Tilt/inclination/angle sensor

J

JaniM

Member
Hi,
I'm new here and searched topics. I need sensor that measures angles or distance. What I'm doing is levelling system to car's airbag suspension.
I found APC-3 rc subs levelling module. But I'm looking for some other solutions.

The system would be next:
*four pressure sensors, one every bag
*sensors measuring cars level/angle
* picaxe-40x controls
* lcd
* buttons for presets ..

I would need advice for programming later. I'll make own topic for that project.
First project is temperature controlled pwm control for DC motors.

Jani
 
M

MBrej

Member
Hey, you could use accelerometers to measure the angle of tilt. An accelerometer responds to gravity, so you can tell how much tilt there is by the reading. If the axis is aligned perfectly vertically, the accelerometer will give its maximuim reading, and then as it is tilted the reading will decrease.

Most accelerometers give an analogue reading, so it would need to be connected to a analogue input of the PICAXE, which would read the value and decide what to do.

However, if it is in a car, the accelerometer will respond to bumps the car goes over, but if you were to add another accelerometer horizontally that may solve some problems (or create more possibly) although im not quite sure what your application is.

Matt
 
J

Jaguarjoe

Senior Member
You can get Freescale Accelerometers for free on a sample basis. Try a "MMA7360LT" it's a 3 axis analog sensor. Only hiccup is that they are SMD.
 
C

Cruiser

Member
I've used the DE-ACCM2G from Dimension Engineering with an 18X to good effect.

It makes use of the Analog Devices ADXL322 surface mount device but mounts it on a small PCB that you plug into a normal 14 pin DIL socket.

It provides two analog outputs that can be read accurately using the PicAxe's READADC10 function.

Check out dimensionengineering.com and analog.com for data sheets.

Chris.
 
P

papaof2

Senior Member
For measuring distance, there are ultrasonic sensors with a variety of ranges. For very small distance changes, a linear Hall effect device might be appropriate. It depends on the total distance between surfaces and how much change in distance you need to measure.

John
 
J

JaniM

Member
Thanks for ideas. The application is a car.
That DE-ACCM5G is intresting. I have to search where I can buy it.

Cruiser, what kind setup you have? Could you give your code?
 
B

BCJKiwi

Senior Member
Order direct from Dimension Engineering. You really want the 2G version as you are looking for level so want the maximum resolution you can get.

Set up the rig perfectly horizontal and mount the DE-ACCM2G horizontally and adjust (or zero in software - can supply a simple code snippet for this if you need) to show midpoint.

Any subsequent variation from true horizontal will show on the X Axis and/or Y Axis.
 
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J

JaniM

Member
Why 2g? Isn't 5g more accurate?

I found inclinometer from here.
http://www.vti.fi/midcom-serveattachmentguid-30e230919288bbb060588d83d7501b7f/SCA100T_inclinometer_datasheet_8261800A.pdf

Which is better, inclinometer or accelerometer? The basic idea is same, am I right?

I found also accelerometer, its 20e here.
http://www.vti.fi/midcom-serveattachmentguid-6908329cb1ab006eb0bf55cb935ac0b6/sca3000_e02_datasheet_8256000a.02.pdf

http://www.vti.fi/midcom-serveattachmentguid-1ae51856ebc94595b8f33d7a6699d969/SCA121T_Inclination_sensor_rev_4_021106.pdf
 
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B

BCJKiwi

Senior Member
As I understand your opening post, you want to test for level.

Accordingly you want to see as much change in the readings from the sensor as you can. As this is for a tilt application rather than vibration or acceleration, then the number of G will be very small. If the vehicle is tilted steadily from horizontal to vertical there won't be more than a 1G reading!

Accordingly you will get the biggest difference with the 2G device.
A study of the data sheet shows the 2G sensor has a change of 750mV per G at 5V supply. The 5G sensor has a change of 312mV per G at 5V supply.

So there is a much bigger voltage change = higher sensitivity for the 2G unit.
 
M

MartinM57

Moderator
I've used the Dimension Engineering device - very easy to use and very accurate.

...there's a very long post here somewhere about trying to make it more accurate using CALIBADC10, where (my) conclusion was that CALIBADC10 made things significantly worse and should be avoided almost completely (in fact I don't think I will ever use it again)
 
J

JaniM

Member
Ok, now I understand.
The idea is to keep car in balance automatically. Measuring pressure and angle.
So speed, acceleration and cornering effects to calculations?
 
D

Dippy

Moderator
I'm being very thick today. But, how can you get reliable tilt readings from an accelerometer in a dynamic vehicle?
 
B

BCJKiwi

Senior Member
OK we need more information.
I had not worked out from your description that the purpose was to level a vehicle while it was driving down the road - if, indeed, that's what you intend.

An accelerometer measures G forces. Every bump, acceleration/deceleration, cornering force etc will generate fluctuating readings.

An accelerometer would only be of value for leveling in a relatively static or slowly changing environment - like setting up the pressures to attain a level system.

So, please explain.

Having said that, and having used an accelerometer in a car, whilst there is rapid change, with vibration and bumps being detected, these are normally 'damped' by software, to achieve usable results. The mounting is also important and is sufficiently flexible to damp chassis vibration.

However, how fast the readings need to be, how much damping you want, or can tolerate, all depends on the application.
 
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J

JaniM

Member
That is what I'm wondering??
The cars acceleration must be shut out from calculation.
That why measuring distance from body to ground, would be better.
Each corner/axle should have some level sensor. One solution is potentiometer, but I'm looking some "wireless" solution, like sonar.
It have to be reliable, in rain, dust. Mechanical level indicator is.

This is the original idea:
http://www.x-eng.co.uk/Sproklegrommet/LRSuspension/Index.asp

So do I need inclinometer at all? I don't drive off road, sometimes strip, cornering and daily drive.

But ask more, I'll try explain with my english :eek:
 
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