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FAO Paul Grohe RE building a Microgram scale

Prodigy 50 points

Replies: 39

Views: 12399

Hi Paul, I saw your amazing YouTube video: http://m.youtube.com/#/watch?v=n90whRO-ypE&desktop_uri=%2Fwatch%3Fv%3Dn90whRO-ypE

...showing you can accurately weigh an Eyelash hair. I am carrying out a study for an international Conference for Eyelash Extension professionals and have been searching everywhere on how to accurately weigh various combinations of individual Eyelash Extentions. Can you advise me on how I could access something like that? Even to hire or something? My partner is a Electrical engineer so he should be able to help but any advice would be grately appreciated.

The forum that I post on for Eyelash professionals were even considering pitching together to buy a suitable scale (to answer our many questions about this for Natural lash safety) but they're extremely expensive from what I've heard.

Any advice you ( or anyone else) has I would be most grateful.

39 Replies

  • Gee,

    Amazing? "Reality TV" and Infomercials has really shrunk our expectations of "Amazing"...

    Being so close to April Fools, I don't know if I should take this seriously! :)

    We do not get a lot of traffic from the Eyelash Extension Professionals crowd on our E2E community...I expected more questions from South America asking how to weigh "sugar"...

    I'm not that clever. The original idea of using a meter movement originally came from a pair of 1996 and 2001 articles in Scientific American by Shawn Carlson. George Schmermund came up with the original idea to use a surplus galvanometer movement as a microgram scale and Shawn Carlson wrote an article for Scientific American.

    The scale "breadboard":

     http://www.erowid.org/archive/rhodium/chemistry/equipment/scale.html

    and Mr. Carlson refined it with optical sensing in his second article:

     http://www.scientificamerican.com/article.cfm?id=down-among-the-micrograms

    My scale is just a refinement of the optical sensor principle, as well as adding the back-end analog VGA's, A/D's and processor. It was literally built with junk-box components.

    The meter movement is from a 5 inch 'edge-wise' industrial process meter. The "tray" is just the pointer turned sideways. These meters are still available through various electronics surplus houses. Most meter movements are only good for a few milligrams. The optical detector is a standard HP optical slot detector.

    Unfortunately, the main device I built the scale to demo is now obsolete (LMP8100), and time has not allowed me to update it with something more current.

    If your partner is a EE, he should easily be able to duplicate the articles.

    You can get milligram foil weight sets for calibration. They are just little pieces of thin stainless steel trimmed to the correct weight. Google "milligram calibration weights". You will need at least a 1mg weight.

    I hope this helps ease the burden of overweight eyelashes around the world...and will lead to lighter, trimmer lashes...Tammy Faye will rejoice.

    Regards,

    Regards,

    Paul Grohe

    TI Comparators (CMPS) Applications Group

  • In reply to Paul Grohe:

    Hi Paul

    Many thanks for the prompt response!

    I promise this is real  - I am an Eyelash extension professional carrying out research and I'm no fan of realty TV ;)

    Ok, so I have my shopping list and have been badgering my partner with questions, so I'll be buying:

    - HP optical slot detector - this I'm having great difficulty finding (I'm based in the UK), they only appear to be available in bulk fom the US

    - Millivoltmeter - still searching

    - 1 mg Calibration Weight - I've found THIS 1mg F1 Class Calibration Weight

    - Galvanometer - I've found THIS PHILIP HARRIS LTD VINTAGE GALVANOMETER

    Is there any chance I could purchase a HP optical slot detector from your company and have it sent to the UK? I've searched for this and its the one thing I think I'm going to have the greatest difficulty acquiring at a reasonable cost.

    Thanks again for your help and I look forward to hearing from you.

    Kind regards

  • In reply to Teresa Smith:

    Hi Teresa,

    "Galvanometer" = "Millivoltmeter"......same thing...you do not need to order both.

    The meter you found is a regular panel mount, and looks a bit small.

    What you want is a edge-wise meter - like this old Simpson classic:

     http://compare.ebay.com/like/330755888980?var=lv&ltyp=AllFixedPriceItemTypes&var=sbar

    Search UK Ebay for "edgewise meter" - Ebay forces me back to the US site...so I can't look for you...

