# Tag Info

18

Only a sketch of a solution. Take all 3 axes into consideration. Acceleration due to gravity, regardless of tilt, will always be 1G, as a vector sum of X,Y,Z, no matter what the tilt. You can picture the acceleration at rest or steady motion as a point on a sphere with radius 1G. (If you are perfectly horizontal, that point will be (0, 0, -1) i.e. directly ...

16

An accelerometer is definitely out in terms of noise. A mechanical arm system, while potentially accurate enough, may well influence the injection scenario enough to render your results meaningless. I suspect a student struggling to control the position of a small syringe would be distracted by a large measurement arm, no matter how well balanced and low ...

15

In theory, is the position derived from accelerometer absolute? Ok, so imagine you're a sensor. All you can sense is acceleration. You're an accelerometer. Now you're at rest, or moving at a constant speed. You can't tell the difference, since Newton's laws don't allow that – an object at rest or in linear motion experiences no acceleration. Obviously, ...

12

TL;DR Basically, no, for most situations. Since acceleration is the derivative of velocity, integrating the output of an accelerometer should give you the velocity, however there are several flaws in that ointment(sic). Firstly, if you remember your calculus, integration leaves an arbitrary constant so you must know the initial velocity in order to ...

11

A Gyroscope gives the values of Angular Velocity (degrees/sec) in the three respective axis (Yaw, Pitch and Roll axes respectively). But whatever raw value given first by these sensors should be converted to sensible acceleration or angular velocity values by scaling. InvenSense Data Sheet of MPU-6050 says that we have to use different scaling factors for ...

11

The answers and comments you're getting are excellent of course, but I can add a little color. For what its worth, our sensorineural system uses much the same tools, and doesn't always get the answer right! We have 3D accelerometers (the otolith organs) and 3D "gyros" (angular velocitomers, the semicircular canals), and yet we suffer from all sorts of ...

10

The main issues with dead reckoning that I found while doing a senior design project similar to yours is that an accelerometer only measures acceleration. You have to integrate once to get velocity plus a constant C. Then you have to integrate again to get position + Cx + D. That means that once you calculate position from an accelerometer's data, you end up ...

9

An idea for low cost vibration monitoring: use your smartphone. I did this recently out of curiosity. Found an app that records my phone accelerometer to a text file. Leaving the phone on a table, I could detect the vibration of a diesel generator in the office basement. The generator vibration was only just perceptible by a person, and the phone could just ...

9

The first thing to do is to mount the accelerometer as far out on the swinging end (not the hinge end) of the door as possible. Then, of course, the accelerometer axis must be aligned perpendicular to the door. High pass filtering may help, but that requires leaving power on. Ultimately, you may not be able to do get what you want within the constraints ...

9

Your main mistake is in not treating acceleration as a single vector. When the car is at rest, that vector will always be 1 g upwards. Don't look at just the X component of the raw accelerometer data. Do the real vector math. But my problem is that when the device is on tilt (0g when no tilt) the acceleration is between (downward) 0g->-1g or between (...

8

I think an accelerometer and arduino is a great way to count the number of times the box moves up and down. It's a compact, reliable, non-contact way of detecting movement. It could work for movement as gentle as the rise and fall of your chest, when breathing, lying down, and certainly anything faster than that. You might get away with a simple threshold ...

8

The spikes seem to have a few common heights that are roughly related by factors of 2, which strongly suggests that they are noise-induced single-bit errors in the binary data. One good way to address this is to take the standard deviation of all the data, and then simply throw away any samples that are more than, say, 2σ from the mean. Another ...

7

That's a very bimodal distribution - not something you should see from vibration. My guess is you are either not reading the right data from the chip or you are interpreting it incorrectly. This part uses two byte values for the outputs - it looks like you may have the MSB and LSB swapped. Edit: I'm actually going to say that you almost certainly have ...

7

You'll also have bias in the accelerometers and noise in the gyros to deal with as well. And gravity shouldn't introduce errors in the angle measurements; on the contrary, the gravity vector provides an "absolute reference" that helps you zero out the accumulated bias of the "pitch" and "roll" angles. Yes, what you want to do is possible, but the poor ...

7

In general, no. Imagine throwing a ball straight up (and ignore wind resistance): once it's moving, the only force on it is gravity, which produces a constant acceleration. There's no way to know from the acceleration alone, when the ball has reached its highest height and started back down – the acceleration is the same throughout its path until it hits the ...

