Cheap Accelerometers anyone?

Philldapill

So, I've been wanting to play with some acceleromoters for some time now, but haven't had the chance to do it with school, my other PropBoard project, and other things. Well, I've got time now. [noparse]:D[/noparse]

I got some LIS3LV02DL chips the other day and after 6 chip failures due to some bad solder paste, I've got the chip working, thanks to Tim Moore's object for a simliar chip, the LIS3LV02DQ.

This chip is a 16-bit, triple axis, 3.3V compatible, VERY precise accelerometer. I'm looking at the numbers bouncing around(slightly) on my TV screen and I've got a big grin on my face. This really is an amazing chip, and I have sooo many ideas for it. The only problem is, they are rather pricey. No where near what sparkfun sells them for, but still pricey - about $8 a pop in small quantities. I want to order at least 15 for myself, but the price drop is at quantites of 50 or more. I've made a small PCB for the chip with a mounting hole, and 4 holes for wires. I've got a pretty neat method for soldering these tiny QFN chips, so I can take care of that. Anyone interested in some of these? I think I can get the chip, PCB, and the chip soldered, mailed, etc. for about $12-$15. There are a few other components that I have to solder on the board, but not too much.

My last PropBoard project was a pretty big hassle, and thank you to everyone that bought some. My goal was accomplished, however, in ordering a large quantity and getting the stuff for myself, for dirt cheap. I'm hoping to do the same again, and get you guys some stuff for cheap while I'm at it. [noparse]:)[/noparse]

Just reply or PM me if you want a few

Post Edited (Philldapill) : 3/11/2009 9:51:28 PM GMT

SRLM

I say don't worry about the $3, and charge them for $15. I'll take a few at that price, but it would be good if you could test them before you send them out. Your mention of 6 chip failures before you figured out how to solder them correctly is honest, but confirmation of health on a final product would be appreciated. Anyway, keep us updated.

Philldapill

I'll definately test them first. All it requires is "plugging" them into my board and making sure they are sensing accurately. Those "failures" were actually me just trying to figure out how to solder QFN... I never thought an upside down clothes iron can be such a good solder station. A little solder paste, and the chips just align themselves!

jb1311

I'd take 2 @ $15.

Nick McClick

Hey oh! I thought you were just selling the chips. If they're breakout boards, I'd be interested. If you can make it a swap out replacement for Parallax's accelerometer (This one), I'd be interested in 10+ boards. (Although a 3.3v Vdd would be fine, I don't need the onboard regulator).

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Philldapill

Awesome guys! Nick, can I ask why you want a drop in replacement? In my opinion, that accelerometer is rather bulky. This breakout board would only have 4 pins(GND, Vcc, SDA, SCL). I was thinking having the pins come out as right angles - this way the pins are parallel to the board so that the board takes up very minimal space(like the original Basic Stamp).

If you guys have any suggestions as to what the board layout should be, by all means, suggest. Right now, the board size is about 0.5" x 0.5". Pretty small... Also, the chip itself can be driven with i2c or SPI, BUT the object that Tim Moore wrote, works strictly with an i2c interface. This is why there are only 2 data pins, and 2 power pins. It's simplier and more compact that way.

Again, suggestions are more than welcome. By the way, I played with the chip for a minute after class today... I'm blown away by the sensitivity. I'm wondering if it's actually TOO sensitive. I mean, I have it on the floor, and my foot steps cause the numbers to jump around a bit - that's 3 feet away on carpet!

Old man Earl

I'll pay for 2.
Earl

BTW, can you do a tutorial on QFN soldering ? I have several IDC gyro chips that are 28 pin QFN. Need a breakout board. You may want to look at this GYRO chip and offer it on a board.

Old man Earl

Oops...forgot the data sheet. here it is.

tperkins

Hello Philldapill, I need to downgrade my commitment to one, not two.

PS. By what means did you send the boards UPS, USPS?

