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2-Axis Acceleration Meter using an MMA7260QT

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Madgyver

Thu May 10 2007, 02:50PM

Registered Member #177 Joined: Wed Feb 15 2006, 02:16PM
Location: Munich, Germany
Posts: 214

I want to present my latest project, an 2 Axis Acceleration meter using a MMA7260QT Sensor and a MC68HCS08QG8 microprocessor both produced by freescale.

This project is not entirely genuine, as I bought the PCB boards as a kit from Elektor (although just the boards an I had to buy all the parts and solder everything myself

). Also the software is provided by Elektor, but I modified it for greater sensivity.

The MMA7260QT can be arranged for 1.5g , 4g or 6g range. 1.5g is what I am using and is suitable for car movement, jumping around and does not need a jet fighter or roller coaster for testing.
Actually the sensor is a 3-Axis type but this project only uses 2. For each axis there is an according pin which will vary its voltage according to the meassured acceleration.

The MC68HCS08QG8 samples these voltages and translates it to 12 LEDs arranged as an cross.

A63ddef08ec881cf68afb69f7b471bbc

The Processor is the 16pin IC on the right. The Sensor is on the left in an QFN-16 Package pre-soldered on a seperate PCB.

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The whole thing in action.

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This is the programmer, pretty neat for 9 Bucks. Comes with Codewarrior as Development software.

[Edit: Image size]

Ragnarok

Thu May 10 2007, 03:24PM

Registered Member #659 Joined: Fri Apr 20 2007, 09:14AM
Location: SW Hertfordshire, UK
Posts: 75

Pretty nice.
I could probably use a programmer like that one you've got there. The number of interesting projects I could start...

1.5G wouldn't be a lot of use for the sort of G forces I sometimes use in a typical day. It's not uncommon for these to reside in the four figure region. (Spudguns, if you're wondering).

Other than that, I can't think of any G-forces I would be interested in measuring...

Madgyver

Thu May 10 2007, 03:33PM

Registered Member #177 Joined: Wed Feb 15 2006, 02:16PM
Location: Munich, Germany
Posts: 214

Thanks ^^

Well 1,5 is the smallest value possible, 6g Maximum. Freescale also produces sensors for the 160g Range which is suitable for Missiles, jetfighters and everything else.

Are you sure about your 4 figure region (so, 1000g acceleration for example) ? I have never read about such high accelerations in the field of Engineering, not even when it comes to mortars or artellery.

Tom540

Thu May 10 2007, 09:34PM

Banned on 3/17/2009.
Registered Member #487 Joined: Sun Jul 09 2006, 01:22AM
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Posts: 617

HI,

Just curious. What language do you use to program for that thing?

Madgyver

Fri May 11 2007, 01:21AM

Registered Member #177 Joined: Wed Feb 15 2006, 02:16PM
Location: Munich, Germany
Posts: 214

Well I am using C in this example. It just makes things easier for me.
Programmming menues in C is quite relaxed compared to in assembler. Although it is possible. But klicking through a menue in order to select a operation mode, doesn't ask for high efficient or high speed code (which is almost only possible in assembler) but asks for foolproofness and easy ways for modifications (easy to do in c).

I have to correct my statement about large g-forces. There are a lot of machines which have to deal with very big accelerations, like sewing needles (which is quite surprising to me). These accelerations are only so large for very light parts an can easily reach the 1000g line.

But anway, for larger machinery like cars, or so 6g should be sufficient. My next Goal is to incorparate an LCD display, so I can actualy read out the exact g-forces.

[Edit: Double post]

Ragnarok

Fri May 11 2007, 09:49PM

Registered Member #659 Joined: Fri Apr 20 2007, 09:14AM
Location: SW Hertfordshire, UK
Posts: 75

Sewing machine needles? I'm surprised.

Possibly more surprising, but true, the acceleration of some projectiles I use (for example, wadded paintballs, which are relatively light) can potentially reach 10,000 G to 20,000 G at some points in the barrels of my most powerful spudcannons (depending on air pressure), assuming they don't shred on the way out (which is not that uncommon).

The muzzle velocity of such rounds is nearly pushing whole Mach numbers, but the likelihood I will actually break ever the sound barrier with any of my cannons is low.

Actually, that's an idea for a project... I could try another homemade chronograph, and see if it's any more accurate.

Steve Conner

Sat May 12 2007, 01:56PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Is it even possible to break the sound barrier in air with a cannon powered by compressed air? Surely the pressure wave that shoots the projectile out is the same thing as a sound wave. Don't you have to use a gas with a higher speed of sound, or combustion?

Ragnarok

Sat May 12 2007, 08:27PM

Registered Member #659 Joined: Fri Apr 20 2007, 09:14AM
Location: SW Hertfordshire, UK
Posts: 75

I'm rather in two minds about the matter.

Physics seems to place limitations on breaking the sound barrier, but there are some reported cases of supersonic ammunition from pneumatic spudguns using compressed air. This may well mean that my interpretation of the physics is slightly flawed, as arguing against evidence isn't a good thing.

These multiple claims are compared to only one fairly doubtful claim (but from a typically reliable source) from a gas combustion cannon.

When you get up to solid propellants or hybrids (for those that don't know, a hybrid spudgun uses a compressed flammable gas mixture to achieve far higher combustion pressures of several hundred psi), there are many more cases of supersonic projectiles.
It's still being confirmed, but there is a claim of a chronograph reading of 2700 fps (About Mach 2.5) for a potato from a 55 foot long hybrid cannon.

It's hard to do, but it is apparently possible with enough pressure, a good valve, a light enough projectile and a long enough barrel.

But, indeed, you are right. The majority of supersonic claims come from cannons using a form of combustion, or using helium.

Conundrum

Sat May 12 2007, 10:30PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059

Hmm. I have some free samples of the ADXL202, as well as some breakout boards someone gave me.

Might be worth building a mini datalogging accelerometer for various reasons, as well as a Wii-clone R/C car controller.

-A

Madgyver

Sun May 13 2007, 03:24PM

Registered Member #177 Joined: Wed Feb 15 2006, 02:16PM
Location: Munich, Germany
Posts: 214

Steve Conner wrote ...

Is it even possible to break the sound barrier in air with a cannon powered by compressed air? Surely the pressure wave that shoots the projectile out is the same thing as a sound wave. Don't you have to use a gas with a higher speed of sound, or combustion?

Interesting point, In physics class we have been discussing the same thing (well, not spud guns but Air-Rifles). According to our physics prof. It is possible because the speed of sound and the probagation speed of the pressure wave are truely the same but are dependable of the temperature.

I cannot recall all mechanisms, but as long as the air in the pressure chamber has a slightly higher Temp as the surrounding Air (during decompression) it is said to be doable.

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