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i have to build a kind of dress that can unserstand the blend angles of neck, shoulder, elbow, wrist. i thought the best is to use arduino lillypad and some flex sensors.

i've saw this: http://sensorwiki.org/doku.php/sensors/flexion

but i'm still confused on what kind of sensors could fit best in my project.

for example the sensor in the neck sould be a little more accurate that the one in the shoulder and i don't know if i need a different sensor or i can use different offset via software. then i heard that some flex sensors are going to get broken if they are misuring more than 90° (but.. is it true?) and in my project elbow is blended kind of everytime more than 90°.

can someone give me some advice?

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  • \$\begingroup\$ What accuarcy do you need? \$\endgroup\$ – suha Jun 17 '12 at 23:41
  • \$\begingroup\$ i don't know exactly how to misure it: i need a value between 0 and 256 when the muscle is completly blended.. for sure i don't need a hight accuracy like medical robotics or similar \$\endgroup\$ – nkint Jun 18 '12 at 8:44
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Your best bet is the conductive ink kind of sensor.

Flex sensor

These are a little bit pricey but easy to get hold of. Sparkfun have them for $13.

They're pretty easy to use as they act just like a variable resistor, whose resistance changes as you bend it. You can make them into an analogue sensor by adding a fixed resistor. The impedance buffer (an op-amp) is optional, but will result in much better sensor readings, especially as you intend to use fairly long wires to connect the sensor to the Arduino.

Flex sensor circuit

The datasheet for the sensor (which you should read) contains lots more suggestions for circuits.

You can stitch a little pocket into clothing and insert the flex sensor. Use them in the fingers of a glove:

Flex sensor in glove finger

Or in a whole dress:

Flex sensor dress


Added

Accuracy: Flex sensors aren't super accurate sensors. They give you a reasonable sense of an amount of bend, but aren't great for precision applications, E.G. robotic teleoperation. I don't know how much accuracy you need for the neck, so it's very hard for me to say whether it's good enough for you. If you want a more accurate sensor, you'll need to specify exactly how accurate.

Robustness: What will kill the sensor is not the angle of the bend, but the minimum bend radius.

Minimum bend radius

The datasheet for the ones at Sparkfun didn't mention a minimum bend radius, but these ones specify 5mm. I.E. you can bend one around a 10mm diameter tube, and they'll be fine. So I would imagine that going round the outside of an elbow would be OK, but the inside would probably pinch the sensor and break it.

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  • \$\begingroup\$ thanks for fast replay! i've edited a little bit the question \$\endgroup\$ – nkint Jun 17 '12 at 22:20
  • \$\begingroup\$ @nkint - OK, I'll add some more about this. \$\endgroup\$ – Rocketmagnet Jun 17 '12 at 22:26
  • \$\begingroup\$ ok perfect thanks. last thing: what length? i've seen there are from 1" to 5".. from the length it depends the accuracy, right? more length, more sensibility? \$\endgroup\$ – nkint Jun 18 '12 at 7:58
  • \$\begingroup\$ @nkint - I don't think that the accuracy is affected much by the length. Use whatever length is appropriate for the job. Try it out with a piece of paper cut to length. For the elbow, you'll probably need a long one to make sure you're covering the whole outside of the joint. \$\endgroup\$ – Rocketmagnet Jun 18 '12 at 9:03

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