MMA7260QT 3-Axis Accelerometer Wrist Control Device

Good Day All:
I want to use the accelerometer to trigger a transistor. I’m looking to activate a circuit by twisting of my wrist. I need this to be very simple! Can I simply hook the base of a transistor to the accelerometer output? I only want to trigger the transistor with a pretty sharp wrist movement so I will probably set the sensitivity pretty high, but how do I adjust the connection between the board and the transistor to fine tune the voltage trigger? With a wrist twist, how long would the transistor close my switch circuit? Does any of this concept make any sense?

Thanks very much,


It sound like your twisting motion might be better measured by a gyro than by an accelerometer, which will be affected by gravity. As soon as you want adjustable thresholds and durations, it’s not going to be that simple. I think the best way to go is to program a small microcontroller to do what you want, but if that is not something you want to consider, you could also use a comparator and a one-shot pulse generator circuit.

- Jan

Thanks for the reply. I’m unclear why a gyro would be better. If I twist the accelerometer and hold it in its new position, does the output voltage voltage spike high and return low, or does it stay high according to its orientation?

(I wanted to avoid any kind of micro to keep the unit smaller and less power hungry.)


Hello Shorpal,

The gyro would be better if you want to respond to angular motion in general without regard to orientation of your wrist. The gyro outputs a voltage telling you how fast it is spinning (angular velocity). Are you trying to trigger an effect based on a rotation angle of your wrist, or just twisting your wrist in at any angle? The former would require a accelerometer, and only work using gravity as a reference. The latter could probably done better with a gyro because it will respond better to quick motions. For example, on a balancing robot I made, I used an accelerometer to get the robot’s angular orientation over the long run, while relying on a gyro for the quick changes in orientation. The reason the gyro works better on short timescales, is because you can see large accelerations on a short timescale that don’t actually amount to much motion. Consider what the output of your accelerometer might be if you were shivering (It’s actually cold here in Las Vegas now.): your wrist might be accelerating very quickly, but actually not rotating with much velocity.

- Ryan

Hi, thanks for the response. I was thinking of a control that would be activated by a quick twist of my wrist, regardless of the actual position of my hand. What I am looking for is anytime I do a sharp twist (like the motion of twisting a motor bike throttle) I would momentarily close a switch. Do you think the LISY300AL unit would be better? The twist motion would have to be pretty aggressive to avoid false actuations.

Thanks again,

Hi again,

It’s hard to say what would be best, but I think you can get it to work with either one. Since you want it to work in any direction, you could try the gyro and see how it does. We sell a few different gyros, each with different sensitivities. You should think about how fast your hand is going to be going, and pick a sensitivity that makes sense. Also, keep in mind, with the gyros, you have to orient the PCB so that the correct axis is being measured. For example, with the LISY300AL, the PCB will end up being perpendicular to the palm of your hand.

- Ryan

Hi All,

I´d like some help from yours. The point is that I want to detect small movements (in any direction: x,y or z). I have a case with all circuitry and want to detect if someone tryed to take it out from its home position (e.g.: I place it in a wall and do not want this unit to be removed from this place). I was thinking to use an accelerometer (like MMA7260QT). In reality I have bought Pololus kit. I use MSP430F2274 (from Texas Instruments). The code was based on Freescale AN3397. The first results seam very strange: big variation without moving accelerometer. I want to send an alert only if accelerometer move (e.g.1 cm) afar from its home position. A gyro is better? Does anyone has a complete example code to this accelerometer? Thanx in advance


Hello Arquimedes,

In general accelerometers and gyros have some noise on their outputs. Are you detecting a larger analog voltage when you try to move your device from the wall than when it is just sitting there? If so, try triggering at that higher voltage reading.

- Ryan

Hi Arquimedes,

Although I am not from Polulu - I do have a simple suggestion that might be assistance to you and requires no
microprocessor control. Assuming that you just want to build/implement a simple tamper detection alarm, you may find the
following idea useful.

About 10 years ago, I built a bike alarm using a simple 555 timer , amplifying transistor and a loud piezo siren
(the smoke detector grade). The motion detection mechanism where two simple mercury tilt switches mounted
in perpendicular fashion and where carefully set in a clear silicon sealant. Accelerometers where not around then,
at least an affordable price.

For a kill switch I used a 2.5mm stereo plug (shorted the pins) and a matching female socket. When ever I wanted to shut off the
alarm I just had to plug the socket in. Whenever I wanted set the alarm, I placed in its location and pulled the plug out. The 555
was wired to respond to closed circuit (ie this 2.5mm plug switch).

The trick was to remove the circuit (mounted in a jiffy box) in a certain direction and inclination so as not to activate the alarm.
However, the intended parties will receive an ear deafening surprise for a minute or so. It still works to date.

Obviously you can make several variations on this. Instead of activation a piezo/siren, you can use the 555 output pin with a signal transistor
to boost it to the level that you want. SImple enough! Very cheap to build! very effective!

I think I still have the circuit schematics if you like. Anyway thats my 2 cents worth. Hope I am not encroaching on Pololu’s


Not at all. This forum is intended to be a place where people can ask questions and share information about robotics and electronics. We welcome contributions like your post above.

- Ben

Hello Carl,

I need an accelerometer in a circuit I have designed a time ago. This circuit is based on MSP430F2274. It´s important to alert when someone try to take the circuit out of its home position. Of course, there should be a threshold to be determined experimentally (to avoid false alerts due to natural movements). I based the code on AN3397 (from Freescale). If you take a look on it you will notice some mistakes but even correcting those mistakes my readings are very unstable. If you have worked with MSP430 and this accelerometer and could help me I will be very grateful. I can send you my code if you need to check what I´m doing.