Operational amplifier in moisture sensor module


I'm using a moisture sensor (SEED_1010) wich has an operational amplifier in it.
What exactly does it do? Ive read that it is an differential amplifier or something.
I have no idea what it does, ive searched multiple sites but I can't understand them.

Would anyone be possible to explain it to a newbie?

I'll add the module scheme


Also I can use the sensor as analog or digital.
What is the difference??
They will work the same no?

Thank you

That is an op amp comparator circuit. It will switch states when the voltage on the + input crosses the voltage threshold set by the voltage divider on the - input.

The sensor is digital only and the threshold is fixed.

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Thank you for the reply,

I'll check out the link about the op-amp.

But the sensor can be used as analog no? It has an analog pin and is connected to my arduino uno on the analog pins.

Here is a tutorial about op-amps: Using Operational Amplifiers in your Arduino project

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I cannot see your sensor nor could I find a whole schematic so all I have to go on is what you posted. Post a link to the sensor data sheet and I can better try to answer questions about it.

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Here's the datasheet
Seeed_101020008-1217463(vochtigheid sensor).pdf (891.8 KB)

Thank you, I'll check that out as well!

The data sheet does say that it has an analog output. But the schematic that you posted is not in the data sheet, that I can find.

The photo shows a transistor on the board. If it had the comparator on it there would be a tiny 8 pin chip instead or as well.

So, at this point, I am not sure.

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1: The diagram does NOT show a comparator, the feedback is to the - input; for a comparator it would be to the + input. Also a comparator has a logic output, the output here is marked A0 which to me would indicate its analog.

2: Yes the schematic has no relevance to the datasheet which as you say clearly shows a three terminal device, likely a transisiitor.

3: the schematic shows 1k resisitors which is an unusually low value for an op amp circuit.

We have a saying the OP might find useful: garbage in garbage out.

Here is what appears to be the correct schematic for the Seeed Moisture Sensor:

Nope, that would be the case if the was a dot where the feedback resistor path crossed the positive rail, but there isn't. This circuit uses negative feedback, and without
knowing exactly what the sensor itself is its hard to figure out what its actually supposed to do.

Of course if could be a mistake in the drawing and its a comparator - that's actually all too likely (there are missing dots on the lower part of the circuit for instance)...

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