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So, after lurking around in the shadows for years I've finally gotten round to making my first step-by-step instructable.  *yay*

A little background as to how this whole idea came about.

Back in 2009, I needed some bend sensors for a sign language translation glove I was making for fun, and the commercial ones that just came out were over my budget considering I needed at least 10. 

Then I came across plusea's DIY bend sensors on Instructables.
It was what I was looking for but I had one small problem. Well, a few problems actually. (Not with the 'ible of course)
All the different instructables required the use of neoprene, or at least conductive thread and conductive fabric.
I could get the anti static bags locally, but getting the above items would mean the total bill (after shipping and currency exchange rates and tax) would consist of mostly that, and not the cost of the items.

So I decided to see if I could just experiment with the conductive anti static bag(although in all honesty I tried matching it with a whole bunch of other stuff; like carbon paper). It took 2 weeks of playing around during my free time before I finally had a decent build. (Still works to date! )

So for all of you who has a tight budget or like me, can't get easy access to items in the states, this is for you.



Step 1: Materials and Tools

Aside from the anti static bags, you should have the rest lying around or easily make your own wires.

Materials
◆ Anti Static Bags 10x15cm ( I used Vermason Conductive Bags) element14/ farnell order code: 522740 
    ◣  http://sg.element14.com/vermason/bp3eg/bag-conductive-100x150mm/dp/522740?Ntt=522740
◆ Cable Tie (20 - 25cm is great)
◆ Masking Tape (We have them in 3 sizes here. But I found the 2.4cm and 1.1cm to be great. We'll need both)
◆ Jumper Wires (I'm using ones in 20cm length)
     â—£ http://shop.aiscube.com/Cables-And-Connectors/Jumper-Wires-20cm-Pack-Of-20


Tools
◆ Pencil. I would not recommend mechanical pencils as it's too sharp and it might damage the material while marking out the border. (true story)
◆ Pen Knife
◆ Wire Stripper

