Sensors

ADXRS MEMS Gyroscope

Posted 1 Oct 2002 at 14:01 UTC by steve Share This

According to a story on smalltimes.com, Analog Devices is about to ship their long awaited ADXRS Gyroscope. The MEMS-based device will sell for as little as $10 - $30. While targeted at hand-held devices, the low cost makes it ideal for robot projects (nBot and autopilot come to mind). The ADXRS Gryo comes in a range of resolutions but all are in standard BGA packaging measuring 7mm x 7mm x 3mm and draw 5ma at 5 volts. A library of technical documents containing example applications of the ADXRS is available online. The full press release is also available from Analog Devices.


I hope they have an inexpensive development kit..., posted 1 Oct 2002 at 14:55 UTC by jeffkoenig » (Master)

...with an adapter board. BGA's are a little beyond my prototyping capabilities.

I found this interesting, from the site: "the same process that has been used to manufacture over 100 million accelerometers since 1993."

Would these 100 million accelerometers be found in automobile airbags? What other existing product uses these?

ZIF sockets?, posted 1 Oct 2002 at 15:53 UTC by steve » (Master)

I've seen ZIF sockets for BGA packages but I don't know how expensive they are. I bet they'll cost as much as the gyroscope! :-(

ADXRS versus Tokin, posted 1 Oct 2002 at 20:17 UTC by hudson » (Master)

I haven't had a chance to read through the data sheet yet, but I've already asked for samples.

The Tokin CG-16D angular rate sensor ("gyro") that we're using on the autopilot 2.2 boards has been End-Of-Lifed by Tokin, so we're looking for a new solution. It is a great part, but their customers were mostly buying the L34 3.3 volt unit instead. We could adapt our boards to it, but the solid state and better noise resistance of the ADXRS looks better.

My one complaint about both of them has to do with their sensitive axis. The Tokin can do three axis sensing with only two boards since it is parallel to the mounting plane, but the Analog part will require three boards since it senses perpendicular to the plane. That will add quite a bit of cost to our IMU design. I wish they would offer three axis versions of the gyros and accelerometers to save us the cost and hardship of orthogonal mounting.

This is going to be tricky to solder down on a PCB, posted 2 Oct 2002 at 14:09 UTC by earlwb » (Master)

I have put in a request for a sample or two also. But I do agree that this is going to be tricky to solder. My idea is to make a small PCB for the parts. Where the pads are underneath, I plan to have .020 plated through vias to the other side with pads as well. Then "somehow" holding the chip accurately on the PCB, heat up the pads on the other side of the pcb, and with a bit of solder allow it to flow through the via and solder the pins on the chip. I'll be using a dab of liquid flux for this, but only on the pads not under the chip itself. One problem is going to be hard to eyeball if the pads and measurements are correct as the little pins are under the chip itelf and not that close to the edge. I wish they'd keep the TSOP or TQFP packages. I hope they do have a eval board for this like the accellerometers.

how to solder bga chips, posted 11 Oct 2002 at 10:17 UTC by nevyn » (Journeyer)

Well, the normal way to do it is with reflow or wave soldering. Basically, add solder, place component, heat - the surface tension of the solder will move the chip into the exact position.

I suggest trying the following: *) design a board with the correct pads *) cover the board with lots of flux spray or liquid flux or something *) using either low temperature solder (silver?), solder paste or - with a lot of effort - normal solder shavings, cover the pads with a little solder *) Place the component as accuratly as possible *) put the whole lot in the oven set to an appropriate temperature for about 5 mins!

For normal solder I think you would need 300 degrees but I don't think ovens go up that high?! Mine does 270 I think which might be good enough. With silver solder or solder paste I think the temperature is lower so you may have better luck :)

Got my sample in, posted 8 Nov 2002 at 20:23 UTC by earlwb » (Master)

I received my sample, and .020 pads are too big, so I'll be trying the heat it up and hope it sticks method, as mentioned above. I happen to have a hot air SMD rework tool, so I think that'll heat up it good. Those little .020 in size BGA pins are tiny. They aren't making this easy for us anymore. If this keeps up, we'll have to figure out how to glue down dies and do the wirebonding ourselves next. Hmmm, hope somebody takes this as a hint and develops a reasonably low cost wirebonding machine for us.

It's alive! It's Alive!, posted 2 Dec 2002 at 16:42 UTC by earlwb » (Master)

I was successful at mounting my Hyro chip on a PCB. Plus the circuit works too. Really, really neat. I had a PCB layout done for me by ExpressPCB.Com, I then applied some flux onto the PCB and carefully placed the chip. Then I used a hot air rework station to carefully heat up the stuff and solder it down. Of course you have to carefully hold the chip in place to prevent it moving as the hot air flows under and around it. It took about three seconds to heat it up real nice. You could tell as the solder started flowing as the chip would drop down ever so slightly.

I am planning a project submission for the DPRG website detailing my PCB layout for a combo low cost Gyro/Accelerometer system on one PCB. Of course low cost is relative. Right now the Gyro chip costs $39.90 in single units, and the Accelerometer costs about $29.90 in single units as well. So we have about $20.00 for the PCB (piggy back with other layouts), $70.00 for the two chips, plus maybe about $10.00 for other assorted parts like capcitors, inductor, regulators, connectors, etc. So it looks to be about $90.00 to build one up. But then a while back another company wanted something like $4500 for a gyro chip setup. So in that case it is low cost.

But it is really cool, works nice, the gyro is real fast and very sensitive to small tilt changes. The Accelermeter allows you to compensate for the creeping gyro errors that occur in things like a two wheeled balancing robot.

I love it when things actually work. It is so hard to debug and fix things in the unknown area.

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