Thanks, Tom Perkins

Old man Earl

I did find some cheep breakout boards for QFN here
http://www.schmartboard.com/index.asp?page=products_csp&id=125

Also, how about a 5DOF or 6DOF board. All I have seen are more than $100
3 Acl and 3 gyro would be great with a i2c or spi a/d converter on one board. I am building a quardocopter with a prop board and need some sensors !
Earl

SRLM

I second (or third or ...) the gyro or 6DOF board. It's really difficult to find a suitable triple axis gyro for a reasonable price. If you could get both the gyro and accelerometer package to less than $50, I'd buy a few, and I know some people who would also probably buy a few. I'm sure your project that you're working on (whatever it is) could benefit from some... [noparse]:)[/noparse]

Philldapill

Ok, I'm going to write a quick response before my computer spontaneously shuts itself off for the 100th time... Earl, I'm trying to find those IDG chips, but not much luck. Where did you get them? Also, a Quadrocopter is THE main project I want to do with these accel chips. I dream about those things...

Tom, I sent them out USPS First Class Mail... Using my insane inductive reasoning skills... I assume you didn't get the package yet?(uh oh... PM Me)

SRLM, I'm pretty sure I can get both a good gyro and accel chip wrapped up into a neat little package with a bow on top, for under $40 for sure(unless gyro's are $25 or more... We'll see.)

And guys, don't worry about any commitments yet. I'm just feeling the water to see if this would be a good deal for me and anyone else. I'm going to keep looking for these gyros. In particular, I'm going to try to find one with a spin object already written... unless anyone wants to make one? Anyway, thanks for the responses guys!

Philldapill

Whoa... I was joking when I mentioned gyros being $25 or more... The cheapest I found IS $25 in quantities of 50-99. That's the one you mentioned earl. It's not in the obex either... The other one I found that IS in the obex, is the MG1101. I'm having a very hard time sourcing it however. I'll keep you'll posted.

Philldapill

Oh yeah! I just found a single axis gyro from ST... They have "limited samples available for $2.50/unit", but it sounds like these chips will be a little more pricey than that once they go into production. Now, I'm just trying to figure out how to mount at least 2 of these units perfectly perpendicular to each other... Any thoughts?

http://www.st.com/stonline/stappl/cms/press/news/year2008/p2318.htm

SRLM

I don't think they need to be perfectly perpendicular. If you get two boards, and have them factory cut, you can (probably) make the assumption that they are perfectly square boards. If you mount one on the other to form an L or T such that the edge of one board is laying flat on the surface of the other board, it doesn't matter if it's slightly tilted or not. It will simply be a calibration constant that you'll have to think of (assuming that the axis of rotation matches that of the tilt). I think you'll have a larger error when you solder the chips on and let them 'float' into position.

Old man Earl

I got 3 of the IDG650 gyro's as samples from IDG in calf. I told them me and my daughter were working on a proj. Yes they are $40 in single lots. If we could get them for $25 each I'd be happy. Remember they are DUAL axis gyro's. So one of those (see data sheet I posted) a single gyro, a 3 axis accel chip (about $9) an 8 ch. a/d i2c chip, a few r's and c's , a pcb...the parts could come up to about $70. Now $30 for assembly, and you have a sub (or around) $100 6 axis gyro. Sparkfun 5dof is $110 and doesnt use the latest chips like the IDG650.

Look at the data sheet on it ! 2000 deg/sec resolution. I think even at $40 the chip is worth it because of the specs. I just dont know if the iron method of putting together this thing would be practical tho. Sparkfun says they may be interested in the design but the lead time is prob at least 6 mo.

See my post on the pcb breakout board that could be used. I think they would layout a board with 4 x 28 pin qfn chips for about $9 each. Right now the $9 board has 4 QFN breakouts. one a 16 pin, one 28 pin a 16 pin and one other.

The ST gyro sounds good for $2.50, and mabey we can talk them out of 50 or so at that price. I am sure we can layout a sub $100 6dof board with i2c a/d and all... Whats everyone think ?
Earl
Breckout board http://www.schmartboard.com/index.asp?page=products_csp&id=125

Philldapill

Just to let you know, Earl, I can make my own custom PCB's at my house. I'm limited to single sided designs, but making a batch of 20 boards shouldn't take me more than an hour or so. No need for those schmartboards [noparse]:)[/noparse]

By the way, IF(and that's a big IF), we can mass-order some of these gyros(lot of 50 or more) we can get the gyro down to $30. When you factor in the accelerometer, pcb, and gyro together on a single pcb, I think I could get these done for about $50. That's a pretty big "I think"... We'll see.