7

Several issues: This is the poster case for why you need to carefully chose which pins of the micro will be used in what ways. "I'm using them for interfacing to an LCD" is no excuse. Go use some other pins for the LCD that don't also have a special hardware function you need. Assign pins that use special hardware functions first, then assign general I/O ...

7

It is possible to use gravity to calibrate an accelerometer but it has drawbacks. Typically, for any accelerometer the Bias and Scale factor are calibrated. In this case the accelerometer output is measured in the +1 and -1 g positions, that is, measuring up and down. The average of those measurements is the bias, and the scale factor (in units of output ...

7

There is no lower limit to the frequency response of the acceleration to output transfer function. As the other answers have said, they detect orientation, which means detecting gravity all the way down to DC. However, be aware that all accelerometers, regardless of technology, suffer from the velocity to acceleration transfer function falling by 6dB per ...

6

What exactly are they? The error sources include zero-offset (bias) and scale errors (which tend to vary slowly) and noise. The prices of MEMS sensors vary from less than $10 to over$1000, and the magnitude of the error terms covers a wide range, depending on the quality of the sensor. The big problem is that integration is usually required to get from ...

6

You can disable individual axes on that part with CTRL_REG1. It doesn't say that this saves power. There's quite a lot of power-saving tips in that document, including a claimed consumption of 2uA. Probably the best thing is to put it into standby mode most of the time and use the "wake on acceleration event" feature.

6

I would err away from an accelerometer. To get displacement from an accelerometer means intergrating twice - once to get the velocity, and again to get the position. This means errors tend to accumulate. Also, the accelerometer would need to be attached to the needle, and it would probably be better to use a needle and syringe which looks and feels as ...

6

Maybe it would help to read the part of the datasheet where it tells you the output units? From page 12 of the datasheet: Linear acceleration sensitivity FS = ±16g 0.732mg/LSB So take the reading, multiply by 0.732 and then divide by 1,000 to get the acceleration in g. 1340 * 0.732 / 1000 = 0.981g edit - Note that is 0.981g NOT 9.81m/s, it's 20mg off, ...

6

An accelerometer senses XYZ movement So if it doesn't explicitly say it is a "rotational accelerometer" then it senses XYZ acceleration. In fact "rotational accelerometer" is a strange term, normally an accelerometer senses acceleration in one, two or three directions and something which senses rotation is a gyroscope. Note that the GY-85 and GY-521 modules ...

6

The vector magnitude is constant regardless of orientation, but you are applying offsets in one direction which throws off the symmetry. You can't calibrate away gravity in only one orientation and expect it to work for all orientations. Thinking about what you did and if you flipped it upside down instead of a slight tilt. Would you expect it to be zero? It'...

6

From what I recall, some accelerometers use 4_leg capacitive bridges, etched out of the top silicon layers to provide tiny suspended masses that respond to changes in force. Because capacitance measurements have no lower limits (using AC_stimuli to detect bridge imbalance), you should be able to sense down to DC.

5

Firstly it's important to understand how an accelerometer behaves in a gravitational field, such as we experience here on earth. An accelerometer does not measure acceleration, in the sense that it does not measure the change in velocity alone. It measures change in velocity plus gravity - which means that you need to take the measurement of gravity out if ...

5

@Olin Lathrop's answer is wrong. Unfortunately, I don't have the reputation to either downvote or comment on his answer. It's curious that he chose to claim that what is being achieved in the paper you link isn't physically possible... As madgwick's paper demonstrates it is indeed possible to maintain stable orientation estimates over long durations using ...

5

Note that setting up this study will be a big deal. Getting the instrumentation right will be a study in and of itself. I suggest poring over Medline or Google Scholar for a few days to see if anyone has done anything similar. Look at papers you've read that lead you to this area of research for guidance. Personally, I'd be looking toward ultrasound ...

5

As far as I understand, you will get the acceleration in [g] on each axis by dividing each of the 3 values you obtained by 256 (because your sensitivity is 256 counts/g). To avoid any problems with the division of integer numbers, I suggest you to do in this order, for each value: Convert the number into a signed long, to avoid any overflow in the future ...

5

As Chris suggests, a ball tilt switch is the standard cheap approach for detecting orientation. The lowest-cost option appears to be the SW-200D, available for under 5 cents in quantity: This will close a contact when the gold-colored lead is below the horizontal, and open it when the silver-colored lead is below the horizontal, with a hysteresis of up to ...

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