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Topic: interfacing a sensor (Read 2 times) previous topic - next topic

retrolefty

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The connections + and - of the sensor,  you should connect the -ve to your arduino ground  and the +ve to your arduino analog input pin.


That is not how one reads a low level differential output from a Wheatstone bridge circuit. Grounding the -ve pin will just severally unbalance the bridge. See the ground connection at the bottom of the circuit, that is the only connection to be made to an arduino ground pin. The measurement to be made is the difference between -ve and +ve, not the absolute voltage of either of those pins, as they are both at nominally 1/2 of the excitation voltage applied to drive the bridge. An instrumentation type op-amp circuit is needed to both perform the differential measurement between -ve and +ve plus to add gain and also to convert the resulting analog output measurement voltage to a single ended type suitable for reading with an arduino analog input pin.

Lefty

Grumpy_Mike

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You will then read the voltage output by the device.

The point is that there is no voltage output from this sensor because the OP has not connected any excitation voltage to the other two ends of the bridge.
I am not sure why he and michinyon are ignoring the links to my diagrams, I went through all this in the late 80s, but if you want to find out for your self then go ahead. Just don't copy what I said and pretend it is your own work, and then get it wrong to boot.

kavya_mc

sir, i connected a simple opamp amplifier as per the circuit diagram in the data sheet and verified the result. Am still getting random interger values.(both positive and negative)and i referred the circuits in the  link that you sent me. but can you please tell me which circuit to use among them?
i have attached the circuit i tried to read the sensor with. The amplifier A1 that i used was non inverting opamp . output was random integers. can you please suggest any modifications?
thankyou

Grumpy_Mike

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i have attached the circuit i tried to read the sensor with.

No you attached the circuit that is in the data sheet. What did you use? It has to be different because that circuit shows no power supply connection.

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can you please tell me which circuit to use among them?

These were diagrams that accompanied an article.
http://www.doc.mmu.ac.uk/STAFF/A.Wiseman/Acorn/BodyBuild/BB86.html
It is BB37, but basically you need the big one with lots of bits in it.

kavya_mc

ok sir, one last doubt, should i connect the amplifier circuit thatyou suggested in place of A1 in the datasheet or at the output of the sensor?
thankyou for your replies and patience

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