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Topic: Reading 0-100 mV signal (Read 3437 times) previous topic - next topic

danb35

After messing around more with the LM358s and not getting expected results, on the advice of an EE friend I'm looking into an instrumentation amplifier.  The AD623 is a rail-to-rail device that will work in a single-supply mode, and seems to be giving much more sensible results.  It is, of course, quite a bit more expensive than the LM358, but a few dollars each is still pretty reasonable.  Thanks again for all the help on this.

polymorph

You don't need a rail-to-rail Op Amp, you need a differential amp.

http://forum.arduino.cc/index.php?topic=205229.msg1567471#msg1567471
Steve Greenfield AE7HD
Nick Gammon on multitasking Arduinos:
http://gammon.com.au/blink
http://gammon.com.au/serial
http://gammon.com.au/interrupts

knut_ny

an "opamp" IS a differential amp.
Any rail-to-rail able to run from 5V will do for this job.  Find the cheap one, add a handful of resitors (and a cap or two) and calibrate.
Ny

polymorph

OK, an Op Amp wired as a differential amplifier. The circuit that the OP posted is wired as a single ended amplifier.
Steve Greenfield AE7HD
Nick Gammon on multitasking Arduinos:
http://gammon.com.au/blink
http://gammon.com.au/serial
http://gammon.com.au/interrupts

danb35

Although an instrumentation amplifier is not an op-amp (per Analog Devices' app note on instrumentation amps), what's the practical difference, in this application, between using an op-amp wired as a differential amp, and using an instrumentation amp?

TomGeorge

http://www.siliconfareast.com/inamps.htm

Hi, hope this link helps with op-amps and instrument amps,

Tom....... :)
Everything runs on smoke, let the smoke out, it stops running......VK3DMK

polymorph

Quote
Of course, an operation amplifier may be utilized as an instrumentation amplifier.
Steve Greenfield AE7HD
Nick Gammon on multitasking Arduinos:
http://gammon.com.au/blink
http://gammon.com.au/serial
http://gammon.com.au/interrupts

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