<p>Hi,I want to know if it still work when using a smaller Anti Static Bags?</p>
<p>Hi, I will need to make six of these for a glove im using to control some servos with an arduino uno. 1. How do I interface these with the arduino 2. Will i need the voltage divider ? (3) How do i make one ?</p>
1) The same way you would with normal ones, except you need to play around with reaistance in circuit.2) highly dubt it, but id yes a bunch of resistors will do the job. )Tutorial there ia for a reason?
<p>Apologies for the noob question ! but i was unsure :) thanks for the help !</p>
<p>That's perfectly normal and nothing to apology for. Just keep on learning :)</p>
I need some help regarding the calibration of the bend sensor. The change in resistance corresponding to each bend is there, but the value doesn't seem to be the same everytime. So eventually it becomes difficult for me to write the code. How do I overcome this problem? I'm using Arduino Uno for the testing.
Hello VigneshK23,<br><br>I'm not too sure if I understand you correctly, but is the change in resistance from resting position to bend position roughly the same?<br>If so, you can just calculate for the change (resting value - bend value) to get the approximate bend position. This should help with the drift in values, and also for the different values of the different sensors.<br><br>Cheers
I'm sorry but I don't get you properly. I'll just elaborate ny problem. <br>I'm doing the sensors for a sign language translator glove. I'm testing it using Arduino uno. I connected the sensor through a voltage divider circuit with a 15k resistor. I observed the ADC output on the serial monitor. For one trial, for a fully stretched finger, I got values from 360-400 . For a later trial, I got values in a different range for the same finger position. So that makes it difficult for me to fix the range of values for each finger position.
*my problem
<p>Hi Vignesh,</p><p>Assuming a fully stretched finger is &quot;resting position&quot;, and when you bend your finger (maybe halfway). Is the difference (resting position value - bend position value) about the same across the different trials? If so, you can just make use of the resistance change (difference in value) and not the actual values, since you're experiencing some sort of drift.</p>
<p>Love this instructable. Its exactly what I'm looking for. One question. Will anti static bags that hard drives come in work? They are blue and semi-transparent and I a bunch of em. </p>
Hi JasonR23,<br><br>Unfortunately not, those are just anti-static bags, and similar to the semi-transparent pink ones, black &amp; white ones, shimmery ones, or any other plasticky anti-static bags which fall under the same category.<br><br>The key thing we're looking for is conductive bags, and not anti-static bags. They're very different things =)<br><br>A good way to test them is to use an ohm-meter on the material.<br>The resistance should vary depending on the distance between the 2 points. <br><br>Cheers<br>tonll<br>
<p>I really appreciate the efforts of Instructor.... Very well explained... Most catchy are the replies given by the Instructor...They are really grt..thanks...</p>
<p>true<br></p>
whr do i will get this conductive bags ? <br>
<p>the comps motherboard comes in em</p>
<p>thanks a lot :)<br>and can I use it instead of a linear rotative potentiometer on a square wave oscilaltor? for controle over frequency?</p>
<p>Hi There! Nice project! Have a question here: If I want to connect 2, 3 or 4 flex sensors in my Arduino, is it necessary one voltage divider for each one? Or just ONE voltage divider is enough for connect all of them? Thanx for sharing this DIY !! Greets from Argentina!!</p>
Hello! Thanks!<br><br>You'll need a voltage divider for each one of them. =)<br>Hope that helps.<br>Greetings from Singapore =)<br><br>Cheers<br>tonll
<p>Hi again! Thanx for your reply! I&acute;ve got another question here.<br>I&acute;m having some trouble here trying to get Velostat sheets. Is there any similar product or replacement material I could use instead of Velostat?<br>It&acute;s getting difficult to me to get Velostat here in my country (Argentina). I&acute;m trying to get some conductive fabric but got the same problem :(<br>Any idea?<br> Thanx a lot for any help you can share with me.</p>
<p>Hmmm.. would getting some off ebay work? </p><p>otherwise, your local distributors of farnell/RS/digikey/mouser or equivalent in your country might work.</p><p>Pretty much guess work. Hope you get it sorted out.</p>
<p>Hey! I can't seem to find any Velostat or Linqstat or black conductive bags (as you have used here) in any hardware store. I live in Europe and can't find an online shop to order some also. Any help on a substitute material that is easy to find or some shop that ships it worldwide? Thanks!</p>
Hello!<br><br>UK Farnell has it. <br>http://uk.farnell.com/vermason/bp3eg/bag-conductive-100x150mm/dp/522740<br><br>You can check to see if your country is listed under &quot;Change Country&quot; - Europe <br>Hope that helps!<br><br>tonll<br>
