my experiments and work

The Local Tea Party: Don't mess with the single people

Mon, 18 Jul 2011 16:14:58 +0530

The Local Tea Party: Don't mess with the single people:

All you publicly married and secretly register-marriaged people, leave the single guys alone man. Arey one single guy how many people will make fun yaar?

Have you ever been single in your life? Life is hell only. Especially when that single guy is having married friends or friends in…

aruna bolisetty asked: nothing idiot.. she didn't ask anything did she?

Sun, 17 Jul 2011 15:55:26 +0530

she left a message :)

I like the theme! Not that I understand anything on the blog, happy to see you on tumblr :P

Sun, 17 Jul 2011 15:51:09 +0530

Happy to be here! :) i’m opening a personal blog too. how come most of the stuff i see here is photoblogged?

HOWTO: Designing and building a Bioamplifier & Acquisition System : Instrumentation Amplifier & DRL

Sun, 17 Jul 2011 13:59:15 +0530

In this second post i will talking about the design and the configuration of the instrumentation amplifier.

A basic instrumentation amplifier is here : http://www.national.com/ms/LB/LB-1.pdf

National, being one of the earlier semiconductor companies to work in analog have put it well in that application note.

A Biological Signals have a few qualities (mostly irritating), that make them difficult to be picked up and amplified. In biological signals, a signal amplitude of anything around 100uV is considered aking to striking gold. Normally we deal with signals that are in the range of few tens of microvolts. and the current that is noticed is generally in nA. The second most important feature is the observed frequency of the signals, they tend to be within 100hz.

At Such low values of voltage and current, a simple set up which is supposed to pick up these signals at high gain, will instead pick up the 50Hz power signal that is radiated by wires carrying electricity that powers your lab or work place (in non shielded rooms), And when connected to your body, your body will act as a antenna for the radiated power signals and then this becomes a part of the input given to the amplifier.

Generally a good quality instrumentation amplifier can handle the 50Hz noise because of inherent ability of the amplifier to reject the common mode voltage while dealing with everyday signals. However, at these low voltages and because the “ground” of the two objects in question. i.e. the patient and the object are different, most medical devices opt for “Active Cancellation”, this technique is referred to as a using a DRL circuit (Driven Right Leg) , the DRL circuit measures the common-mode volatage and sends back a phase shifted signal which cancels the incoming 50hz signal, thus providing a signal clear of any powerline interference.

Now, Let us Look at the design for Channel 1.

The Datasheets one would need are for the:

AD8221 and OP07

The Reference Schematic is:

I’ll be referring to components by the labels in the schematic.

The Front End of the channel first has,

Two resistors and capacitors to make sure that there is no short between the device and the electrode, this was you can ensure that you might not inadvertently electrocute your subject, this is just basic protection better isolation devices using optically coupled isolators are usually used in approved medical instruments.

The diodes are there to prevent any excess voltage from affecting the instrumentation amplifier, since eeg’s have a range of hundreds of uV, this suits us fine.

The ping out for AD8221 Looks like:

The connections are self explanatory.

The DRL circuit is built using the LM358, the LM358 takes the common mode voltage input from the circuit and uses that to generate a signal that will actively cancel the 50Hz noise.

The OP-07 filters the signal, gets the DC offset generated and that is used as reference voltage (Vref) to cancel any baseline drifting and wandering.

This Concludes Part I of the Series. The next post will be on the Filtering process, the gain stage and how to use an analog multiplexer.

HOWTO: Designing and building a Bioamplifier & Acquisition System : Introduction

Wed, 13 Jul 2011 21:34:00 +0530

Okay,

My First Series of Posts is going to be on an EEG Amplifier i worked on during the early months of my M.S. (by Research) at VIT.

This work was heavily influenced by the design on:

http://openeeg.sourceforge.net

However, i’ve used inexpensive amplifiers in the gain stage and few modifications on how we handle the signals. Also, i’ve used an additional digital board to provide USB functionality to the system so that i can get higher sampling rates, even when i have 64 channels.

Lets Start with One Channel.

This is the schematic for one channel.

Now,

The channel provides the complete amplification and signal conditioning that is required to get a good quality signal.

(Click on the image to see a full sized image)

Each Individual Channel Can be split into three Separate Modules.

1) The Instrumentation Amplifier.

2) Driven Right Leg

3) Baseline DC removal

4) Sallen-Key Filter

5) Gain Stage

In the coming post’s i’ll be talking about each of these stages in detail.

Long Overdue.

Wed, 13 Jul 2011 20:15:13 +0530

So,

It has been a busy few months. Running around for my university work and getting my admission details worked out, the documentation etc etc has taken quite a toll. So all the information i’ve been meaning to put up has kind of taken a back seat.

I seem to have a little time before i pack up and leave for the US, so i’ll put up whatever material i have worked on (and i can find).

I’ll just cover a few basic things i’ve worked on in the beginning and then move on to some slightly more complicated things.

Teja

Hello Universe

Wed, 17 Nov 2010 13:47:06 +0530

Hello world is a bit cliched no?

Okay, I’ve Given on personal blogging. But i realize there has to some record of the immensely awesomely cool things i get involved in. From networks to predict your brain waves to random things like metals that can pull 11748 times their weight when they are heated.

Also, i’ve been asked to document everything i do. and there is NO way in <insert eternal place of oppression> that i’m going to be sitting around doing reports.

So expect photographs, simulations and probably a *little* sleep deprived behaviour.

This might involve violence against computers. This blog is PG rated for profanity against machines and dolts.

Photo

Wed, 17 Nov 2010 13:24:34 +0530