Post Edited (Philldapill) : 3/11/2009 2:46:49 AM GMT

Old man Earl

If you need any help doing this let me know. I have a full lab here and I am retired.(so I have the time) I like the iron method.
My quadcopter is physically coming together. I have th4 4 brushless motors and ESC's and props, and a 6 ch TX and RX. Prop board and been experimenting with the RX and servos on the prop board.
Earl

Old man Earl

Has anyone given any thought about a quadrocopters configuration ? an x config or a + config ? Think there is any advantage in either or how about a tricopter. One advantage in the tri would be one less motor and ESC and one less mounting arm etc. I am using ham radio antenna tubing for the arms because they will be sooo much stronger than 600 size heli boom tubes.
One other objective would be to protect the outboard props with some kind of cage. I want this thing as indestructible as I can make it because I have TRIED to fly heli's , even co-axil ones, and I am not too good. My main use will be for pic and video platform. End goal would be one that could take off and land autonomously and fly to gps points remotely and return with at least a 30 min Li-Po battery.
With all the things I want on this puppy, I'll be needing a 25HP outboard boat motor ! I'll show some pics of what I am doing soon. (need to clean up lab a bit first) I also have a 50' x 70' Manufacturing facility here to put something into production. MMMM...Homeland securty funds to get it started ? We are in the middle of New Mexico and have room to fly protos. My place is 1/2 mile by 1/2 mile 160 acers. Nearest neighbor is 2 miles away. Been working on this for several months now and can see a good product to come of this...Cheeper than the x6 tricopter at $14,000. and hopefully with better and more sensors on it. Gnd sevcing radar, ir thermopiles, gyros, accel, dgp barometric pressure for altitude.etc. Lets dream BIG..then scale back just a little !
Earl

Philldapill

I like your thinking Earl!!! What you're describing is something I've been dreaming about. At my university, there is this thing called the "Advanced Robotics Research Institute", or ARRI for short. I learned about it because one day before class, this graduate student was walking by with a quadrocopter he built and I immediately started jumping up and down clapping my hands and a few insane sounds came out of my mouth. I looked nuts, because I was nuts over this thing. I got to talking to him about it and he told me about how it works and what not. The thing cost him about $400 to build, even if it WAS university money!

My point is, I think that would be awesome to develope something like this and market it. My parents have a similiar building - 30' x 60' and virtually every tool I can think of.(Too bad I live in campus housing now...) I'm thinking about starting this project up and really rolling this summer. By all means, PLEASE post pictures, and ever scrap of progress you make with this thing. Quadrocopters make me act like a little kid on christmas morning.

Old man Earl

Well, lets all get together and make it happen. I know there is a lot of other people interested and hopefully we all can colaberate.
Earl

Old man Earl

I have been investigating optical mouse sensors. they have an 18 x 18 or 20 x 20 cmos sensor similar to camera sensors. Some have put lenses on them for optical sensing of horizon etc. I'll look more.

Philldapill

Sooo... Anyone want some prototype accelerometers? I'm getting some more chips, and going to make some breakout boards over the break. $5 gets you one. This is for the chip already soldered to the board. Only thing needed, is a pin header, or just solder to the pins and mount it with a screw.

The professional ones will be $15 since I'll have to buy the chips and not use my samples...

Post Edited (Philldapill) : 3/11/2009 9:44:28 PM GMT

SRLM

I'll take a few...

Philldapill

Well, I only have 6 more samples left, since I fried the others. I want to get these boards fabricated out to a real manufacturer, but then again - the total PCB size for even 50 breakout boards would be like 12.5 square inches... hardly worth the expense. So, a small change of plans. I'm just going to make the boards myself. The quality is pretty good, but it makes it slightly harder for me to solder the chips without solder mask.