    You do not have to use an edgewise meter - you can use a standard panel mount meter with a <1mA movement. A 60mm or larger (the better) meter. Larger meters have the longer needles (which becomes the balance arm) which give more leverage (sensitivity), and more room for the optical sensors...

    Ideally it should be a DC ammeter with a <1mA movement. DC voltmeters can also be used, but you will need to remove the scaling resistors (either external or internal).

    You want a "D'Arsonval" or "Moving Coil" meter movement (coil around a magnet, with a tension return spring, with a fixed pivot point). "Taut-band" meters may not be suitable because they cannot generally be operated at an angle (no bearings) and may not have enough strength.

    This Multicomp SD80/100 looks like a perfect candidate - and it is available new from Farnell for 15 pounds.

     http://uk.farnell.com/multicomp/sd80-0-100ua/meter-81x81mm-0-100ua/dp/4433932

    (I would recommend ordering two - just "in case"...as the movements are very delicate and easy to destroy once they are out of the case.

    The "slot" optical detector is just a LED and a photodiode in one package - nothing fancy or magical about it...you can replace it with separate LED and a photodiode.

    I did not find one at Farnell or Maplin, but Digikey has a similar one (they will ship to UK):

     http://www.digikey.com/product-detail/en/OPB621/365-1665-ND/1636993.

    Here is a nice milligram weight set for $12 - and they ship Int'l:

     http://www.ebay.com/itm/MILLIGRAM-CALIBRATION-WEIGHT-SET-1-TO-500-Mg-/330506905405

    These should get you started. No need to get too fancy. The rest of the parts can be scrounged up anywhere.

    It will take a little mechanical imagination to put it all together.

    Regards,

    Regards,

    Paul Grohe

    TI Comparators (CMPS) Applications Group

  • In reply to Paul Grohe:

    This is extremely helpful - thanks!

    I'm going to buy the Simpson edgewise meter like you suggested as it looks the most similar to what you used. I'm now on the hunt for the basic elements you mentioned on the YouTube video, namely the:

    - analog optical feedback circuit:
    my partner has tried to explain to this to me but I'm no engineer so don't understand, can you shed any light on what components would be suitable to work with the Simpson Edgewise Meter? He's telling me to source and buy everything then he will make it for me.

    - 12bit ADC:
    http://cpc.farnell.com/jsp/search/productdetail.jsp?sku=SC03531

    - programmable gain amplifier:
    http://cpc.farnell.com/jsp/search/productdetail.jsp?sku=SCTLC271CP

    - basic stamp controller:
    having trouble finding a suitable cost effective one - any suggestions?

    - display:
    does this come with the stamp controller or is it better to buy separately?

    This is really quite a challenge for a Lash Artist so my mechanical imagination if fairly limited but I'm determined to make one of these! :)

    Kind regards
    Teresa

  • In reply to Teresa Smith:

    Hi Teresa,

    Note that the Simpson meter is a 10V voltmeter - so there will be a resistor that will need to be removed or bypassed. This should not be a problem.

    The "Programmable" amplifier you selected is not quite correct. That one has an adjustable *speed*, not gain (amplification) - so it would not work.

    What I meant by "programmable" amp is something like the PGA112 or PGA281 - a "differential" input amplifier where you are able to select the amplification steps.

    In the circuit - you will need to be able to measure the *difference* between a "reference" voltage that establishes the "zero" position, and the voltage on the meter coil when the weight is applied. The difference in the reference voltage and the meter voltage is proportional to the weight applied.

    At low weights, this difference will be less than a 0.0001 volt. At full-scale weight - this could be a volt or more - so there is a wide range of gains required (think of a microscope, and how you have to change the lens "powers" as the things get smaller). To get more accuracy at the lower weights - the gain (amplification) must be increased so you can see it (fill the input range of the A/D).

    The amount of change is dependent on the physical/mechanical properties of the meter movement - so you will not know what gain ranges you will need until you test the movement and find out what it's limits are. At some point you can develop a "volts per milligram" number that will allow you to calculate the needed gain.

    I used a Parallax Basic Stamp 2 because I had used it previously in another project and was familiar with it, and I did not have time to learn "real" micro-controller programming and displays. You can use whatever platform your partner is comfortable with.

    The display is the Parallax 2x16 back-lit LCD display - also from Parallax (an "accessory").

