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question about multimeter

Discussion in 'General Electronics Discussion' started by Neight, Mar 28, 2011.

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  1. Neight

    Neight

    18
    0
    Mar 28, 2011
    ok, i know this is going to be a dumb question, but i would really just like clarification.
    I have made a circuit and am testing it with a multimeter. to check volts i have to set it to the 200m setting to get a reading on the display. the display is reading 22.5. what exactly is this telling me.
    sorry for the noob question, but i am very new to electronics and had to borrow the meter to have one to use.
    if it helps, i am making a circuit to pull Rf and turn it into electricity. sort of a crystal radio without the radio part. i have put the circuit together right, and am trying to test how much power it makes. i am not expecting much, but i don't know what the number on the display translates into for actual power output. anyone who can help me clarify this would be enormously appreciated.
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,386
    2,772
    Jan 21, 2010
    In the voltage range, 200m means that your digital multimeter will read up to something like 199.9mV. A display of 22.5 therefore indicates 22.5mV (22.5 thousandths of a volt).

    If your meter has an input impedance of 1Mohm (which is typical) then you are currently harvesting a power of 5 x 10^-10 watts (0.5nW, or about one half of a billionth of a watt)
     
  3. Neight

    Neight

    18
    0
    Mar 28, 2011
    excellent, that answers my question perfectly!!
    so far, if i let it sit and charge up the capacitors for a little while, i have gotten up to 4.2 volts, but it takes a while to charge up that high and is nearly instantly discharged when i put a load on it (piezo buzzer). I am guessing this is because i used silicone rectifier diodes instead of the Ge 1n34's that the instructions called for. unfortunately radio shack doesn't carry the Ge diodes anymore so i will have to order those to test my theory
    thank you so much for the answer, that is what i suspected, but wanted to make sure. it takes minimum 4 volts to get a tone from the buzzer, and i wasn't getting noise. wasn't sure if i did something wrong or i just wasn't meeting minimum power. once i let it sit long enough, i got a very short dying tone from the buzzer. will have to play more, having a blast learning so far!!

    quick side question, any idea why when i put the multimeter to test ohms on the same circuit, it charges up much much faster?
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,386
    2,772
    Jan 21, 2010
    Yes, the power available to charge the capacitor is very low. The peak voltage may well be several volts (or even higher). However the capacitor also leaks some charge, and at some point the peak voltages coming from the rectifier do not have enough energy to exceed the internal discharge due to leakage.

    Yes, the power required to drive the buzzer is much higher than your receiver is constantly receiving. Once it uses the power stored in the capacitor, the receiver can not supply enough to keep it buzzing.

    It probably does not make much difference. A germanium diode would increase the voltage you're seeing by perhaps 0.5 volts. It may also allow you to see slightly faster charging. But it won't supply substantially more power. You could also try using a very low voltage drop schottky diode. I have some with *very* low forward voltage drops. I doubt that it would help though.

    A longer antenna and a good earth will be of great assistance.

    Yes, you can think of the capacitor as a small battery that you're charging up. You could select a capacitor with a higher capacitance. It would operate the buzzer longer, but take proportionately longer to charge.

    That's because the meter is charging the capacitor. Meters supply power in order to measure resistance.
     
  5. Neight

    Neight

    18
    0
    Mar 28, 2011
    you are a wealth of knowledge and i appreciate you brother :)
    i am learning, though the internet can be a sketchy place to find accurate information. very glad i found this forum, it has already been enormously helpful.

    would adding a transformer to the mix help with the power storage or slow the discharge at all, or do i have the wrong idea about transformers? (are they more than meets the eye? honestly, i had too, one of my favorite cartoons as a kid :p)
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,386
    2,772
    Jan 21, 2010
    A transformer would not help a great deal. In essence, your tuning coil is one half of a transformer that is being linked with the other half at the radio transmitter.

    The problem you have is not so much related to a voltage mismatch as it is to the infinitesimal amount of power that you can get this way.

    As I said, good antenna and good earth will be your first best steps. I imagine you have a reasonable antenna (and maybe earth) at the moment to get the amount of power you're getting.

    OK, there is one other thing you could do... Move close to a transmitter. As you halve your distance, the power you can get will be four times greater.
     
