2007 rew sensors_allegro

September 2005 Allegro Confidential

FIRST Presentation January 2007

Allegro’s ATS642 Hall Effect SensorAllegro’s ATS642 Hall Effect Sensor “A great way to measure the speed and position of a “A great way to measure the speed and position of a

rotating object”rotating object”

Michael DoogueMichael DoogueDirector of Strategic Marketing Director of Strategic Marketing

Allegro MicroSystems in Manchester, NHAllegro MicroSystems in Manchester, NH



What is a Hall Effect Sensor?What is a Hall Effect Sensor?• Hall effect sensors are silicon chips that

convert magnetic fields into electrical voltages– These sensors can be used to detect the

proximity of a magnet or a ferromagnetic object

– A ferromagnetic object is anything that a magnet will stick to!

• The Hall effect sensor provided to the FIRST teams is a special type of Hall effect sensor

• The sensor is used in anti-lock brake systems in automobiles to sense the speed, position and/or direction of a rotating gear

• Sensor output is a digital signal that is representative of the profile of the object passing in front of the sensor

• You can do a lot with this little sensor!

Hall Sensor



Automotive Applications for Allegro Hall Automotive Applications for Allegro Hall SensorsSensors

I told you that you could do a lot with Hall I told you that you could do a lot with Hall sensors!sensors!

Suspension SystemsPosition SensingChassis height

Electronic Power SteeringPosition Sensing

Motor CommutationCurrent Sensing

Safety Systems Airbag Diagnostics & Control

Occupant Sensing ABS/Traction - Wheel Speed Sensing

Convenience Systems Door lock Position Sensing

Window Position/Speed Sensing Window/Sunroof Direction

Sensing for anti-pinchSeating Systems

Various Contactless SwitchesMotor Controllers/Drivers

Wiper SystemsLCD screens

Powertrain ApplicationsCam/Crank SensorsTransmission Speed

SensorsThrottle Position Sensors

EGR Valve Position Sensors

Valve Position SensorsCurrent Sensing



ATS642: A Sensor and Magnet in a Single ATS642: A Sensor and Magnet in a Single PackagePackage

MAGNET

Element Hall IC

MAGNET

Low BHigh B

Grey denotes any material that a magnet will stick to



Getting Started: What is this thing?Getting Started: What is this thing?

8 mA

16 mAQuick review so that you understand what you are dealing with

when using this sensor!



ATS642: What Might You Do With It?ATS642: What Might You Do With It?• The device is an edge detector – the output is not analog

• If you have a rotating shaft on a motor:– If you use a gear with teeth in front of the sensor then the

sensor can also be used as a positional encoder that tellsyou when the shaft has rotated by a certain number of degrees

• The number of degrees between sensor output transitionsdepends on gear geometry and number of teeth on the gear

• Can also be used to measure the distance of travel for a wheelby counting the number of digital transitions for a uniform gear

– Motor rotation speed information can be detected by measuringthe time between output edges with a microprocessor or timer circuit

• Summary of applications:– Motor shaft or wheel speed/velocity measurement– Motor shaft or wheel distance measurement via counting of edges.

Gear at right has 60 teeth so 60 rising edge output transitions means that the gear has rotated one full revolution

– Can also use a “single tooth” ( maybe a screw) and obtain one output pulse per revolution

– Advanced users: direction of rotation sensing• Must use a gear with wide teeth and narrow valleys or vice versa• Requires precise timer circuit to detect duty cycle of output signal• Duty cycle is ratio of t1 and t2

t1t2



Getting Started: Applications CircuitGetting Started: Applications Circuit• There is a power pin and a ground pin for this electronic

device, but no output pin

• The digital output is actually the electrical current consumed by the device: 8 mA or 16 mA flowing into Vcc pin and out of GND pin

• A sense resistor and either an amplifier (comparator) or microprocessor can be used to measure the voltage across the sense resistor: for example VOUT(L) node at right

– Consult your mentors (or me, via e-mail) regarding comparator circuits that can be used to convert the current output of the ATS642 into a voltage (I am not sure what you guys have in your device kits)

– You may also use a low side resistor and a single microprocessor input to process the signal

• The voltage across the sense resistor is proportional to the current passing through the resistor (ohms law)

Voltage drop across resistor = 16 mA * RSENSE

• Be careful that the voltage drop across the device sense resistor does not reduce the voltage across the sensor to a level < 4 V across the sensor leads (or else the device will not operate)



DOs and DON’Ts When Using This SensorDOs and DON’Ts When Using This Sensor

Do Don’t• Be certain that the branded face of the

sensor faces the object to be sensed• Decrease the gap between the sensor

face and the object to be sensed as much as possible

• Make sure that a magnet (like the one in the 642!) will stick to the object to be sensed

• Use deep valleys between any teeth that you are trying to sense on a gear (shoot for at least 5 mm tall teeth)

• Align the sensor as shown in this drawing

• Feel free to e-mail me with questions at [email protected]

• Look at the ATS642 datasheet at http://www.allegromicro.com/datafile/0642.pdf

• Place the sensor more than 3 mm away from the object to be sensed (if possible)

• Allow the voltage across the sensor leads to fall below 4 V (be careful to size your sense resistor appropriately)

• Surround the sensor with ferromagnetic material that is closer to the sensor than the object to be sensed

• Rotate the device 90 degrees with respect to this drawing. If the leads of the device are in the same plane of a gear then the device will not work!



Good luck and Thank You for Your TimeGood luck and Thank You for Your Time

Come see me after this talk for a demo of a Come see me after this talk for a demo of a Hall sensor at work!Hall sensor at work!

Michael DoogueMichael DoogueDirector of Strategic MarketingDirector of Strategic Marketing

Allegro MicroSystems, Inc.Allegro MicroSystems, Inc.Manchester, NHManchester, NH

[email protected]@alum.dartmouth.org

2007 rew sensors_allegro

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