Sensors and Error Correction Codes

Question 1

What is the accelerometer?

Answer 1

An electromechanical device that measures acceleration.

• Static: Constant force of gravity by measuring amount of static acceleration due to gravity to find out the angle the device is tilted at with respect to earth
• Dynamic: Caused by movement of the accelerometer by sensing the amount of dynamic acceleration.

Question 2

What is capacitive accelerometer?

Answer 2

If there are two microstructures next to each other, they have a certain capacitance between them. If an accelerative force moves one of the structures, then the capacitance will change; adding some circuitry to convert from capacitance to voltage makes an accelerometer.

Question 3

What is MEMS Capacitive Accelerometer?

Answer 3

Micro-machined Electro-Mechanical Systems
C = e_re_o(A/d)
- Have two immovable plates between movable plates to detect smaller acceleration

Question 4

What are the common types of accelerometers?

Answer 4

• Capacitive
• Piezoelectric
• Piezoresistive
• Hall effect
• Magnetoresistive

Question 5

Accuracy cost comparison of the types of accelerometers.

Answer 5

Capacitive acceleration sensor has high accuracy and decently low cost.

Question 6

What is a Gyroscope?

Answer 6

It measures rotational velocity in 3 dimensions: pitch, roll, yaw
- Gyroscope and accelerometer provides 6 degree of freedom motion tracking system

Question 7

What is a vibrating structure gyroscope?

Answer 7

Coriolis force is proportional to both angular velocity of rotating object and velocity of the object moving towards or away from the axis of rotation.
Coriolis force is felt by the object along the y-axis.

Question 8

What is the magnetometer/compass?

Answer 8

Measures the strength of earth’s magnetic field and vector points towards the magnetic center of earth - uses hall effect

Question 9

What is sensor fusion for motion detection?

Answer 9

• Primarily uses Enhanced Kalman filter

- Relies on input from multiple sensors for better sensor calibration, noise compensation, etc.

Question 10

What are the two types of infrared sensors?

Answer 10

Proximity sensors and ranging sensors.

Question 11

What is proximity sensors?

Answer 11

Can only detect when an object is within a predetermined range.

Question 12

What is ranging sensors?

Answer 12

• Provide an analog output or a multiple bit output
• Ranging sensors can determine the actual distance of an object from the sensors
• The triangulation technique uses focused beam emitter and separate receiver array to measure angle.

Question 13

What are the applications of error correction codes?

Answer 13

• Storage
• Wireless
• Satellite and Space
• Digital Television
• High Speed Modems

Question 14

What are parity bits?

Answer 14

8th bit for parity
Even parity - make total number of 1 bits even
Odd parity - make total number of 1 bits odd
Use for error detection.

Question 15

What is cyclic redundancy check (CRC)?

Answer 15

• Data bits to be protected are treated as a binary number
• The binary number is divided by another pre-defined binary number
• The remainder is selected as CRC code
• Receiver checks if CRC matches
• Error detection only

Question 16

What is hamming code?

Answer 16

Error detection and correction

• One parity bit can tell us an error occurred
• Multiple parity bits can also tell where it occurred.

Question 17

What is hamming (7, 4)

Answer 17

7 bits total: 4 data bits and 3 parity bits
- Can find and correct 1 bit errors or
- find but not correct 2 bit errors
(Note: review how to calculate)

Question 18

What is the hamming code syndrome?

Answer 18

• If the syndrome is all zeros, there were no errors

- If there is a 1 bit somewhere, we know it represents an error

Question 19

What is the hamming code design?

Answer 19

• M bit word with detection/correction takes M=K bit words
• 2^k -1 >= M+K, we can detect, identify, and correct all signal bit errors.
  (See example)

Question 20

What are advanced error correction codes?

Answer 20

• Binary Convolutional Codes (BCC)
• Turbo codes
• Low Density Parity Check (LDPC) codes