I just bought a new Arduino sensorkit, and while I love it, am finding some of the explanation info confusing. For example, with the accelerometer, the Arduino instructions say it is a Grove/Seeed unit using a Freescale chip MMA7660FC with specs of +/- 1.5g. I tried using the example Grove/Seeed library that Arduino links on the sensor kit website and cant make it work. Then I tried the Arduino sensor kit library itself, which is described as a wrap around of other OEM libraries and then explains it uses the library for accelerometer LIS3DHTR which has much higher g ratings, its obviously a totally different instrument. Anyway, with the LIS3DHTR library within the sensor kit library I get readings with the simple .ino example, although I don't know what the units are (g maybe?) with the unit at rest I get readings of roughly -1.0, 0.1 and 0.01 steady state (they vary a bit but that is the avg. Can anyone advise? What library SHOULD I be using? Shouldn't I be getting readings of zero for the three axes? Thanks, Steven Lightfoot
This is what you expect. If properly configured, the accelerometer library will report +1 g along any vertical axis, pointing in the upward direction, -1 g if the axis points downward, and approximately zero g for any horizontal axis.
Intermediate orientations lead to intermediate values along various axes.
The axial directions are usually printed on the sensor PCB.
Fair enough. Honestly that is a Homer Simpson Doh! kind of moment. Thank you. Do you have any comment on the library I should be using for this MMA7660FC?
You should use the library written for the chip you have, which is not entirely clear from your post. Please post a close up, focused pic of the sensor board.
Thanks, ouf. I now see what is going on. I bought the sensor kit mainly to get used to using instrumentation with Arduino, and its great. I do have applications for some accelerometers for vibration measurement, and I see this MMA7660FC wont really help (too low gs) but its definitely useful for orientation. Thanks for your comment. Any thoughts on the best library for this?
Cool thx, I will post a photo later today. This is the link to the Arduino sensor kit site. You can see they have a link at the bottom to the Grove/Seeed website where they describe the actual chip.
The issue is the Arduino sensor kit library explicitly says it uses a sub library for a different chip with very different g ratings, and this Arduino Sensor kit library v1.2.1 library works for me.
Now that I looked more closely (I am having a lot of Homer Simpson moments today its clear its really a LIS3DHTR unit, though maybe the chip is still MMA7660FC. So its more clear now why the Arduino library works. The LIS3DHTR library also says its rated for up to 16 g which is WAY better for my needs, which is great.
So I guess I have answered my own question (with your help) although I dont know why the Arduino sensor kit explanation and example page sends you to the Grove Seed site for the MMA7660FC.