<p>Do you think that this might work (the bag in the ebay link provided) ? I've found some on ebay, and can be shipped to me. <br><br><a href="http://www.ebay.co.uk/itm/BLACK-CONDUCTIVE-BAG-102X102MM-PK100-006-0002FI-1687802/271241147817?_trksid=p2047675.c100011.m1850&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D24436%26meid%3Da46034c049d34fb4b4c073886a748fae%26pid%3D100011%26prg%3D9173%26rk%3D1%26rkt%3D10%26sd%3D320843661626" rel="nofollow">http://www.ebay.co.uk/itm/BLACK-CONDUCTIVE-BAG-102...</a></p>
<p>It does look similar, and it'll probably work.</p><p>But there's no datasheet, so I'm not sure if you'll get the same results since the resistance could be different.</p><p>Cheers</p>
<p>what are the range of values will u get from this sensor</p>
<p>what are the range of values will u get from this sensor</p>
<p>Hi tonll / Michelle! Quick question here: I have some of the silver-gray, semi-transparent anti-static bags that are also common, do you know if this sensor would work with those too? You specifically say to use the heavy black bags (Velostat, which I'm not as familiar with), so it sounds like it won't work with the silver-gray bags.<br>So, I'd need to use something that looks like the image here:<br><a href="http://sg.element14.com/multicomp/006-0003f/black-conductive-bag-100x150mm/dp/1687804?in_merch=true&MER=MER-L53-L5IB-PD-ALT-TPS" rel="nofollow">http://sg.element14.com/multicomp/006-0003f/black-...</a></p><p>and the bag in the image here wouldn't work?? :<br><a href="http://sg.element14.com/multicomp/mc35830/bag-static-shielding-355-x-254/dp/2135903" rel="nofollow">http://sg.element14.com/multicomp/mc35830/bag-stat...</a></p>
<p>Hello!</p><p>Hmm. I'm not sure if it'd work as I haven't tried it on those anti-static bags.</p><p>2 main important points to note is that the velostat bag is made of a electrically conductive material (carbon), as well as the surface resistance.</p><p>A quick test that can be done to see if the bag you have conducts, is by taking a multimeter and measuring the resistance from one point of the surface of the bag to another.</p><p>Changing the distance of the 2 probes from each other should result in a proportionate change in resistance reading. As with the velostat bag, readings tallied with the datasheet's specs of 100K ohm ++ to values in mega ohms. </p><p>Which in turn, affected the size I chose for the final dimensions used. (due to the resistive readings)</p><p>Although the silver grayish bags have a surface resistive spec, the build of it uses polyester, and the datasheet says nothing about it being one of those conductive polyester films that has carbon black in it. </p><p>I'd suggest trying the above test method.</p><p>Hope that helps!</p><p>Cheers</p>
<p>Thanks for the quick reply! I figured it had to do with the surface resistance, thanks for confirming and sharing the testing idea. I'll try it out and see if it works.</p>
Hi. Just wondering if the resistance value is more linear than logarithmic?
Hi there just for the sake of trial what is the range of values that you get?
Also i have it working, in the way that if i press the surface it goes up the voltage, but only if i press there not if i bend it... what can it be worng?
Hello <br> <br>With the voltage divider, would you beable to show a picture of the circuit from underneath or tell me, because I do not know where to solder together for current to flow through in the right directions. I can't read the schematics well. <br>Thankyou
Do you know some material to replace Velostat?
Hi guys <br>I just wanted to ask, what level ohm or kohm resistors are being used for the voltage divider I have 100ohm resistors would they be sufficient for the voltage divider, I will be using arduino to do this project. <br> <br>Also, I am making a robotic hand which is controlled by the flex sensors connected to a glove, would this type of homemade flex sensor do the job well and be sensitive enough. <br>It is for a competition and will be doing more than just the glove.
Hi,<br><br>Please refer to step 5 for the diagram and values of the resistor for the respective voltage.<br><br>Most arduinos are 5V systems. So you'll probably need 2x 10k Ohm resistors.<br><br>Yes. It's sensitive enough. If you read the introduction, these sensors were originally made for use with a glove for a sign language translation application.<br><br>Hope that helps!<br><br><br>Cheers
Great DIY ...i def want to make these ..... 1 question tho would i need to use the voltage divider circuit you used for an arduino application of these sensors???
Hello!<br>Thanks! =)<br>Yes, you do. Depending on the arduino you're using, please following the resistor values for a 5V or 3.3V arduino version.<br>Cheers
sorry for the newbie question. Just getting started. I'm using arduino. I'd like to try this with it. How do we know which of the wires from the flex sensor goes to VCC and which goes to GND?
Hi, you'll need to connect it to a voltage divider before you can connect it to a microcontroller.<br>Please read through the entire instructable, you'll find helpful schematics on step 5 that states that the sensor is just like a variable resistor, and how you can perform the interfacing.<br><br>Hope that helps!<br>
