Electronics Design Laboratory Lecture # ECEN 7 Electronics Design Laboratory
Project Must rely on fully functional Lab circuits, Lab circuit is optional Can re do wireless or replace it with a different control method if desired. The project does not have to include remote control. Must include an additional hardware component. Programming only add ons or enhancements do not count. When selecting components check Range Voltage Communication ECEN 7 Electronics Design Laboratory
Sensors Range Ultrasonic Infrared Buttons Position Compass Accelerometer Gyros GPS Tilt Sound Voice Recognition Microphone Speakers Environment Temperature Humidity Altitude Pressure Light (LDR, etc) Physical Pressure Flex Vibration Buttons Other RFID ZigBee Bluetooth Other wireless Your robot Motors Actuators DC (Brushed or Brushless) Stepper Servo Linear Solenoid LEDs Single Color RGB w/ PWM control Infrared 7 segment Shields Motor/Stepper/Servo GPS Audio (wave, mp, etc) Ethernet GSM Wifi Larger controllers Arduino ECEN 7 Electronics Design Laboratory
Final Project and Experiment Final Project Project ideas and discussions this week, additional parts you may need? Parts can take. weeks to get here. Order early and order extras! Experiment Lab A: build the components of a wireless on/off and speed control circuit (should be done Tuesday this week) Lab B: prelab due on Thursday Write code for the Arduino to measure the on time of a digital input for speed control (should start this Thursday, finish Tuesday next week) Demonstrate wireless control of the robot, demo is Thursday next week ECEN 7 Electronics Design Laboratory
Data Wireless / /f m v tx RF /f c v rx Data Carrier frequency f c is fixed at MHz Modulation frequency f m is much lower By filtering v rx the sent data can be re created ECEN 7 Electronics Design Laboratory
Sinusoidal Modulation. -. - AM Modulation of RF signal at MHz Time Domain Carrier Modulation.. Frequency Domain ON/OFF Modulation (Amplitude Shift Keying (ASK). -. - /fm /fm /fm.. fm fm fm fc ECEN 8 Electronics Design Laboratory 6
Group A (Red Waveforms) wants to send a sec pulse starting at ms. Group A will use a f m = Hz modulation frequency Group B (Black Waveforms) wants to send a sec pulse as well, but starting at ms. Group B will use a f m = Hz modulation frequency Both groups are going to try and send this signal wirelessly, using a MHz wireless transmitter/receiver pair This is just an example of data sent by two groups...6.8...6.8 Group B Data Group A Data...6.8...6.8 ECEN 7 Electronics Design Laboratory 7
Both signals are modulated using a timer oscillating at Hz for Group A, and.khz for Group B VDC f m = Hz Group A Modulated Data Output...6.8...6.8 Group B Modulated Data...6.8...6.8 f m =.khz ECEN 7 Electronics Design Laboratory 8
The RF transmitter modulates the signal a second time at the carrier frequency of MHz - f m = Hz Group A RF - -...6.8...6.8 - - Group B RF f c = MHz -...6.8...6.8 f m =.khz ECEN 7 Electronics Design Laboratory 9
Both RF transmitters are sending on the same frequency In addition, there is a noticeable amount of noise in most environments The result is an extremely messy signal, and this is with just two groups transmitting simple data pulses. - Group A Transmission - Group B Transmission - RF Noise - - - - - - Total RF noise and signal Intesity -...6.8...6.8 ECEN 7 Electronics Design Laboratory
When neither transmitter is operating, the RF spectrum is dominated by noise This random noise floor is generally of a low magnitude and equally distributed across all frequencies Noise spectrum when no one is transmitting f c ECEN 7 Electronics Design Laboratory
When Group A begins to transmit, spikes in the frequency spectrum appear These spikes are much larger than the noise floor and at known frequencies! f c f m f c +f m f c ECEN 7 Electronics Design Laboratory
When Group B begins to transmit, additional spikes in the frequency spectrum appear These spikes are at a different frequency than Group A s transmissions! Neither signal overlaps with the other f c f m f c +f m f c ECEN 7 Electronics Design Laboratory
An RF receiver acts as a demodulator This demodulation shifts the frequency spectrum such that f c = MHz is shifted to Hz Both Group A and Group B receivers are picking up everything f m f m f c ECEN 7 Electronics Design Laboratory
Each group s filter is tuned to their specific modulation frequency This is how we separate our signal from noise and other groups nf R R nf VDC Group A ed Output R Group B ed Output 7kΩ VDC 7kΩ.μF f m f m ECEN 7 Electronics Design Laboratory
Each groups filter is tuned to their specific modulation frequency This is how we separate our signal from noise and other groups R R 7kΩ nf nf R VDC 7kΩ.μF VDC Magnitude...6.8...6.8 Group A ed Output Group B ed Output...6.8...6.8 ECEN 7 Electronics Design Laboratory 6
Each groups filter is tuned to their specific modulation frequency This is how we separate our signal from noise and other groups Magnitude...6.8...6.8 Group A ed Output f m Group B ed Output...6.8...6.8 ECEN 7 Electronics Design Laboratory 7
detector follows the peak value of the waveform This value is a diode drop less than the real peak! We can use a comparator on this peak detector output in order to generate our pulse outputs. In Out Magnitude......7V.7V V threshold V threshold.8.8.9.9..... ECEN 7 Electronics Design Laboratory 8
Complete R R nf R VDC v f v pd Comparator VDC V digital data to Arduino Output 7kΩ VDC V threshold VDC 7kΩ.μF R.μF R should have a gain of (db) at f m When you are transmitting, v f should be a V sinewave centered around. V RC time constant in the peak detector should be large enough so that ripple in v pd is small. The peak detector output v pd should be around V when you are transmitting. Comparator V threshold should be close to but below the (v pd ) min when you are transmitting ECEN 7 Electronics Design Laboratory 9
DATA is encoded via pulse width ton DATA You may use another (or another Arduino) on the transmitter side to generate the DATA signal ECEN 8 Electronics Design Laboratory