emg signal + robot hand

Forum 2005-2010 (read only) Hardware Interfacing
1

Hi all, for a school project i am making a robotic hand controlled by EMG signals. The signal from electrodes on the forearm are being amplified and put through analog filters to create a decent signal. My question is what should the final signal look like once it is input into the Arduino? For example to make full use of the A/D converter should it be as close to 0-5V as possible? What happens if the signal goes out of bounds (below 0 or above 5V)? I realize that this question may be somewhat vague, but I'm really just a beginner at using microcontrollers, but I'm learning... We have a signal from the electrodes, but are afraid to give it to the Arduino for fear of wrecking something.

If someone has any advice/criticism please comment.

Thanks.
Karl

2

what should the final signal look like once it is input into the Arduino? For example to make full use of the A/D converter should it be as close to 0-5V as possible?

Yes it should

What happens if the signal goes out of bounds

You end up damaging the Arduino.

If there is a chance of this then use some protection and catcher diodes. See:- http://www.thebox.myzen.co.uk/Tutorial/Protection.html

Best of luck it is not an easy project.

3

It depends upon your amplification/conditioning circuit. How much current can it source? how sensitive is it to current loading? how much precision do you really need in the A/D inputs?

Protection diodes can add a small amount of leakage current which can disturb the measurement output, depending on the output impedance of your circuitry.

4

depending on the output impedance of your circuitry.

By the time you get up from a muscle signal to 5V the impedance isn't going to be that high is it?

5

If you're constructing the filter/amp circuit yourself, why not do so such that the output is restricted to 0-5V?

6

hi, thanks for your replies.

i have the circuit supplying the arduino with an input signal. so far we have basic motor control like this:

  1. flex muscle -> move servo forward
  2. stop flex -> stop servo
  3. flex again -> move servo backward

this is really basic, as it simply reads in the input and when it goes high, moves the motor in the direction opposite to the last movement.

we want to beef things up a bit and get a little more complicated. is it a matter of just trying to accomplish this in the arduino ide, or can we utilize serial data output for matlab processing for example.

i guess we have to come up with some sort of pattern recognition. is this even possible?

i'm really at a loss in terms of how to improve this, any guidance would be much appreciated.

7

Am also working on a low cost bionic hand using arduino. Currently am nt using EMG signals but yes it needs a pattern recogniser. There are a few ICs available in the market. Whts the m,aterial of the electrode u r using and where did you buy it from.