Hi Tonll, <br>Thanks for your reply. I did read the through the entire instructable and I saw step 5 and the illustration for 5V. As I said I am a newbie so perhaps I'm misunderstanding something (although I've been reading a ton on electronics as well as beginning the MITx class EE). I used the Flex Sensor from Spark Fun and it too needs to be wired through a voltage divider. Your schematic in Step 5 looks like the schematic I used for the wiring of the Spark Fun Flex Sensor. So I thought I knew what I voltage divider was. In the Spark fun Flex sensor there is a lead that goes to VCC and one that goes to GND. My question was which of the leads in your Flex Sensor goes to VCC and which goes to GND ? Maybe it doesn't matter or maybe I'm missing something? <br> <br>Thanks again!! and great instructable
Hi mhussar,<br> <br> It's great that you're picking up electronics and programming. I hope you have fun with the many adventures I'm sure you'll have. =) Makes life all the more interesting.<br> <br> From what you have expressed in your post above, it seems to me (I could be wrong) that perhaps there's been a fundamental misunderstanding of what resistors or maybe just the flex sensors are, and its role in a voltage divider. If I may try to explain as plainly as possible from now on, so hopefully it clears some misunderstandings and make you go AH-HA! or OOOOH! out loud as you're reading.<br> <br> For that, here's some background references for what I'm about to explain.<br> Since you're coming from a previous understanding of the Flex Sensor that Sparkfun carries;<br> &acirc;—†Tutorial for the flex sensor I assume you're referring to:<br> http://www.sparkfun.com/tutorials/270<br> &acirc;—†There's a great link on explaining what voltage dividers are here:<br> http://www.sparkfun.com/tutorials/207<br> <br> &quot;I used the Flex Sensor from Spark Fun and it too needs to be wired through a voltage divider.&quot;<br> Actually, The reference circuit given in the&nbsp; datasheet uses the sensor as a resistor to form part of the voltage divider. Because the flex sensor is just that. A resistor that varies when it bends. The same concept goes for the DIY Bend Sensor.<br> <br> &quot;In the Spark fun Flex sensor there is a lead that goes to VCC and one that&nbsp;goes to GND.&quot;<br> Back to my previous point. It's a resistor. Resistors have no polarity. The flex sensor's (carried by Sparkfun) leads are actually interchangeable. You don't actually connect one to VCC and the other to GND. It's used as R1 of a simple voltage divider circuit. So one goes to VCC, and the other lead to another resistor of a chosen value (pre-calculated) that connects to GND. In which case you then take the point in between the 2 resistors, and connect it to an ADC pin. (Refer to the voltage divider equation at this point)<br> <br> To help visualize and maybe simplify things.. I made an image.<br> I really hope that helps.<br> http://www.instructables.com/files/deriv/FFQ/NG9W/H5TUCAFL/FFQNG9WH5TUCAFL.THUMB.jpg<br> <br> So when you asked this before..<br> &quot;My question was which of the leads in your Flex Sensor goes to VCC and which goes to GND ?&quot;<br> Actually... I answered your question.<br> &quot;the sensor is just like a variable resistor&quot;<br> <br> I really hope at this point, you've understood.<br> If you still don't, please point out which part you don't understand, and we'll try again from there.<br> <br> Cheers.
Oohh and Ahh. <br>Totally get it. Not sure where I picked up that Flex Sensors have polarity. Maybe I mistook the brown bit on the right wire in the Spark Fun Flex Sensor as indicating polarity. However, as I am beginning to understand in general, once one grasps these concepts more fundamentally, mistakes like that should be less likely to happen. I already knew that resistors don't have polarity and also how a POT works as a variable resistor creating a voltage divider. Just didn't get that the Flex sensor was essentially the same thing until you explained it. Thanks so much!!!
Hey! YAY! You got it! Hahahah. That's great!<br>Glad I could help. And yeah.. gain as much experience as possible while learning. You'll find that doing will let you appreciate all the theory even more. It did for me.<br><br>Cheers
Your design would have a limited use-life and the fatigue reading would degrade after a threshold number of bends is reached. Better materials (plastic dip perhaps) to take the place of the tape would increase lifetime use of the sensor. I really like the simple approach you used to address a need. You prove we need not be slaves to commercial suppliers when we really CAN do it our self. I hope to see more instructables authored by you.
Hello. Hmmm. Maybe. I don't exactly have a technical specification and test results that prove that point about the fatigue, but it has done its job for the time frame of at least 8 months that the project lasted. (the occasional taking out and playing with it) <br>I do like your idea of plastic dip. And yes, I agree that better materials will really take this sensor's life time and perhaps performance to the next level. But at that time, I really had to make do with what I had lying around. And this instructable was the result =) <br> <br>Thank you for the motivation. I really hope to be submitting more instructables very soon. <br>
it doesnt matter if the life is low atleast its like 10 times cheaper!!and could ya tell us ur idea(with plastic dip?)

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