Making a voltmeter move on it’s own.

Discussion in 'General Electronics Chat' started by Jonlate, Feb 13, 2019.

  1. Jonlate

    Thread Starter Member

    Dec 21, 2017
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    okay, so I didn’t quite know how to word the title and hope the explanation makes more sense.
    As you might know by looking at my other questions, I am in the middle of making a nixie clock, and while my brain works out a few electronic bits, I have turned my attention to the case that will go around it.
    I am looking to do a wooden case, but wanted something a bit more exciting than just plan wood.

    I saw these voltmeters on eBay.
    https://www.ebay.ie/itm/AC-0-300V-R...Meter-Voltmeter-Gauge-Black-W9N5/332732902474
    I think they would look good inserted into the front of the case, but I want the needle to move in a random pattern up and down the scale when the nixie bulbs are turned on.
    However the scale reads from 1-300volts, and I won’t have 300volts (don’t want to have) that amount of voltage floating around.

    So my question is, is there a way I can fool the voltmeter to believe it is getting up to 300v, and is there a circuit I can build that will give the affect that the nixie clock itself is using the voltage and that is why the needle is moving?
    Or if I was to get one that only measured up to 5v, how can I make the needle move?
    I would like the needle to ‘flicker’ around slowly, stay still of a few seconds, slowly rise and fall, etc.

    Any ideas on how I can accomplish this, and what sort of circuit I would need to build?
    The smaller the design the better.

    Thanks again for the excellent brains this site has.
     
  2. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
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    It is a moving coil meter, so the actual meter movement will be low voltage, low current, with a large resistor and diode (it is an AC meter as it stands) in series with the movement. With a bit of care the case can be opened and the resistor and diode removed. Just be aware that there is a fairly powerful magnet in there so while the meter is open make sure no tools can fly in there and damage something.
     
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  3. rsjsouza

    Member

    Apr 21, 2014
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    For the oscillating part of your voltmeter, you can go vintage and try to use a neon bulb oscillator - since you are using Nixie tubes, I suspect you should have somewhere around 100V in your circuit anyways. Simply add a resistor in parallel with the voltmeter (edit) in parallel with the voltmeter's internal resistor to get 1/3 of its resistance so you can get full scale at that voltage.
    Many circuits around the web, but the basic can be found here.
    Other interesting circuits at:
    http://donklipstein.com/sillyne2.html
    http://www.bristolwatch.com/ele/neon.htm
     
    Last edited: Feb 13, 2019
  4. AlbertHall

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    The added resistor would have to be in parallel with the meter's internal resistor not across the meter terminals.
     
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  5. rsjsouza

    Member

    Apr 21, 2014
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    You are absolutely right; I missed that the specified meter is AC.
     
  6. KeepItSimpleStupid

    Distinguished Member

    Mar 4, 2014
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    Since your making a Nixie clock, you ought to be aware of this https://www.daliborfarny.com/projects/ site.

    The guy started a company making high quality Nixie tubes from scratch and he is selling the Zen clock.

    ==

    The meter most likely consists of a meter movement, rectifier and a diode. So, the diode and rectifier get removed and then you have a new problem. You have to find the resistance and sensitivity of the meter without destroying it. 1 uA, 50 uA are common sensitivities.

    You use a series potentiometer and a voltage source to indirectly get the resistance of the meter. With that information, you can convert it to a DC voltmeter using a series resistor.

    It goes something like this. Use a potentiometer at max and guess at the full scale value and a stable voltage source. Adjust the pot, so the meter reads half scale. Measure the voltage across the pot (Vp). Remove the pot and measure the resistance (Rp).

    That resistance of the pot is the meter resistance and I(full scale) = 2 * Vp/Rp

    This isn't a tutorial, but the basic concepts.

    Once you know those numbers, you can set the scale to whatever you want. V(full scale) = (Rm+Rs)*I(full scale)
    Rs is the series resistor you need to add and V (full scale) is what you want.

    Look at www.picaxe.com for a simple processor. You would need a few I2C D/A converters and possible buffers for each meter.
    The processor needs to be able to generate pseudorandom or random numbers.
     
  7. AlbertHall

    AAC Fanatic!

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    1uA would be most uncommon!
    The movement will likely be 100uA to 10mA full scale deflection.
     
  8. MrChips

    Moderator

    Oct 2, 2009
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    Or find a similar meter with your desired range.
     
  9. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    If you were to build a pseudo-random generator with a shift register and connect its outputs to a simple R2R ladder digital to analog circuit, you could get a random voltage to drive your meter. Your application doesn’t need the accuracy, complexity nor multiple D/A chips.

    Here’s a couple of references.

