EMG muscle sensor: Op-amp models and safety

Discussion in 'The Projects Forum' started by x1222, Aug 15, 2012.

  1. x1222

    Thread Starter Member

    Oct 22, 2011
    I'm planning to use op amps to make a EMG muscle sensor to move my robotic arm. I'm following this site http://www.instructables.com/id/Muscle-EMG-Sensor-for-a-Microcontroller/

    I only know the basics of op amps. In the instructables he uses TL072 and dual low noise op-amp. I only have TLC279 op amps which are single supply op amps. I'm not sure about the difference between them, but would it be a problem? Also he uses an INA106 Precision Fixed-Gain Differential Amplifier. I'm assuming I can just put a TL072 or TLC279 in a differential setup?

    Lastly, reading other EMG posts they used similar op amp circuits with electrodes for sensing the heart. In this case they said not to stick the electrodes on your arm due to safety, but reasons why wasn't specified. I'm assuming the problem is the very tiny chance of a surge of current going up your arm and down to through your heart. Is it really an issue? Would have another metal electrode/brace on my shoulder connected to ground fix prevent this then? Thanks.
  2. praondevou

    AAC Fanatic!

    Jul 9, 2011
    The current that flows through your body depends on the electrode to skin resistance and the voltage applied. If you work with low voltages like 9V I would say it is impossible to receive a shock you could feel (with electrodes attached to your skin). It certainly will not harm you. The situation might be different if you worked with needles because the inner body fluid resistance is much lower. (I posted it in one thread a while ago).

    You will try to measure very low signals , that means you need low-noise components. So you cannot use any opamp. You can try other opamps but they might not give the same results as the one the author used.
  3. t06afre

    AAC Fanatic!

    May 11, 2009
    Will this (doom) device:p but used on real patients as medical device. Or just volunteer people. If it is for real patients the safety requirements are rigorous. But if you and your friends want to safe. The best thing is to use batteries. Say using two 9 volts batteries to make a +/- 9 volt power supply. Will by any means not be able to give hazardous conditions in equipment with skin connected electrodes
  4. wayneh


    Sep 9, 2010
    I have to disagree. I heartily agree that you cannot be at risk of lethal shock or not even a painful shock, unless you take extraordinary actions to seek the pain. Battery to the tongue, that sort of thing.

    But you CAN have a physiological effect and therefore it carries some risk.

    I built a device for a friend that slowly pulses reversing current in the µA range. (Based on the patent literature and a wealth of safety testing, including FDA approval.) Applied with small clips to the ear lobes as the only connection to the skin, these micro-currents induce a profound mood change after a few minutes. Personally, I didn't care for it (preferring ice cold dry gin!) but a large number of folks with chronic pain, anxiety, and other issues find great relief from such a treatment.

    My point is, direct battery connection across the earlobes might induce currents in the mA range and this might be quite dangerous with prolonged exposure. Not lethal, not painful, but maybe not such a good idea.