind being able to DIY my own if need be. thanks in advance for any insight and help, it is appreciated.
     
  2. #12

    Expert

    Nov 30, 2010
    16,261
    6,767
    I did one of those a couple of months ago. It's in the finished project section. Some people say you can do it with an LM317 chip, too. The critical point is calibrating the current to .0100 amps. The better the calibration, the better the results.

    http://forum.allaboutcircuits.com/showthread.php?t=89321
     
  3. lostintranslation

    Thread Starter Member

    Nov 6, 2013
    37
    0
    far out. thank you. it's going to take me while to translate that into action, but very cool, it's a start. I'm pretty visual oriented, graphic artist by trade, so most of the tech takes me a while to pick up on, once I see it wired, it helps tremendously. I would just buy off the shelf, but there really aren't many good options out there for low ohms resistance reading. thanks again, cheers.
     
  4. wayneh

    Expert

    Sep 9, 2010
    12,094
    3,033
    It may be worth asking WHY you (a graphic artist) want such a device. Perhaps there is an easier way to accomplish your chore, and some clever person here will see the simple solution.
     
  5. #12

    Expert

    Nov 30, 2010
    16,261
    6,767
    The beauty of the 10 ma circuit is that it won't melt things like the 1 amp current driver also in the finished projects section. 10 ma is just barely and exactly what will fit your request. Calibrating to .001 ohm might be possible, but the meter required to do that kind of quality is (probably) outside the price range of an amateur.
     
  6. lostintranslation

    Thread Starter Member

    Nov 6, 2013
    37
    0
    thanks, this is on a budget for sure. I have and LED display that reads my ohms resistance down to the tenth, but I'm trying to get it reading down to the hundredth if possible. as to the why I want such a device, I build resistance coils that I want to be able to gauge from 0-9.99 ohms with a digital LED. The higher ohms aren't as critical they be accurate as are the ohm under about .7 or so. those need to be more accurate the lower they go.
     
  7. tracecom

    AAC Fanatic!

    Apr 16, 2010
    3,869
    1,393
    Kanthal and/or nichrome vaporizer coils?
     
  8. lostintranslation

    Thread Starter Member

    Nov 6, 2013
    37
    0
    and/or is correct. both or either. they work much the same way.
     
  9. tracecom

    AAC Fanatic!

    Apr 16, 2010
    3,869
    1,393
    Can you solder?

    Can you solder surface mount parts like the one shown in pictures in the thread #12 linked to?
     
  10. lostintranslation

    Thread Starter Member

    Nov 6, 2013
    37
    0
    yep, i can solder, it's improving as I go, need to improve my my tools and techniques, but it's getting there. pretty much if I see it I can get, figuring out this stuff through reverse engineering is kinda how I pick up on this, no offense meant to anyone, I am not an engineer nor do I play one on TV...
     
  11. lostintranslation

    Thread Starter Member

    Nov 6, 2013
    37
    0
  12. tracecom

    AAC Fanatic!

    Apr 16, 2010
    3,869
    1,393
    Here are my last nosy questions. Do you have a digital multimeter? What kind is it?
     
  13. #12

    Expert

    Nov 30, 2010
    16,261
    6,767
    Warning: The device that tracecom and I conspired to build must be measured with a voltmeter. It will NOT drive an ohm meter.

    Did I mislead you? Like you thinking I sent you to a circuit that will work with an ohm meter?
     
  14. lostintranslation

    Thread Starter Member

    Nov 6, 2013
    37
    0
    i didn't have enough time to begin to digest the device link posted, so no worries, but thanks. conspired sounds ominous...lol

    And it's not nosy, it's helpful as far as I can tell. I use a couple different mostly junk cheap multi meters, but I don't really have an issue with figuring out that they both have some resistance built into the leads and have a natural margin of error due to their cost/build quality, I just touch the leads together for the reading, and then subtract whatever the meter reads from the resistance I have reading on the coil. so if the leads touched together say .7 ohms, and the coil reads 1.5 ohms when tested/probed, it is a .8 coil. ? pretty sure anyways.
     
  15. #12

    Expert

    Nov 30, 2010
    16,261
    6,767
    Yep. It works that way. It's called nulling the zero. You can do it mentally. My meter has a nulling function built in.
     
  16. lostintranslation

    Thread Starter Member

    Nov 6, 2013
    37
    0
    that is how I've been doing it. but i put this LED 200ohm one together and it is only off .2 ohms, which is less off than the multi meters I use are. I would just like to have one that reads the hundredths, so is it possible to get this LED ohm reader that I have (0-200 ohm) to read to the hundredth or is there an LED ohm meter out there that would read 0-9.99 ohms, or even 0-19.99 ohms plus or minus whatever the margin error is?

    I know they exist out there, but most of the ones out there are a crap shoot of overpriced junk. I can't find just the LED ohm meter that will do 0-9.99. you know the old saying, if you want it done right....figure out the circuit? i don't mind making it work, but would be thrilled with already works...
     
  17. #12

    Expert

    Nov 30, 2010
    16,261
    6,767
    My meter cost $300 in 1978. Guess what it costs now!:eek:
    and it will not read to .01 ohms.

    That's why we designed the 10 ma converter. It boosts the range on a $300 meter for less than $10.
     
  18. lostintranslation

    Thread Starter Member

    Nov 6, 2013
    37
    0
    also have a LED resistance reader that I grabbed thinking it would be right, but it is 0-20kohm, not 0-20ohm, (yeah I missed the K part, didn't I) so chalk up another one for late night buying sprees on Ebay...
     
  19. lostintranslation

    Thread Starter Member

    Nov 6, 2013
    37
    0
    1978 was good year, I think they call that vintage these days. lol.

    yeah, I'm not looking for "exact" per say, well, not thousands or even hundreds of dollars exact anyways, just trying to cobble something together.
     
  20. #12

    Expert

    Nov 30, 2010
    16,261
    6,767
    As I said, it all comes down to calibration. If you can set the 25 turn potentiometer to 10.00 milliamps and use the Kelvin connection properly, it will read .01 ohms on a voltmeter set to the 200 millivolt scale without breaking a sweat.
     
Loading...