I have a Wheatstone Bridge that I need to amplify. I'm not particularly familiar with it, it's the first time I'm playing with it and I have just the basic skills in electronic...
I have a Arduino Pro Mini 5V.
Basically what I have is a sensor, when I give him 5V in input I got 2.5V on the two other pin out. When I play with the sensor, one pin goes up (e.g. 2.6V) and the other one goes down (e.g. 2.4V).
I need to amplify this signal to be able to detect millivolt.
Do you know if this component INA128 can do the job?
I'm not sure about the "Supply Voltage Range", I need to put -5V and +5V ? Is it possible with my Arduino?
A wheatstone bridge goes well with an instrumentation amplifier. You can use the INA128 or INA125.
There are also digital ADC chips.
The Arduino Leonardo and Arduino Mega can be set as instrumentation amplifier with a gain without extra hardware. That is not often used.
Tell us what your project is. Is it a air pressure sensor or a load cell ?
I have a sensor that mesure the bending. The only things I know about it is that is it a full wheatstone bridge and that I should use a diff amp to see the bending.
Today I'm able to see the diff but without an amplifier it's almost impossible (I have to push hard), I need to detect micro change.
Here is a plot of what I got if it can help, but I'm not sure...
Without any mouvement both SP & SN are at 2.5V. When I started to push on the sensor they increase & decrease. For now, I calculated the diff via the software (subtraction of two analog channels).
A single strain gauge has noise and its value depends on the temperature. That is why often two strain gauges are used, one is pulled out, the other one is compressed. Those two together in a wheatstone bride (with two normal resistors) can give accurate results.
A load cell is the same. It measures the weigth by measuring the bending of a metal beam.
If you search for arduino with INA128 or INA125 and load cell or weighing scale, you probably find a few projects.
How much wires do you have ? Just the 4 wires of the wheatstone bridge ? Can you make a photo of the bending thing with the wires ?
In the datasheet is a simple example: Figure 31.
This is the page of the manufacturer : http://www.ti.com/product/INA128
You could set Ref to a voltage of 2.5V with two resistors, but I'm not sure.
For microcontrollers without an analog-to-digital converter or when you want a higher-precision ADC, the ADS1115 provides 16-bit precision at 860 samples/second over I2C. The chip can be configured as 4 single-ended input channels, or two differential channels. As a nice bonus, it even includes a programmable gain amplifier, up to x16, to help boost up smaller single/differential signals to the full range.
Actually, I don't think the ADS115 would work without op amp amplifiers. It would make more sense to just build an op amp diff amp and use only one input on the ADS1115 . At least that way you'd get the 16-bit precision.
raschemmel:
Actually, I don't think the ADS115 would work without op amp amplifiers. It would make more sense to just build an op amp diff amp and use only one input on the ADS1115 . At least that way you'd get the 16-bit precision.
The ADS1115 datasheet is confusing (to me).
It seems to be a 15-bit A/D (7FFFh max).
It only seems to be 16-bit if two inputs are used in differential mode.
Maybe someone can elaborate.
Leo..
Look at the code in the ADS1115 Library. The default device selection is the 12-bit ADS1015. To use the 16-bit code you have to comment out the 12-bit device selection and remove the "//" in front of the ADS1115 selection line.
16-bit resolution is 216 = 65536 => (0 to 65535 = 65536 possible values because 0 counts as a possible value.
The connection is radiometric so the quality of the top rail (like the Arduino 5V or 3.3V) is not important.
I'm not familiar with that usage of the word "radiometric" as it applies to electronics.
If you used the word "differential" then I wouldn't have any question. Since a wheatstone
bridge is a bridge, the parameter being measured is the voltage drop across the strain guage resistors so the only difference the Vcc is going to make is a matter of degree.
If by "quality" , you mean how well filtered or regulated (ripple etc) it is , then again I think I would understand what you mean. If you are just saying it doesn't matter how "noisy" it is , then I couldn't comment , not having actually used a wheatstone bridge in the last 30 years...When I did use one, I can assure you I was not thinking about "noise". (mostly because I didn't know if it was relevant)
Sorry it was a typo, should have been ratiometric.
This means that the stimulus at the top of the bridge is also the positive reference to the ADC and the connection at the bottom of the bridge is the negative reference for the ADC.
This way the ADC always has the same reference range as the voltage actually applied to the bridge.
This ensures that the delta from the bridge output remains the same number of code regardless of variance in the top rail.
The noise on the rail could propagate through but this device has very good filtering combined with the low pass filtering that is part of the Delta Sigma ADC.
Sorry it was a typo, should have been ratiometric.
Ok, now that makes sense. The measurement error due to variance in stimulus voltage is neutralized because the measurement is with respect to the stimulus supply, a change in supply voltage results in a change in measurement in the opposite direction neutralizing the error ?
I know this is an old post but the information isn't old. The best place I have found for the info requested if it can help someone else is Transducer Techniques, LLC they are helpful plus they have all the technical data on the Wheatstone Bridge.