    Disclaimer: I designed this when we were National Semi - and we did not have any "micro-controllers" to speak of at the time...So I used what I had in the time allotted... :)

    I would hold off on other purchases until you get the meter, sensor and the weights - as it will require some time to characterize the movement and get it working (the important part...). Once you have the scale movement constructed - everything else will just fall into place and become obvious. The circuitry is the easy part....

    Regards,

    Regards,

    Paul Grohe

    TI Comparators (CMPS) Applications Group

  • In reply to Paul Grohe:

    Hi Paul

    Ok thanks for the clarification. I'll get my partner to read this when he gets home as it'll make more sense to him.

    I'll also hold off on any more purchases like you said and get the basic basic mechanics working first.

    Thanks again for all your help, it would have been impossible for me without your guidance.

    I'll keep you posted on my progress, so you'll be hearing from me again in due course...:)

    Kind regards
    Teresa

  • In reply to Teresa Smith:

    Any chance there is a way to see the schematics as designed for reference?

    What did you use to calibrate the scale to below 100micrograms?

    Thanks,
    Matt 

  • In reply to Matthew Derstine:

    Hmmm... Does not seem my reply made it... I'll try again...

    HI Matthew,

    (Hopefully) attached is the schematic for the movement part of the scale.

    0118.Scale_Schematic.pdf

    There were two pieces, the upper "movement" daughter-board and the "base" board that contained the second diff-amp stages and processor/display.

    The amplifiers I used on the "Base" part are now discontinued, so I do not want to pollute the universe with an obsolete schematic (and to prevent future "where can I find" posts). But that part was fairly straightforward (amps and ADC's)…the important part is the movement amplifier. The actual output would be the difference between the 1V reference voltage and the "Vmeas" output. For best results, connect your DMM between the "Vmeas" output (TP5) and the 1V reference input (TP3).

    Again…the ultimate sensitivity is determined by the meter movement, so you may have to tweak the values of R1 and R5. Basically you want to set the "zero" current to half the meter display rating (i.e.: the meter would be displaying mid-scale). Final 'zero" was set by adjusting the vane on the movement using the meters mechanical adjustment.

    The smallest calibrated weight I had was 1 milligram (basically a little sliver of thin sheet metal).  That set the upper limit.

    To measure below 1mg, you have to rely on physics…

    If you move the weight to half the distance of the fulcrum to the pan, then the resulting measured weight will be half.

    So I marked the shaft at 0.1, 0.25, 0.5 and 0.75 increments.

    I created "weights" out of a strand of hair and a piece of folded tape. The hair was formed into a loop (for hanging) then clamped between the folded tape. The 1mg weight was calibrated, then the "tape weight" was then placed in its place and the edges of the tape trimmed off until it measured what the 1mg weight measured. Get a sharp pair of small embroidery or dissection/surgery scissors…

    Then the "tape weight" was slid down the shaft to the marked 0.5 or 0.1 points, where it then should weigh  ½ or 1/10th what it did at the calibrated "pan" point. From there you can create a "calibration" curve.

    Have fun!

    Regards,

    Regards,

    Paul Grohe

    TI Comparators (CMPS) Applications Group

  • In reply to Paul Grohe:

    Thanks! This is just what I needed. I was unsure about how to bias the phototransistor. Perfect solution.

    Thanks for the info on calibration. Seems easier than the other technique I found which is measure the longest length of fine magnet wire that can be done in the calibrated range, measure and cut to get smaller values.

    Regards,

    Matt

  • In reply to Matthew Derstine:

    Hi Matt,

    Glad to help.

    Here are some old pix of my movement....;^)..

    Here is the original meter, opened up. Notice the black half-moon "disk" vane with the copper area - this was part of the "alarm" setting function. That disk moves with the needle and makes contact with the sliding contacts.

    Here is a pic of the movement mounted - When set on it's side side, the edge of the vane sits in the beam of the sensor and "modulates" the light.

    The entire arm now "balances" on this beam of light.... The power is on, otherwise the needle (arm) would be lowered.

    And here is a close-up of the vane in the pickup "balancing" on the light beam:

    (BTW: The "beam" is infrared...so you cannot directly see it, but bright room light can still interfere with the photodiode)

    Hope this gives you some ideas...

    Regards,

    Regards,

    Paul Grohe

    TI Comparators (CMPS) Applications Group

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