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Topic: Amplifying an analog read signal, the correct way? (Read 322 times) previous topic - next topic

Elessun

Hello all! I am trying to get a readout from a sensor that reports 7mv to 13mv to a multimeter but I can't seem to get a good read from an analog read.

Do I simply put in a transistor and provide power to the otherwise unpowered sensor? Or do I need an op-amp?

DVDdoug

#1
Oct 23, 2019, 04:38 pm Last Edit: Oct 23, 2019, 04:42 pm by DVDdoug
That's a very weak signal.  What kind of sensor is it?

How much precision do you need?

You can read down to about 1mV with 1mV of resolution if you use the optional 1.1V reference.    You can use a lower external reference but I don't know how far you can "push it".

The "perfect solution" would be an op-amp with positive & negative supplies.  There are "rail-to-rail" op-amps but I'm not sure how well they work when you get THAT close to the rail (close to 0V) with a single-ended power supply). 

Or, you could bias the op-amp. For example, with 1V of bias 5mV becomes 1.005V, etc. (not including amplification).    (I don't have a schematic handy for you).

...This is usually tricky because with a weak signal you're usually starting with a poor signal-to-noise ratio.  The noise gets amplified along with the signal, the amplifier generates some noise of it's own, and it may pick-up additional noise through the power supply or from electromagnetic interference, etc.

Paul__B

Hello all! I am trying to get a readout from a sensor that reports 7mv to 13mv to a multimeter but I can't seem to get a good read from an analog read.

Do I simply put in a transistor and provide power to the otherwise unpowered sensor? Or do I need an op-amp?
Come on, be sensible!  :smiley-roll-sweat:

Explain what this random sensor is, cite a web-link to its specifications or at least from where you bought it.  Why do you say it is "un-powered"?

polymorph

We can't help you.

Because you won't tell us what we need to know. Number one: what sensor? Part number, link to a datasheet.
Steve Greenfield AE7HD
Drawing Schematics: tinyurl.com/23mo9pf - tinyurl.com/o97ysyx - https://tinyurl.com/Technote8
Multitasking: forum.arduino.cc/index.php?topic=223286.0
gammon.com.au/blink - gammon.com.au/serial - gammon.com.au/interrupts

Paul__B

Three days now - looking like a "one-hit wonder"!  :smiley-eek:

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