    For generating a random sequence of bits, check these out.

    http://www.cs.miami.edu/home/burt/learning/Csc609.022/random_numbers.html

    https://www.quora.com/How-do-I-build-a-3-bit-pseudo-random-number-generator-circuit-using-logic-ICs

    https://en.m.wikipedia.org/wiki/Linear-feedback_shift_register


    And for an analog D/A using an R2R ladder circuit, check these out.

    https://en.m.wikipedia.org/wiki/Resistor_ladder

    https://www.tek.com/blog/tutorial-digital-analog-conversion-r-2r-dac
     
  10. KeepItSimpleStupid

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  11. Jonlate

    Thread Starter Member

    Dec 21, 2017
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    Okay, so I will start reading the links and get back to you with any more questions I may have.
    I didn’t notice that the linked gauge was AC, but that is just an example of what I want, and what I want to do.
    I would prefer a more vintage style scale, needle, and surround. I have seen some in wooden cases and wonder if I could slip the circuit board for the nixie in with it.

    Another question just came to mind as I typed that. Would the magnetic current(?) force (?) field(?) of the volt meter, affect the nixie circuit in anyway?
    Would it wipe the atemga chip that is used to run the nixie? Would it affect the inductors that are in the circuit?

    Thanks again for pointing me in the right direction.

    Jon
     
  12. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
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    No, No, and no.
     
  13. Jonlate

    Thread Starter Member

    Dec 21, 2017
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    Thank for the brief answer! I only thought it might because if you wipe a magnet across a hard drive it can damage that, and wondered if a programmed atemga chip was the same.

    So back to reading the links and trying to come up with a circuit that gives me a variable oscillating output to feed a volt meter.
     
  14. MisterBill2

    Well-Known Member

    Jan 23, 2018
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    It may be that you will be able to find some nice voltages in the counters in the clock section and be able to use those with a simple D/A converter built from gates and resistors. That would have the meters moving as the clock changes times. If you have a circuit of the clock that you can post we can make some suggestions.
     
  15. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    Why not make them actaully do something like keep the same time the nixie part of the clock does?

     
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  16. MisterBill2

    Well-Known Member

    Jan 23, 2018
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    I have seen such a circuit someplace but I am not sure just where. But that circuit was purely analog. Driving it from D/A converters would be a lot easier. I am not sure if your Nixie clock shows seconds or not, a seconds staircase generator would be a complex beast with 60 steps. Probably another D/A converter is all it would take. And that could be a simple one, just 7 bits binary with reset at 60, if you wanted it to be really accurate. The same as the minutes, while the hours D/a will only need 4 bits. So it can certainly be done, possibly even cheap, with counters and resistors., just like back in 1960. BUT I am thinking that it would be a bit of a challenge for a beginner.
     
  17. Jonlate

    Thread Starter Member

    Dec 21, 2017
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    This is the nixie clock build manuel....
    https://www.nixieclock.biz/Downloads/ClassicNixieClockRev5ConstructionManual.pdf
    Spinnaker....I really like the idea of that analog clock set up. They don’t recommend running nixie clocks all the time to make the tubes last longer, and this will still tell the time while they are off. Howhard it it to get them both to tell the same time?
    Can theyboth use the time chip built into the nixie pcb?
    I must look into how they did this, and what extra it will cost me! If it’s to expensive then I will be back to a self driven random voltage generator.
    Misterbill2.... my clock does have seconds, if that helps.
     
  18. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    No reason why they can't use the same chip, assuming you have enough pins. You will need at least 3 to drive the meters. It would be best if they are dedicated OWM out but no reason they could not be bit banged.

    Where did you buy the tubes? I want to eventually make such a project.

    My neighbor told me he used to have boxes of them brand new at work. He tells me they were likely thrown out :(
     
  19. Jonlate

    Thread Starter Member

    Dec 21, 2017
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    What a shame to throw them out!! I suppose to some people they are just glass tubes and they don’t know what they do.
    I brought mine off eBay, but did loads of research on what the best tubes were for me. I was surprised that the life span differs so much, as does build quality. And I also didn’t like the look of the number 2 being a upside down number 5 in some tubes (or is that the other way around)
    Really though it depends on what you want and how you want your case to look.
    Do you want side view ones (look like small glasss bottles) or top view ones(look like tealights) or VFD ones are becoming more popular (think calculator digits)

    I have zm1040’s that are side view, but am building cup system, like napkin rings with solid backs, to mount them in and to hide the wires.
    I want to get some z5700m which are side view for this multimeter/ analogue clock set up I am asking about now.
    And I have a board on order to build a VFD one next!!

    Its all good fun
     
  20. Jonlate

    Thread Starter Member

    Dec 21, 2017
    64
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    Just another very quick question.....
    If I want to make these move like a clock, is it best to get a voltage one or a amp one?
    Which one will be easiest to modify?
    Thanks
     
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