biopotential amplifier - help needed

Hero999 · Dec 23, 2007

Tell me where it says that?
https://en.wikipedia.org/wiki/India

Nigel Goodwin · Dec 23, 2007

Doesn't matter what Wikipedia says really, there are plenty of problems in India, not the least of which is the primative caste system - and like Audioguru said it has appalling poverty, yet at the same time some of the richest people in the world.

It's a big country, and has lots of problems - many from religion like other countries - but also has beautiful scenary and a great many wonderful people.

It probably didn't help being invaded by war mongering westerners?

audioguru · Dec 23, 2007

Hero999 said:
Tell me where it says that?

Look in Google for Uncivilized Countries and India is listed.
Many people interchange the terms "uncivilized" with "the 3rd world".
Anther term used for a different culture is "barbaric".

littletransistor · Dec 23, 2007

audioguru said:
Look in Google for Uncivilized Countries and India is listed.
Many people interchange the terms "uncivilized" with "the 3rd world".
Anther term used for a different culture is "barbaric".

Oh man, this sounds pretty harsh. Then how about Malaysia, which is a 3rd world country too?

hello people...

We are working on a project to control certain home appliances such as a tv using eye movements. The first step of this project involves the extraction of signals caused by the human body due to eye movements.

since these signals are extremely small, (250 to 1000uV) we had to amplify them. We designed an instrumentation amplifier of gain around 1000 using LM741 op-amps. However still we couldn observe the signals on the CRO in our lab. all that we could see was noise.

We tried to purchase instrumentation amplifier such as AD620 and Ad622. Unfortunately they are not available to us.

What possibly could have gone wrong? and pls offer suggestions on how our task can be accomplished.

Okay - first thing first. Try to start this simple. Get a uA741 or any simple opamp, then do a simple negative feedback configuration on a breadboard and connect the electrodes to the body. If you can see some outputs here (especially ECG waves - the QRS complexes can be seen, but with noise pollution) then it is okay. Then, after that, build two buffers and one differential amps together.

If you want to simplify the project, an instrumentation amplifier really helps.

Hero999 · Dec 24, 2007

You obviously haven't read the rest of the thread, he's altready tried the 741 and had problems with it because it's a poor quality old op-amp.

littletransistor · Dec 24, 2007

Hero999 said:
You obviously haven't read the rest of the thread, he's altready tried the 741 and had problems with it because it's a poor quality old op-amp.

Hmm... yeah, he did have problems having the 741.

Well, I suggest building up the circuit one-by-one if one is building instrumentation amplifiers from 3 op-amps.

I did start with one op-amp first, then the differential, then put them all up with the buffers and the differential.

audioguru · Dec 24, 2007

The opamps in an instrumentation amp IC are all matched, have very low noise and have very low input offset voltage. The resistors inside are also extremely well matched.
It would be extremely difficult to make one with separate cheap old opamps and ordinary resistors.

I guess medical scientists did that 40 years ago.

littletransistor · Dec 24, 2007

audioguru said:
The opamps in an instrumentation amp IC are all matched, have very low noise and have very low input offset voltage. The resistors inside are also extremely well matched.
It would be extremely difficult to make one with separate cheap old opamps and ordinary resistors.

I guess medical scientists did that 40 years ago.

Yes, it could be terribly difficult to make homebrew instrumentation amps. There are too much errors in building them.

Thank goodness I bought the INA126 and later the AD620 from my local online retailer. It simplifies everything at best, and also, gets everything done quickly.

raviram87 · Dec 25, 2007

thank u all for ur suggestions....

It would be nice if we can stop this discussion about which country is civilized and which is not... am an Indian and proud of it... am sure u all will be proud of ur country too... we all however belong to one universal civilized religion called humanity... lets all be proud of it....

merry christmas wishes to all my friends.....

i have tried my best to get AD620 and INA 126 from the net... hope i am able to get them.... will keep u updated...

audioguru · Dec 25, 2007

You are making a circuit that needs an intrumentation amplifier IC but you are trying to use very old opamps instead.

If you try to make a jet airplane then would you use a steam engine?

raviram87 · Dec 25, 2007

definitely not sir....

but the problem is we are not getting the ic here... i tried it... they are quoting a very high price... more than the price for which they are being sold on the net... for example an ad620 which costs 4.27$ on the net is being sold for approx. 13.75$ here... american $ i mean....

so am trying out all other possible ways of getting that IC here.... :-(

mvs sarma · Dec 25, 2007

raviram87 said:
definitely not sir....

but the problem is we are not getting the ic here... i tried it... they are quoting a very high price... more than the price for which they are being sold on the net... for example an ad620 which costs 4.27$ on the net is being sold for approx. 13.75$ here... american $ i mean....

so am trying out all other possible ways of getting that IC here.... :-(

the American taxes, international courier charges, handling charges at US and the customs duty if levied by the Indian authorities will all add up. Obviously they will be costly. Perhaps one has bear the cost if one desires lab works of reasonable quality and acceptability.

raviram87 · Dec 25, 2007

hmmm.... ok...

is there anyway i can get them for a cheaper cost? i tried in bangalore and chennai.... the best i coud find was for 14$ or so....

mvs sarma · Dec 25, 2007

raviram87 said:
hmmm.... ok...

is there anyway i can get them for a cheaper cost? i tried in bangalore and chennai.... the best i coud find was for 14$ or so....

Try at 080 4123 4126 Mr kirankumar
also perhaps TEXONIC might have.

audioguru · Dec 25, 2007

An AD620A costs $6.62US at Digikey and Newark here. The average worker must work for 13 minutes to pay for one.

raviram87 · Dec 25, 2007

@sharma...
thank u so much for ur help... will try contactng him....

13 minutes to earn a AD620.... actually i dont mind that doin it rite now....

audioguru · Dec 25, 2007

raviram87 said:
@sharma...
13 minutes to earn a AD620....

This is a HUGE world with different cultures.
Your standard of living is a lot different than mine.

mvs sarma · Dec 25, 2007

raviram87 said:
@sharma...
thank u so much for ur help... will try contactng him....

13 minutes to earn a AD620.... actually i don't mind that doin it rite now....

i confirmed availability of AD620 with Micro-components at 080 4123 4126 (Mr Kiran Kumar) and is available at approximately Rs200/- amouting to $4.5
Go ahead Mr Raviram

raviram87 · Dec 26, 2007

thank u so much for ur timely help mr.sarma....

this is amazing.... will immediately contact him....

mvs sarma · Dec 26, 2007

raviram87 said:
thank u so much for ur timely help mr.sarma....

this is amazing.... will immediately contact him....

Even if they give SMD take and use it you can easily wire it up. with little extra effort.

All the best

biopotential amplifier - help needed

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