interfacing a sensor

yes sir I have connected the sensor outputs directly to arduino.......
can you please tell me what the bridge exciter circuit is.?
Also I wanted to know if the PC can detect two arduino boards simultaneously connected to it?
thank you

On page 2 of the data sheet at the top there is a diagram. Everything inside the dotted line is your sensor. Everything outside the dotted line is your exciter circuit. In this case it consists of an amplifier and voltage reference that powers or excites the bridge circuit.
However the data sheet also says you get 50mV full scale output from the bridge. That means that at the maximum pressure output you will only get a reading of 10 from the arduino's A/D converter. So it is not very suitable for direct connection.
This sort of sensor needs an amplifier if it is to be of any practical use.
This is a link to the sort of amplifier circuit you need:-
Imgur

Also I wanted to know if the PC can detect two arduino boards simultaneously connected to it?

Yes it can but only one can talk to the serial monitor built into the arduino IDE. The second will have to use another terminal emulator like freeTerm.

i connected 2 arduino uno boards to laptop and tried loading blink sketch by opening 2 arduino IDE windows. it worked on one board with COM 15. but for the other its not. i tried selecting COM 4,5,6,9,10,11. but it is showing the error as "avrdude: stk500_getsync(): not in sync: resp=0x00" what should i do so that I can work on both boards simultaneously?

I don't understand, when you say you want to read the sensor, and then send a message to the arduino if it changes.

Isn't it the arduino which is reading the sensor? Do you want to send a message to another arduino, when it changes ?

You have connected your sensor wrong.

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

You will then read the voltage output by the device.

The other problem is, the output of this device is 50 millivolts at full scale. On the arduino analog input, this will give you a reading of between 0 and 10 ( counts out of 1023 ) only, because the full range of this device is only 1/100th part of the full analog input range 0 to 5 volts.

The actual values you got, are the difference between your sensor1 and your sensor2 , which is 5 or 6 counts on the examples you got, so it actually looks like it is working.

You can improve the effective A/D range by understanding and using the arduino AREF pin. You could also use an external amplifier circuit using an op-amp to increase the size of the signal which the arduino is receiving.

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

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.

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

testckt1.docx (31.3 KB)

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.

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.

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

You do not need A1 if you use that circuit I posted. Just connect it up like the schematic tells you to.

thankyou sir..
now that I have the sensor readings, i have two questions.
1.I want to read the data from arduino to matlab,so once the arduino is programed to read the sensor ,if i disconnect and connect it again can i directly read it to matlab or do i need to run the program on arduino through arduino IDE again and again?
2. any information on how to read and plot the data on matlab will be helpful...am not satisfied with whatever i got from browsing.
thankyou.

Once an arduino has a program in it that program will run every time power is applied. There is no need to keep reloading it.
Sorry but I do no use matlab.

sir, can you provide me with some information/links on cost comparision of various "contactless position sensors" prevalent in the industry.
thankyou.

What sort of position sensors and what sort of range and precision? Industrial sensors tend to be very expensive due to how robust they ave to be.

sir ,contactless linear position sensor based on magnetostriction or optical nature or inductive sensor, anything sir. I just need a general idea of cost of the existing contactless linear position sensor.
thankyou

Most industrial transducers are very expensive and the vendors tend not to put the prices on line. You have to ask them for a quote like this one
http://www.pennyandgiles.com/contactless-linear-position-transducer-pd-50,3,,.php
Ask them for a quote

hello,
i need to program my arduino to store a look up table, and as and when it reads a value from the sensor, it needs to go through the table and display the value if it finds a match in the table. can anyone provide some suggestion?..
thankyou

kavya_mc:
can anyone provide some suggestion?..

Yes several.

  1. Start your own thread with this question.
  2. Learn about arrays.
  3. Learn how to access each element in an array using a for loop.
  4. Think if you need or can have an array entry for every possible input value. Think about interpolating between two entries.