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About Muscle signal sensor EMG Sensor for Arduino

nwianiwa

New Member
Please help me with the sensors on this site.

It is a sensor that uses two 9V batteries.
Is there a problem if I use these two batteries as two AC adapters?
Will using two AC adapters break the EMG circuit board?
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Please help me with the sensors on this site.

It is a sensor that uses two 9V batteries.
Is there a problem if I use these two batteries as two AC adapters?
Will using two AC adapters break the EMG circuit board?

Use batteries, you DO NOT strap wires across your heart or other body parts using mains power!! - that was often used in the USA for executing prisoners.

Notice ECG machines etc. in hospitals are battery powered.
 

Pommie

Well-Known Member
Most Helpful Member
Many years ago (sometime in the 80s) a friend (Hi Dave) had designed a portable ECG machine that was battery powered and much cheaper than anything available at the time. Due to the regulations he had to use the same connector for the charger as was used by the pads so they could not both be connected at the same time. Mains and medical devices don't mix.

To the OP, it probably won't work anyway as the two negative rails might be connected via the earth connection but don't try it anyway.

Mike.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
I've had two 12 wire ECG's this year, I still haven't managed to work out where they stick that many wires? :D

I was also covered in terminals a year or so earlier - the ambulance crew did an ECG, and left all the terminals on me. Then when I got to A&E the staff there fitted another set of terminals, then when I was moved to a ward they fitted yet a third set of terminals. Why not just use the existing terminals?, or at least remove the ones you're not using.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
To the OP, it probably won't work anyway as the two negative rails might be connected via the earth connection but don't try it anyway.
Not only safety - skin resistance is quite high, and the body is acting as an antenna.

The reference electrode simply cannot hold the body potential at exact ground voltage, so any signal readings are likely to be swamped by noise and hum.

With a completely isolated or floating (no other connections) type device, the input amplifier either follows or references to the instantaneous voltage on the body, so you don't get the noise and hum interference.
 

danadak

Active Member
Not only safety - skin resistance is quite high, and the body is acting as an antenna.

The reference electrode simply cannot hold the body potential at exact ground voltage, so any signal readings are likely to be swamped by noise and hum.

With a completely isolated or floating (no other connections) type device, the input amplifier either follows or references to the instantaneous voltage on the body, so you don't get the noise and hum interference.

Don't most solutions use a differential front end to reject common mode ?


Regards, Dana.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
Don't most solutions use a differential front end to reject common mode ?
As far as I am aware, the front end (if not the entire machine) is also floating/isolated so it mostly tracks the stray pickup on the body, to minimise the common mode offsets between the reference and signal inputs.

For an amp to accept signals beyond its supply, it means an attenuator at the input, then needing higher gain to compensate. The common mode balance and drift etc. all become more problematic, the larger the common mode range that must be accepted.
 

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