  7. Neight

    Neight

    18
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    Mar 28, 2011
    lol, at the moment my antenna is a coil of house wire that i pulled off an electromagnet i made a few days ago. right now i do not have this circuit grounded, it is just hooked up at the antenna end and hooked to the multimeter at the other end. i need to make another bit of this to attach a ground wire, but currently am out of parts. will be ordering more so i can build it up a bit more and put a proper antenna on it, but all things in good time. right now i am just having fun playing around and learning what i can.
    thanks a ton for the advice, hopefully soon i can be asking less basic questions and getting into this a bit deeper, but we all start somewhere right? :)
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,386
    2,772
    Jan 21, 2010
    We do, and this is as good a place as anywhere :)
     
  9. Neight

    Neight

    18
    0
    Mar 28, 2011
    sadly, so far i know nothing of building circuitry. only reason i have gotten anywhere with this at all is because i was able to solder the parts directly to each other. i took my parts to a buddy's house who has a breadboard and limited knowledge and got it to work, so then i came home and soldered it together. it's not pretty but it works and i am quite happy with at least that much progress. i need to get some books and actually learn what i am doing, but at least these kinds of components are cheap and easy to come by, lets me tinker without knowing what i am really doing.
    your help has been enormous and at least pointed me in the right place to take my next step while i am learning the rest.
    PROGRESS!!
     
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,386
    2,772
    Jan 21, 2010
    If I were you, my next task would be to draw a circuit diagram of what you have built. (You may have started with one) This is the way that we communicate electronic designs and being able t draw, read, and understand then (even a simple one) will help you a great deal.

    If you can, show us a photo of your first project. Always good to see!

    Next you can learn how its actually working and that may help you to understand how to make it work better.
     
  11. Neight

    Neight

    18
    0
    Mar 28, 2011
    ok, here is a photo of the circuit. the aligator clips are the antenna. i had an AC to DC converter that went bad that had the clips on it, i cut off the bad end and used to clips to connect my home made antenna wire to the circuit. sort of rigged, but it works for now :)

    the diagram that is also attached is the one i drew, but i had it to start off with. sorry the diagram is a bit crude, i am not very good with adobe illustrator, so that's the best it gets for now.

    from what i can tell, this is basically a simple transformer in the circuit, with two series of capacitors acting as the windings and the diodes directing the charge. i am sure there is a more accurate way of describing it, but that is about as much as i can tell from the initial drawing. the circuit in the photo is upside down, which is why the diode's are backwards to the drawing. I more or less understand what this circuit is doing with the current, even if i can't explain it very well.

    i would like to make a duplicate of this circuit and hook another wire to it that will go to the ground, which as you said, should improve it's function.
    hope all this makes some sense, i am not the best with descriptions, though it all makes sense in my head so far :p
     

    Attached Files:

  12. Neight

    Neight

    18
    0
    Mar 28, 2011
    the original instructions that i started with called for 100µF 50v electrolytic capacitors, but radio shack only had 100µF 35V capacitors.
    also the diodes are supposed to be 1n34 for the lower end Rf signals and lower forward voltage drop, but again, radio shack doesn't carry Ge diodes anymore,
    so i just picked up some silicon 1n4004's to see if i could make it work. i plan on ordering some parts online soon and making two of
    these to put together with the proper parts and ground it as well as adding a longer and better antenna and seeing where it goes from here :)

    the components i have seem to work well enough, but i will get the one's originally called for just to see if there is a noticeable difference in
    performance.
    thanks again for all you help, and if you have any other suggestions for me, i will gladly take them. i have learned a lot here tonight!!
     
    Last edited: Mar 28, 2011
  13. Neight

    Neight

    18
    0
    Mar 28, 2011
    what would be the best way to ground the circuit i have pictured in my post above. the only video i have seen of this circuit being grounded actually had two of these put end to end and one end was connected to the antenna and the other end was connected to the ground and they were attached in the middle, like a mirror image. is there a place on this one circuit that i could attach a ground wire or should i go ahead and build a second circuit and ground the whole thing that way?
    I have sunk a long steel plate (actually the blade of a broken decorative sword) a few feet into the ground and attached a wire to various places in the circuit and haven't gotten any noticeable results. i know i need a better antenna, which will help, but for right now i am just looking for a good way to ground this circuit to see what kind of difference it makes. if there is no better way to do it than making a second identical circuit and grounding it that way, that is fine, that is actually what i am expecting. i just want to make sure i am not missing anything at this point.

