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Using Arduino => Project Guidance => Topic started by: dany151 on Jan 16, 2013, 06:53 pm

Title: My body gives Electricity when i trying to acquire signal by AD620 inst. amp ?
Post by: dany151 on Jan 16, 2013, 06:53 pm
kindly, im trying to acquire signal with ad620 from my eyes for EOG acquisition system ...when i connect the reference lead to the ground i feel sting
in my (-) electrode

http://electrooculography.wordpress.com/


pls help
Title: Re: My body gives Electricity when i trying to acquire signal by AD620 inst. amp ?
Post by: DVDdoug on Jan 16, 2013, 07:58 pm
What power supply voltage are you using?   Are you running off batteries, or from an AC power supply?   I'm wondering if you have some (potentially dangerous) leakage in your AC power supply!
Title: Re: My body gives Electricity when i trying to acquire signal by AD620 inst. amp ?
Post by: silverxxx on Jan 17, 2013, 06:59 am
this is probably caused by using a switchmode supply somewhere in the device. try using batteries, or connect the ground to earth.
Title: Re: My body gives Electricity when i trying to acquire signal by AD620 inst. amp ?
Post by: oric_dan on Jan 17, 2013, 08:31 am
You have to be EXTREMELY careful when connecting anything electrical to the human body.
Commercial devices have to be very carefully designed so they don't pass very much electrical
current through the body. People who design this sort of equipment have to be highly trained
and licensed too. 9V on wet skin can give you a shock. 120V will kill you.

So, if you're using any kind of AC-powered equipment, and you're not really an experienced
electronics person, what you're doing may be very dangerous. If you insist on doing this,
everything should probably be running off of low-voltage batteries, like 3-4V, and not connected
to your computer either.
Title: Re: My body gives Electricity when i trying to acquire signal by AD620 inst. amp ?
Post by: arduinohabib on Jan 17, 2013, 09:04 am
I'm 13 right now and the first time I was shocked by 220v ac was probaly when I was 5. Since then, I've been shocked quite a few times. Electricity here is 220v.
Title: Re: My body gives Electricity when i trying to acquire signal by AD620 inst. amp ?
Post by: Grumpy_Mike on Jan 17, 2013, 10:08 am

I'm 13 right now and the first time I was shocked by 220v ac was probaly when I was 5. Since then, I've been shocked quite a few times. Electricity here is 220v.

So far you have been lucky. The amount of pain iis dependent on how much current passes through you and where it passes. With electrodes you are minimising the resistance of you and so is much more dangerous than a casual schock.
You must have at lease a 1M resistance in seriese with electrodes.
Title: Re: My body gives Electricity when i trying to acquire signal by AD620 inst. amp ?
Post by: arduinohabib on Jan 17, 2013, 10:53 am
How much is the resistance of a normal person?
Title: Re: My body gives Electricity when i trying to acquire signal by AD620 inst. amp ?
Post by: AWOL on Jan 17, 2013, 11:04 am
Anything from a few hundred ohms to tens of kilo ohms, depending on moisture.
Title: Re: My body gives Electricity when i trying to acquire signal by AD620 inst. amp ?
Post by: arduinohabib on Jan 17, 2013, 01:04 pm
Oh I thought it was about 400k for females and 600k for males.

EDIT
So I guess I can use myself as a pull-down reistor if I run out of resistors!
Title: Re: My body gives Electricity when i trying to acquire signal by AD620 inst. amp ?
Post by: dany151 on Jan 17, 2013, 01:38 pm
thnx for all ... i was using DC power supply ...but now im using 9v batteries  and  isolate myself and my work from electricity.... but i got a sequre wave on the output of AD620 ..... my friend told me that the transistors reched saturation region so change the input voltage to 3v ....but i see most of researchs used 12v as input ....any one have used AD260 before can help me ?? i will make a new topic for that ...thnx again
Title: Re: My body gives Electricity when i trying to acquire signal by AD620 inst. amp ?
Post by: Grumpy_Mike on Jan 17, 2013, 05:46 pm
Why do you say in the title that your body gives electricity? It OS not giving it it is taking it.
If you need help you need to post a schematic of your circuit.
Do not start another thread.
Title: Re: My body gives Electricity when i trying to acquire signal by AD620 inst. amp ?
Post by: CephasAntipodes on Jan 18, 2013, 09:19 am
The square wave you are seeing may be due to 50Hz mains pickup. You're in England (or Ireland/Scotland/Wales), I assume?

You can try a couple of things. First, check the frequency of the square wave. If it's 50 or 60Hz, it's mains interference. If you're running the circuit from batteries, you don't need high resistance in your electrodes. Try reducing the resistance to about 10k, that should significantly reduce the mains pickup.

If the square wave signal is in the frequency range you're interested in (200Hz...20kHz), then add a resistor of about 47k between each lead and ground. This will act as a voltage divider, and might be an easier way to reduce the signal voltage.

You should be seeing signals of only a few millivolts - maybe 50mV maximum. If you're seeing voltages in the volt range (1V or higher), then you're an antenna, and you're picking up voltage from somewhere else! Also, you'll find that any televisions in your area will tend to induce voltages in you. Turn off the telly, or better yet, go into the back yard/garage and try there if that's possible.

The only other thing I can think of is if you're living under power lines. They will cause you all sorts of problems, at all sorts of frequencies.

As someone suggested, maybe if you post a schematic (circuit), it will help to pinpoint any unusual problems or potential danger points.

Given that you connect your probes to each temple and one in the middle, I'm surprised you didn't turn into Frankenstein! Did smoke come out of your ears? :)

Let us know how you got on, it sounds an interesting project!
Title: Re: My body gives Electricity when i trying to acquire signal by AD620 inst. amp ?
Post by: takumikm on Sep 23, 2014, 09:09 pm
yes that's completely normal, if you are making your own power supply, there are 2 ways to solve this:
1) use 9v batteries instead of power supply, also since it's DC current you don't have to use notch filter to remove the noise from the AC current.
2) you can use NDTD4815C and ISO124P to isolate grounds and references and have medical grade safety.