Gyroscopes Still Seem a Bit Like Magic

I remember a gyroscope toy my Dad bought me and showed me how to use. I could make it balance on a string, support it by only its end (like magic), and feel it resist when I tried to rotate it. Now I understand the physics, but it's still a bit magical. Today we find gyroscopes and accelerometers in toys -- how times have changed.

Mechatronics engineers -- and anyone who has owned a gyroscope toy -- should be interested in several announcements of sensors. These new sensors rely on devices that use micro electromechanical sensors (MEMS) to create accelerometers and gyros.

Sensor Dynamics, for example, has an improved version of its 3-axis SD746 combination sensor that measures angular rate of change ( plus or minus 2048 degrees/second) and acceleration ( plus or minus 8g). The calibrated and temperature-compensated sensor fits in a QFN-40 package that provides an I2C or SPI interface to a microcontroller. The company also sells a small demonstration board.

When the sensor package experiences accelerations and angular changes, the capacitance of the individual MEMS sensors changes proportionally. Internal signal-conditioning circuits and a sigma-delta analog-to-digital converter send measurements to a digital-signal processor that filters, makes bias and sensitivity adjustments, and compensates for temperature changes.

The DSP generates an interrupt signal when it detects changes, so a host MCU can obtain new information via the serial interface. Engineers can program a threshold value for acceleration and angular rate of change so the MCU doesn't get overwhelmed with small changes that don't affect operation of the product. Because the sensor chip takes measurements continuously, an attached MCU can obtain data whenever designers need the values at some point in their software, perhaps to provide a baseline value after, say, five minutes of inactivity.

STMicroelectronics has just announced a small evaluation board for its LPY410AL low-power dual-axis MEMS gyroscope that measures angular rate of change on roll (x) and yaw (z) with a maximum of 100 degrees/second over a standard -40C to +85C range. The sensor provides analog outputs for each axis that has a 1.5V potential at rest. Engineers can choose either a 1X or a 4X output. At the maximum rotation rate, the 1X signal puts out 1.75V (2.5mV per degree/second), and the 4X signal provides 2.5V (10mV per degree/second).

ST recommends using an external filter on these two signals. You can buy a small demonstration board for the LPY410AL family of gyroscopes. The board lets you choose either analog or digital outputs.

Click here to watch a five-minute video of how gyroscopes work in space. The astronaut demonstrates how a CD player acts as a gyro and then connects three gyros to stabilize a flashlight.