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Thread: DIY FSR Feet for the HR-OS1

  1. Re: DIY FSR Feet for the HR-OS1

    Quote Originally Posted by KurtEck View Post
    Price, where did you get such a great deal?
    Got them on eBay (in UK): http://www.ebay.co.uk/itm/161805079939

    Frankly, I just got them at the weekend and I haven't yet tested them properly to make sure everything is ok. But I don't think there are any problems.

    Alex.
    Last edited by sonel; 11-18-2015 at 09:15 AM.

  2. #12

    Re: DIY FSR Feet for the HR-OS1

    Thanks,

    Yes looks like there are a bunch of clones made in China of the Arduino Pro mini as well as some with the Atmega32u4 for quite cheap
    Maybe have to try some.

  3. Re: DIY FSR Feet for the HR-OS1

    After reading your thread I started looking at the Edison MCU. It shares memory with the onboard Atom I think you could use this to read the FSR's in the feet and then you would not even need the mini's. You would need to run four wires down each leg. {-edit-} I have not worked with FSR's before, but I read that they are not very precise and the manufacturing tolerances are pretty wide. I think it is not important to know how much the robot weighs, but where the center of pressure is. You can do this as follows. Connect one lead of the FR (front right) and BL sensor in together in series and one lead of the FL and BR sensors together in series forming an X (axis with 45 deg offset). Wire the remaining leads of the FR and FL sensors together and connect to 5V excitation (first wire up the leg). Connect the remaining leads of the BR and BL sensors to together and connect to ground (second wire up the leg). Connect the center connection point of each axis to analog ADC inputs on the MCU (other two wires up the leg). With even pressure on the sensors, calibrate electronically for foot center of pressure.

    No pressure on foot - both ADC inputs high-z (floating - may need a pull up/down at analog ADC input).
    Even pressure on foot - both analog ADC inputs near 2.5V
    Front pressure on foot - both ADC's between 2.5V and 5V
    Rear pressure on foot - both ADC's between 0V and 2.5V
    Left pressure on foot - one ADC low (0V-2.5V), other ADC high (2.5V-5V)
    Right pressure on foot - one ADC high (2.5V-5V), one ADC low (0V-2.5V)

    I think the FSR's go open when there is no pressure, this may cause an issue. I would need to think through it more. Really what you end up with is an analog X-Y axis that is rotated by 45 degrees with respect to the foot. Care would need to be taken with the 5V excitation to ensure that it could drive the low impedance load (200 ohms? - 2S2P).

    I would be curious to know if anyone actually tries this. If not, I might try to get some FSR's sent to the house and give it a go.
    Last edited by Mike.; 11-18-2015 at 01:50 PM.

  4. #14

    Re: DIY FSR Feet for the HR-OS1

    Hi Mike,

    I don't believe the Edison comes with any Analog to digital converters. The Arduino version of the board has some built in. Also it has been awhile since I tried out the Edison with the Atom, but at that time the IO performance of the Atom was not impressive... Hopefully soon they will have a new release.

    Note: you could try to attach an AtoD converter, such as: https://www.sparkfun.com/products/13327 onto the Edison, but each of these only gives you I believe 4 Analog inputs, so you would need to mount two of these. To use these you would probably need to run probably at least six wires down each leg (maybe 5) (4 inputs, +5v and ground). Note you can probably do similar things for the Raspberry PI, by hooking up an external AtoD converter, as described in: https://learn.adafruit.com/reading-a...ry-pi/overview. Currently I am using an Odroid C1 on mine, which I believe has 2 AtoD pins on it.

    A nice thing about r3n33s approach is you don't need to run any wires down to the feet. You simply plug ones of these boards into the AX chain at the feet and read the values in over the AX buss.

    Soon, I may build up another simple circuit like I did for the LEDs to make it easier to hook up.

    Will be fun!

  5. Re: DIY FSR Feet for the HR-OS1

    Hmm, I had looked up Intel's page over lunch, it looks like they accidentally swapped the photo's and I just read the specs based upon the photo:
    http://www.intel.com/content/www/us/...ison.html#kits

    You are right, no ADC's on the mini-breakout. I didn't realize r3n33 was going to use the existing bus, pretty neat!

  6. #16

    Re: DIY FSR Feet for the HR-OS1

    The trinkets are fun, small arduino's in a sense. Any advice on you FSR feet, I think I have all the parts together and printed up, I'd love
    to incorporate these into my robot or help if I can. I might need a little better hook up advise/pictures but Woot!

  7. #17

    Re: DIY FSR Feet for the HR-OS1

    I don't have the parts yet, but plan to add them to mine as well.

    I have been doing a little hacking of another HAT for an Trinket Pro to handle this. Currently the 3d model looks sort of like:
    Click image for larger version. 

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    The part toward the bottom, which I don't have 3d model for yet, is for an 6 pin inline bused resistor network, which I have setup for 10K going to ground. I also currently have it setup to be able to have multiple AX connectors, but may not be necessary as this is at the end of the chain...

    So may play with the ability to add a neopixel for the fun of it instead . Also I have in it an extra voltage divider connected up to AX buss so can have it respond to current voltage (optional). Diode shown on top is actually probably not needed (actually by default I have it shorted out beneath it)...

    My assumption for hooking up the FSRs is that each one goes in as a voltage divider, with +5v going to one pin of the FSR, the Other wire connects up to an Analog pin on the processor as well to a 10K resistor where the other pin of the resistor connects to ground.

    Kurt

  8. #18

    Re: DIY FSR Feet for the HR-OS1

    Got my FSR's today. Going to start the foot assembly, them are 10k resistors right?Click image for larger version. 

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    Last edited by LloydF; 11-24-2015 at 06:07 PM.

  9. #19
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    Re: DIY FSR Feet for the HR-OS1

    Quote Originally Posted by LloydF View Post
    Got my FSR's today. Going to start the foot assembly, them are 10k resistors right?Click image for larger version. 

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    Looking great. Yes I do believe they were 10k but I'll have to double check. I suppose we'll have to work on getting you the FSR firmware sooner than later.
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  10. #20

    Re: DIY FSR Feet for the HR-OS1

    Yes, probably need to finish debugging the firmware. Was waiting until I had feet parts to work on it, hopefully soon.

    Also I may play with a larger version of the board I showed above that hopefully could position inside the foot and have it setup where you could then probably solder the FSRs directly to the board. or optionally some form of connectors...

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