UCLA IEEE NATCAR 2004 SUMMER CLASS Magnetic Sensors & Power Regulation

Introduction Wilson Chen Internal Vice President IEEE NATCAR member 03 Sensor Circuit P.I.D Algorithm Power Management

Magnetic Field and Coil What does a 75kHz, 100mA rms AC current mean? Magnetic Field around a wire (1/r 2 ) Brief review of inductor V = L (di / dt)

Different Orientation of Inductor Horizontally above the wire Advantage Provide continuous band of reading Disadvantage Relatively short range Can sacrifice reading amplitude for range

Cont. Vertically above the wire Advantage Very long range of detection Disadvantage 0 reading when on directly on top of the wire Must program with caution

Comparison between Optical Sensor and Magnetic Sensor Magnetic sensor provides a relatively long range of analog reading while optical sensor only provides discrete reading of 1 or 0. Magnetic sensor is very sensitive to noise. The signal obtained thus is not often clean; Optical sensor outputs a clean signal of 1s and 0s.

Building a Magnetic Sensor Circuit Different Stages

LC Tank LC tank, which is an energy storage device, is our sensing unit. Resonance Frequency ω r = √(1/(LC)) Theoretical value vs. practical value

Filters Review of bandpass filters Center Frequency, Cut-off Frequencies Minimize bandwidth Types of bandpass filters RC lowpass and RC high pass Active bandpass filter

Filters RC lowpass cascaded with RC highpass filter

Designing a Filter It’s very crucial to set the center frequency at 75kHz Make sure gain is closed to 1 Determine cut-off frequencies Low end: 60Hz (surrounding noise) High end: 400kHz (AM radio) Design Techniques Calculate theoretical values Use PSpice to run simulations with different values. Use the simulation results.

Filter Yes, after all these talks, filter is only an optional component in this particular sensor circuit. =(

Amplifier Circuit Amplifier circuit is the most important part of our sensor circuit design. What does an amplifier do and how does it work? Choosing an amplifier circuit Simple and straight forward Can precisely adjust the gain easily Don’t use any inverting amplifier

Building an Amplifier Circuit Choose the right type of OPAMP chip Use Qua-OPAMP Voltage operational range (+/- 5V) Frequency operational range Notice that you will only have VCC+ Use potentiometer to set amplifier gain Make sure your gain is not large enough to saturate the OPAMP when the sensor is directly on top of the wire

Amplifier Cont. Don’t use this! This is an inverting amplifier.

Rectifier Review of diode What is a rectifier Full wave rectifier Half wave rectifier

Building a rectifier Realize there is a 0.7v drop across the diode Choose the RC value carefully RC should be much greater than 1/f However, if RC is too big, the response of the sensor circuit output would be slow.

Complete Sensor Circuit

Input and Output

Sensor Systems The more sensors you have, the more information we can obtain about the current position of your car. Prepare for at least 5 sensor circuits Design the range of your sensors It’s not necessary to be good to have too long of a range Again, lifting sensors will give u a longer range

How do we orient sensors The most basic configuration Left, right and center Self correction P.I.D. ready Sufficient enough to handle most of the track Advance configuration More side sensors to handle special cases Front sensors to detect curve

Dealing with sensors Sensor reading plot is EXTREMELY important!!!

Dealing with sensors Discover a lot of small, but every important behaviors of your sensors Reading is a exponential function Manipulate all the readings and generate a linear output

Dealing with noises Noises from power source Filters Ground noises Filters? Avoid ground loops as much as possible PCB Ground Strap

Other Tips Use twisted wire for sensors Stabilize sensors as much as possible Tape? Glue? Use terminal blocks only for power connections; For sensors, use connection pins.

Power Regulation Why do we need power regulation? Device the needs to be regulated Servo Sensor Circuit Motor?? Types of regulator Switching Regulator (bad guy for us!!) Possibly reduce power consumption Linear Voltage Regulator Low drop-out

The End