Accelerometers

Accelerometers measure linear acceleration and also gravity; the two are indistinguishable. Thus they can be used as tilt sensors as well. Inexpensive 2-axis accelerometers are available which are constructed with MEMS techniques. MEMS gyroscopes are alos available for mmeasuring angular velocity.

The LIS2L02ASS4-TR accelerometer gives you a choice of +/-2g or +/-6g full scale. It needs only a single +5V supply. Its bandwidth is from DC to 1.5KHz. The output is low-pass filtered in most applications which do not need the full 1.5KHz bandwidth, using an external capacitor.

The chip is a bit challenging because it is available only in a surface-mount SO-24 package. Fortunately an adapter socket (Digikey A322-ND) can be used to give the chip convenient DIP-24 legs.

Soldering the chip into the adapter socket is a little challenging. Here are some tricks that make it easier. The more of these you can do, the better

• Use a very fine pointed soldering iron and fine solder
• Apply a bead of liquid flux to the pads, which will make the solder flow in under the pad enthusisatically
• Tape the chip down onto its socket adapter
• Have a magnifying lens or loupe available.
• Know which pins are not used.

The last point is especially useful. Start with pin 1 which is unused, so even if you get a solder blob connecting pins 1 & 2 that's ok. If the other pins are all aligned with their pads, pin 1's solder will hold them there.

Now solder only the other pins that are in use, as shown in red on the diagram. Solder one or two on the opposite edge as well, just for mechanical stability. Pins marked "reserved" should not be solder-blobbed to their neighbors because we don't know what they connect to inside the chip.