[volt-nuts] LM3900 (was: HP3458 ADC integrator) Instrumentation Amplifiers (3)

[Andre]

Hi, also have three AD623(?) IA's I purchased for a heart rate monitor.
Can find them as and when needed, pretty sure they are the ones featured in the Hackaday article.
At the time if the ECG worked the same circuit would get cloned and used for an EEG as the signals are a lot smaller but
in this case I'd use a Pi Zero or Arduino as the input as its already got onboard A-D's.

For this project the isolation requirements are insane, 0.1mA permitted leakage means you're limited to battery power and
even wireless charging is verboten. One big problem is the brain really does *not* like excess electricity, permanent damage is
quite likely even with careless use of a TENS machine etc.
Its feasible to use EM sensors based on old atomic clock "cores" to measure brain magnetic fields (maybe thats what DOC BROWN used)
but try getting more than one of them or disciplining them in the presence of Earth's magnetic field to make measurements.
Alas this project is going to have to wait until technology radically improves, as all the SQUID sensors I've run into use liquid helium and there are very few ways to get a piece of niobium-titanium that cold even using laser cooling and Linde refrigerators etc.
Ironically this is the main reason why quantum computers suchnas D-wave 2 or the IBM one are so heinously £xpen$iv£ as they need to get down to millikelvins so sit upside-down in the LHe vat with all the sensors far away from that little chip.

-A
________________________________________
From: volt-nuts <volt-nuts-bounces at febo.com> on behalf of Attila Kinali <attila at kinali.ch>
Sent: 01 March 2018 19:57
To: Discussion of precise voltage measurement
Subject: [volt-nuts] LM3900 (was: HP3458 ADC integrator)

On Wed, 28 Feb 2018 06:32:58 +0000
Andre <Andre at Lanoe.net> wrote:

> Can you make use of an LM3900? I have one here *somewhere*.
> I think its a quad Norton, not sure how long its been there for.

Theoretically yes, in practice you are better off using an opamp
that is not 40 years old and not as quirky as a Norton opamp.
You can buy standard bipolar opamps that beat those old beats
at all metrics, and they only cost little more, if at all.

The only place where these beasts really excell is that the
inputs are basically independent of the supply voltage, given
the maximum input current is not exceeded. Linear has a few
opamps that can do the same trick (though in a slightly different
manner), but they also cost a bit more.

                        Attila Kinali

--
<JaberWorky>    The bad part of Zurich is where the degenerates
                throw DARK chocolate at you.
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