So, home-brewed boards it is. $5/each for the sample ones I have, and when I run out of those, $15 a breakout board w/ chip and caps soldered. I'll post a picture of the finished board tomorrow when school is over.

tperkins

Hello Phill,

A) I have sent you a PM.

I would primarily be interested in a three-axis board, whether that's three chips or a single 3-axis device. If it were an 3 axis accell and 3 axis rate system, that would be excellent.

What price for such a 6 DOF board or sensor, if 50 were to be bought?

Thank you, Tom Perkins

Philldapill

This is a fairly educated guess, but I THINK if I can get the Dual Gyro's for $35(that's at the 50 unit price drop), again I THINK, I can get some boards made, with 3-axis accel, dual axis gyro, for $50. The Accelerometer driver is already written and works fantastic, so, the gyro driver needs to be written as well. Like I said, this is just an estimate, but I'm not seeing why that estimate should be too far off. However, I'm a broke(at the moment) college kid, and I don't think I can try another project like that, unless I had firm commitments, or cash up front from everyone. It would cost me about $42 just to order all the stuff, and at 50 units, is alot of dough... Maybe Parallax would be interested in carrying something like this?(hint hint)

EDIT: Just FYI to everyone, I'm seeing about 1% jitter on each axis with the LIS3LV02DL chip. I doubt that's much of anything for a kalman filter to take care of... It seems the jitter also decreases in percentage as the acceleration is higher. When I have the thing sitting on my table, the X and Y have a fairly consistant 1% jitter, while the Z axis is more like 0.1% since there is more acceleration on that axis. Just FYI.

Post Edited (Philldapill) : 3/12/2009 12:08:01 AM GMT

SRLM

Definately get some cash up front. It's $2500 worth of product, and if you don't sell it all (or at least ~40 units), you're in the pits. When you get it worked, be sure to post a final cost and platform specifications, and where to send the money. (Paypal, check, etc.)

Old man Earl

Well my new 6 ch tx/rx came today but no rc xtal...BOO...I need a72-6 xmit ch 29 or a 72-12 ch 56 rx ...I sure i'll find it. motors batts esc and props will be here soon. Been playing with the gps into the prop board with servos rxinputs and soon sensor data.
well, took my night pills so Im fading...us old guys do that......I remember when 63 was old...now thar im here, its not THAT old
Earl

rjo_

Phil,

I'm definitely interested in the accelerometer... regardless of specs. I would like 4, but I would order more. If you only have a couple left, don't re-order for me.

Rich

Old man Earl

Talk about cheep accl's. How about $14.95 at Best Buy ? Its a knockoff of the Wii numchuck ! It's called the EDGE for Nintendo Wii. It has a Freescale 8 Bit processor MN9sQE8CLC and a Freescale 3 axis accelerometer A7260 . The thing talks via SCL and SDA pins on the processor. Here is the wire color code and pinout. BTW, the processor has 7 more free A/D inputs (and some digital) we can use ! Here is the data on the processor.

http://www.freescale.com/files/microcontrollers/doc/data_sheet/MC9S08QE8.pdf?fsrch=1&WT_TYPE=Data Sheets&WT_VENDOR=FREESCALE&WT_FILE_FORMAT=pdf&WT_ASSET=Documentation

And the 3 axis part
http://www.freescale.com/files/sensors/doc/data_sheet/MMA7260QT.pdf?pspll=1


It also has a rocker ball and 2 push buttons if you want, But I cut the board in half (Cuts electronically very nice). So you end up with a board 1" x 1" with a 3 axis accl that talks to the world via SCL/SDA.

Now to write some code to talk to it !!!Nunchuck wires on the ckt board.....
Red > Pin 3 = VDD (3.3 Volt)
Yellow > Pin 7 = SCL
Green > Pin 8 = SDA
White > Pin 5/6 = Ground
Black > Pin 5/6 Ground Plane (VSS)

Post Edited (earl@uphi.net) : 3/15/2009 3:51:41 AM GMT

Post Edited (earl@uphi.net) : 3/15/2009 5:33:06 AM GMT