Re: Hall Effect Sensor.
 

Here are a few tips on the Hall Effect sensors:

These guys simply output a digital signal corresponding to whether or not a gear tooth is in front of them or not, and the polarity of the signal depends on the direction of gear rotation wrt the sensor itself (see the data sheet for more details: http://www.allegromicro.com/datafile/0660.pdf). Think of this device as a one-bit wheel encoder when you program for it.

The air gap, according to the manufacturer, should be 0.5-2.5mm, though they assure us that their adaptive sensing technology can make it work for an even bigger gap, especially with larger gear teeth.

The device has an open-drain output stage, but the digital inputs on the RC have pull-up resistors built-in, so you can directly connect the signal to the RC's inputs. Try to avoid grounding the signal wire, though, as this would technically be a short-circuit. Don't worry if you do -- the manufacturer says it has short-circuit protection on the output stage.

Re: Hall Effect Sensor.
 

We are given two Hall Effect Sensors. By using them to count teeth of sprockets on opposite sides of your robot you can calculate the difference in number of wheel rotations, and from that rotation of your robot.

If they are used this way, i believe, they work as a replacement for a gyro, although they would not account for being pushed or otherwise interfered with.

- Toby

Re: Hall Effect Sensor.
 

Guys,
Read some of the posts above before making guesses. The Hall effect sensors are easy tachometers that can tell you how fast a gear is rotating and how many gear teeth have passed by the front of it. Using two on the same gear, about 90% apart, can also give you direction information with some simple electronics or software interpretation. The accelerometer can be used only to give an indication of turning. It will give a large output for a bump or fast turn and a small output for a slow turn. Combine the data from all three and you will know that you have traveled "X" inches in some direction relative to your starting direction.
As a caveat, if your wheels are not firmly on the ground, counting gear teeth tell you nothing.

Re: Hall Effect Sensor.
 

Thanks, I haven't had a chance to re-check our kit yet, but I see that this is documented in the "Guidelines, Tips and Good Practices" document (page 26 - see attachment). IMO this should have been documented on the kit checklist (to look on the accelerometer). Seems these could be easily missed, even for those who know what they are looking for :o

Re: Hall Effect Sensor.
 

http://www.allegromicro.com/datafile/0660.pdf

I can confirm that is the proper spec sheet for the hall effect gear tooth sensor that is included in the 2005 FRC KOP. It is labled Data sheet 27627.107

Re: Hall Effect Sensor.
 

We thought we didn't have it either, but after reading that, we checked and found it, thanks

Re: Hall Effect Sensor.
 

Arghhh! I don't understand lol.

Ok the Hall Effect sensor counts teeth and has to be mounted very close to the gear.

The accelerometer measures acceleration. How is that done and where does it have to be mounted.

How do all these values come together in the RC and help me?

What does the code that we get for both these sensors do?

Re: Hall Effect Sensor.
 

If you know what your final gear ratio is (or you test to find out the correlation between counts and inches moved on the floor) you can determine how far the robot has moved. If it runs straight, you can tell where it is at any moment by keeping track of the counts. If you use the accelerometer, you can tell how much the robot has turned (or if it has turned the amount you want it to) so you now have direction and distance. Combine the two and get a rough idea where you are on the field. Be careful, the accelerometer output is proportional to the acceleration in one direction or the opposite direction. If it is mounted parallel to your direction of travel, it has no output. Read the spec sheet carefully to learn all of the nuances of the device and how to best filter out the info you need.

Re: Hall Effect Sensor.
 

So... They are sprocket-tooth encoders. Check.

How do we wire them? They have 4 pins, I haven't checked but it seems like they might fit on a PWM cable, but that only has 3 pins, so is it possible to wire it with only 3 pins or do we need to make new cables?

--Jonathan

Re: Hall Effect Sensor.
 

To wire this sensor, I suggest you check out the spec sheet that is linked numerous times in this thread. A link to the sheet is on the FIRST site at:
http://www2.usfirst.org/2005comp/Specs/gths1.pdf

For a basic overview, looking from the top of the sensor, the pins from left to right are supply, output, int. connection, and ground. it can take 4.5 to 24 volts input voltage (you would probably use 12), and the output will provide a digital signal whenever a gear tooth passes by (whether or not the output is high or low when a tooth goes by depends on the direction of rotation).

CHECK the spec sheet before you try it. It is helpful to see the diagram and check for yourself.

Scott

Re: Hall Effect Sensor.
 

Oops! You are right... With all the accelerometer discussion, I got all mixed up. The ADXRS sensors are nice, but you need to deal with the packaging. I think (not sure) the price limitations have been loosened enough that you can get an evaluation version of the accelerometer with some support circuitry brought out header pins that can be plugged into a board. This is much easier than dealing with a surface mount part, if you do decide to use it. Since there are more suppliers, it may also be possible to pick up other sensors now (the Memsic ones are also nice... and if it is allowed, you can buy it from Parallax pretty cheap.) Heh, you may even be able to get the old FIRST accelerometers from some supplier.

Re: Hall Effect Sensor.
 

How do you use the accelerometer to know how much you turned and in what direction?

What kind of value does it give out?

Re: Hall Effect Sensor.
 

Has anyone had any luck with mounting the hall effect sensors?

i haven't found anything that fits them.......

also, if you haven't read the manual it states that you must connect pin 4 to pin 3 externally.

-Leav

Re: Hall Effect Sensor.
 

Ok, someone help me, I'm not understanding how measuring the speed of the same gear twice would turn into a direction.

Re: Hall Effect Sensor.
 

Rich,

Please read http://www.chiefdelphi.com/forums/showthread.php?p=307123&highlight=encoders#post307 123.

We were talking about encoders on that page but the theory of quadrature remains the same as what Mr. S is talking about.