    if clarification is needed on my explanation, i can try and draw up a few diagrams on what i am talking about. my written communication skills leave a bit to be desired at this point, which i hope to improve as i learn more of what i am doing :)
     
  14. Neight

    Neight

    18
    0
    Mar 28, 2011
    ok, after a bit of experimentation, i have seen some change. i connected my ground (sword blade) to the negative terminal of my circuit. it built up to a max of just under 1V (.889) which drops very quickly when i put the meter on it. that is a bit higher than i got when i had no ground, but not much better. with the meter "charging" the capacitors it will go up to 4V max charge.
    if anyone can see a way to add efficiency to the system or make it a bit more sustainable, i am more than willing to learn. any links to good websites to look at, or just info that i am missing in general would be great!!
     
  15. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    You don't need 2 & 2 ceramics in series, making four in total, you only need two in all.
    Ground is supposed to be connected to the center (between the two electrolytics).
    Use 1N4148's instead of 1N4004's, at least they'll work at higher frequencies.
    The efficiency lies with the antenna, "sustainability" with the electrolytics.
    This circuit will pick up mains hum from the house wiring, as well as RF.

    Save circuit diagrams as PNG or GIF instead of JPG btw..
     

    Attached Files:

  16. Neight

    Neight

    18
    0
    Mar 28, 2011
    excellent. thank you very much!
    the original plans called for 2 - .2µF 50V ceramic capacitors, which i set out to get, but again radio shack seems to be fail for a good source of electronics these days, and didn't have them. i happened to see a video of a fella making one of these and he used the 4 - .1µF 50V capacitors, and i found those at radio shack, so i wired it the same way, but you are correct the original plan called for only two.
    as far as the diodes, i know nothing of diode part numbers, so i just grabbed a few that sounded like they would foot the bill, thanks for the suggestion, in the end i will order some 1n34's online, but for now this is giving me data to play with for the future.
    very interesting that it will pick up the hum from mains, i did not know that. i am learning, however slow, it's still progress :)
    thanks a ton for the info, got it wrote down and will put it to good use.
    (and i will make sure to save the diagrams in the proper format from now on)
     
  17. Neight

    Neight

    18
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    Mar 28, 2011
    update!
    i moved my ground connection to in between my electrolytic as suggested and let it charge up a little while and got about another .1V built up so far, so it has made a bit of a difference. sort of seems self evident at this point, not sure why i didn't see it earlier, but sometimes i over think things :p
    thanks for the suggestion, it's working!
     
  18. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Ok, I see. You can make a 0.2µF cap out of two 0.1µF cap's but then you must put them in parallell, not in series. At RF the exact capacitance won't matter though.
    At mains frequencies it might matter, but still the size of the antenna and its placement matters most (even more than where ground is connected to the circuit).
    GIF & PNG are "lossless" and won't introduce dots & artefacts around the graphics. They even end up being smaller than JPG files because they keep it "clean".
     
  19. Neight

    Neight

    18
    0
    Mar 28, 2011
    yeah, in the next couple of day i hope to be able to order some parts online and actually follow the original instructions, so i can see what the difference is, and maybe understand how this is all working better.
    right now i am looking into Tesla radiant energy, it's very interesting, but a difficult place to start learning. sort of like jumping into the very deep end of the pool to learn how to swim, but i feel like i am picking it up pretty quick for a complete beginner :)
    and this forum has been incredible so far, i have learned a lot and am progressing much faster cause of all the help on here, so thank you very much to both *steve* and Resqueline for your suggestions and explanations!! you have my upmost appreciateion :)
     
  20. Neight

    Neight

    18
    0
    Mar 28, 2011
    quick update
    i changed my circuit to have the ceramic caps in parallel and added 2 1000µF 35V electrolytic caps to it as well. it has made a difference, the caps charge much faster up to about .5V where it slows down a bit. also it tends to charge higher, about 1.5V - 2V is average, with a high of nearly 6V (only once and there was a baby monitor on nearby, with music coming from it, so i am assuming that was likely the source of the higher voltage). when i put my buzzer to it to discharge, i get a significantly longer tone as well.
    I just want to say thanks again, i can't tell you how much help you guys have been already. i am learning a whole lot, now that i know better what i am looking at!
    (sorry if you are all not quite as interested as i am, i am a very enthusiastic beginner, so it's all still new to me :p )
     
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