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July 6, 2011
about 2 years ago
The 2Hz cutoff is the frequency for the integration circuit. The circuit layout is similar to a LPF but since the signal has been rectified at that point, it acts as an integrator. http://www.electronics-tutorials.ws/opamp/opamp_6.html
about 2 years ago
Customers have used the MyoWare to measure vocal cord activation. You might want to double check your setup. Feel free to email us at email@example.com if you need help troubleshooting.
The reference electrode can be attached areas other than a bony area. It simply needs to be attached to an area that is adjacent to the muscle you are trying to measure. The function of this electrode is to align the sensor’s ground state with the ground state of the user’s body. Yes, a bony area is ideal because it does not produce electrical signals but it is by no means strictly required. For example, the sensor will work perfectly fine for the bicep if you place it along the inside of the user’s arm between the bicep and tricep.
Most of the filtering comes from the high CMRR of the AD8236 which will remove most noise artifacts common to both input electrodes such as the dreaded 50/60Hz electrical “hum”. Other than that there is a high pass filter that is used to remove DC offsets that can be present due to electrode polarization and skin dielectric characteristics. This HPF has a cutoff frequency of 0.33Hz. The EMG envelope output (SIG) has an integration circuit that has a cutoff frequency of 2Hz. (note: the Raw EMG output (RAW) does not go through this portion of the circuitry.)
You can use other batteries besides two 9Vs. That is just a quick and simple example to help people not familiar with dual supply powered sensors. Unfortunately, you cannot power the V3 with a single supply source like a microcontroller. You need a positive voltage and a negative voltage. Keep in mind that a negative voltage is not the same as ground.
That being said, the new MyoWare sensor (which will be soon available on Sparkfun) only requires a single supply power source and can be powered with a microcontroller directly. You can check it out here: https://www.kickstarter.com/projects/312488939/myowaretm-harness-the-power-of-your-muscle-signals
about 3 years ago
It’s an analog sensor so sampling rate doesn’t really apply. It would depend on the ADC/microcontroller/DAQ that you use to measure it.
The Arduino code is meant to be run along side the Processing code. It outputs all six pins so you can connect up to 6 sensors and view their output graphically via Processing.
The biomedical pads are probably too big for measuring eye muscles but the sensor should be able to pick them up if appropriate pads are used.
Are you driving the servomotor directly with the sensor? Usually this is done with a servo driver or microcontroller. If using a servo driver or microcontroller, you’d simply need to map the input values to higher values before sending it to the servo. You could also alternatively increase the sensor gain via the potentiometer marked as Gain in the middle of the board.
This is actually the same sensor board as before. The difference is that the sensor board was packaged as a kit but is now sold separately.
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