Comments: MyoWare Muscle Sensor Kit

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  • ——————– Tech Support Tips/Troubleshooting/Common Issues ——————–

    Tech Tips on Soldering to the MyoWare & Shields

    It’s briefly stated in the tutorial here for installing the headers to the boards => [ https://learn.sparkfun.com/tutorials/myoware-muscle-sensor-kit/putting-it-all-together ]. If you do not know how to solder pins to plated through holes, I recommend looking at our tutorial about how to solder => [ https://learn.sparkfun.com/tutorials/how-to-solder-populating ] the header pins to any of the MyoWare boards. I have provided some detailed instructions on soldering the headers to the boards below:

    1.) Set Up w/ Breadboard

    This step is optional but I placed some male header pins on a breadboard to help solder the pins to the MyoWare and shields. Luckily, the location of the MyoWare’s header pins matched the breadboard’s spacing. I was able to put the headers on row 1 and 20.

    Set Up With Breadboard

    Warning: Make sure that the boards are not powered when connecting the shield on the breadboard. Each breadboard’s is connected together and it will create a short between the “+” and “-” pin. The MyoWare LED Shield has a LiPo battery attached and there will be a short. Try soldering the MyoWare or another shield first on the breadboard. Then remove the MyoWare or shield from the breadboard to assist in soldering the header pins on the MyoWare LED Shield.

    2.) Load Female Header Pins

    For the shields, I decided to use the 1×3 female header pins. The image shows you how to load the female header pins to a male header pin so that it makes it easier to solder the headers. You would need to check the alignment to make sure that the header pins are flush with the shield:

    Loading Header Pins

    You could also use a soldered board to hold the female header pins:

    alt text

    3.) Choosing a Side

    We do not populate header pins on the PCBs. There are many ways to connect to the boards depending on personal preference, which is why we leave this up to the customer. You can choose to solder the header pins on the top:

    Choosing Top of the Cable Shield

    or the bottom:

    Choosing Bottom of the Cable Shield

    For our known good boards, I decided to solder the female header pins from the bottom in order to stack the boards together.

    4.) Solder

    After choosing the side, you will solder the header pins against the board. Make sure that you have sufficient contact between the tip, pin, and the plated through hole of the board so that the there is sufficient heat being transferred to the joint. The image below shows the soldering iron against the the pins. Try soldering to one pin and checking the alignment before soldering the all the pins:

    Soldering

    Warning: Remember the warning in step 1? Well since my prototype LED shield did not have a battery attached, it was fine to use it to hold the pins in place to solder. I removed the battery when soldering header pins with the MyoWare Muscle Sensor. However, the current stock of MyoWare LED shields have a LiPo battery attached and you may damage the sensor. You would be better off soldering the board with installed headers on the Proto Shield [ https://www.sparkfun.com/products/13709 ] to hold the pins in place.

    5.) Cleaning

    Assuming that you are using water soluble flux, you should clean the boards to remove any excess flux on at the solder joint. This prevents oxidation and dendrites (temporary shorts) that can form between the pins. You can use some de-ionized water, toothbrush, and a paper towel. You could also use compressed air, to remove any excess flux residue or water that is on the board. I recommend being careful about cleaning the MyoWare LED Shield. Certain components (like the LED bar graph display, batteries, etc.) are sensitive to water so you should be careful about getting these components wet. You can damage a component if water gets trapped in them and you power the board. For more information, try checking out this section of the tutorial on PCB Washing [ https://learn.sparkfun.com/tutorials/electronics-assembly/the-steps ]. Below shows an image of the solder joints cleaned:

    Cleaned Boards

    6.) Stack the Shields

    Prepare the boards to be stacked and make sure that the silkscreen is aligned. Try marking it with a sharpie or acrylic paint to indicate the polarity:

    Prepare the Boards

    You can stack the shields in any order as long as the silkscreens for each PCB match.

    • MyoWare Reading at Max or Not Responding to a Muscle Group?

      Adjusting Gain w/ Potentiometer

      The potentiometer adjusts the gain as stated on page 7 of the user manual – https://cdn.sparkfun.com/assets/learn_tutorials/4/9/1/MyoWareDatasheet.pdf :

      "...Using a a Phillips screwdriver, turn the potentiometer counterclockwise to increase the output gain; turn the potentiometer clockwise to reduce the gain."
      

      If the gain is too high, the MyoWare might not show a significant change in the “SIG” output when a muscle flexes. As a result, the high output would cause the SIG LED to stay ON or all LED bars on the MyoWare LED Shield to turn ON. Try turning the gain down with a precision screw driver. The gain does not affect the “RAW” output signal.

      Floating Reference or Electrode Pins

      If the black reference electrode cable is not fully connected to your body, this can leave the sensor floating and cause the sensor to constantly output a high sensor value. Make sure to follow the note on page 7 for the Ref pin:

      "Connect this to the reference electrode. The reference electrode should be placed on a separate section of the body, such as the bony portion of the elbow or a nonadjacent muscle."
      

      Incorrect Placement of Sensor on Muscle Group

      Make sure that you placed the biomedical sensor pads to the muscle group correctly. The MyoWare’s embedded electrode connectors are great for small muscle groups if placed on your bicep [ pg 4 and 5 - https://cdn.sparkfun.com/assets/learn_tutorials/4/9/1/MyoWareDatasheet.pdf ]. Below are some images of the MyoWare and LED Bar Graph when my bicep is relaxed:

      Bicep Relaxed

      partially flexed:

      Bicep Partially Flexed

      flexed:

      Bicep Flexed

      However, if you place the MyoWare Muscle Sensor on a larger muscle group incorrectly, it will not read or respond to the muscle group. This might be due to the the mid muscle electrode pin not being placed in the middle of the muscle group. I had problems using the embedded electrode connectors when placing it on a certain part of my right forearm (I believe that I placed it on my “flexor digitorum”). If you look close at the images when my bicep was flexed, there were sensor pads also near my elbow. I was not able to read the muscle group when the sensor pads were placed at that location.

      For certain muscle groups, you might need the MyoWare Cable Shield [ https://www.sparkfun.com/products/13687 and Sensor Cable - Electrode Pads (3 connector) [ https://www.sparkfun.com/products/12970 ] for bigger muscle groups as stated briefly on page 7 of the user manual. For my forearm, I was able to measure it when increasing the distance between the sensor pads using the sensor cable:

      Forearm w/ Sensor Cable

      Loose Myoware Board

      If the MyoWare is loose and not secured, the sensor will amplify the movements when the sensor pads are stretched. According to Brian (the designer of the MyoWare muscle sensor), this is a motion artifact and it is not a genuine signal from the muscle group. The SIG led on the MyoWare and the LED Bar Graph might be partially or fully on. Try securing the MyoWare with some fabric or tape when attached to your body. Also, make sure to adjust the gain to calibrate the sensor. Below are some images showing the

      Slightly Streteched

      Fully Streteched

      Laptop Battery

      If you are connecting an Arduino and debugging with the Serial library, it is suggested to have a USB isolation circuit with the MyoWare to prevent noise in the inputs and the possibility of shock when connected to a power grid (i.e. a computer power supply connected to a wall outlet). If you do not have a USB isolation circuit, try using a laptop in battery mode and make sure that you are not connecting the laptop to a wall outlet.

      Additional Tutorials: Making Custom Adapters w/ E-Textiles


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