Smart Appliance

1. Smart Appliance Matt Kerchenfaut Natalie DiIorio Aaron Cohen

2. Table of Contents • Smart Appliance Overview • Top Level View • The Power Circuit • The Communication Aspect

3. Smart Appliance Overview The goal of this project is to allow the appliances in a home to send basic information to a central control system. This will be attempted by using a signal with a center frequency of 100kHz, and using the existing power lines associated with the home to carry the information desired. Pertinent information to be tracked for an appliance is the voltage, current, and power at a given time. Also for an appliance such as a refrigerator the temperature could be monitored in order to let the appliance conserve power by reducing the temperature setting if temperature is too low, etc.

4. Advantages of PowerLine Communications • By using power-line communications the need for installing new communication networks is eliminated, thus reducing the cost of adding new technology to a home or system. • By reusing the existing power line wiring for data communication, installation time of the Smart Appliance is drastically reduced. • This product would allow the status of appliances to be determined, and therefore these can be monitored in order to optimize power consumption. • The Smart Appliance Communication Protocol would be beneficial to homes using alternate energy sources where power is limited and a key concern.

5. VOLTAGE SIGNALS LED DIP SWITCH MUX LED TEMP SENSOR LED DISPLAY RECEIVING END MICRO CONTROLLER SENDING END MICRO CONTROLLER INVERTER INVERTER COMPARATOR TWO INVERTERS TWO INVERTERS COMPARATOR OP AMP OP AMP Power Circuit Power Circuit BUFFER F I LTER BUFFER F I LTER WALL OUTLET WALL OUTLET

6. Input Signals Micro- Controller Control Lines Voltage • A variety of signals from an appliance can be sent to different inputs of the MUX. The MUX will choose the specific signal that needs to be read and send the corresponding signal to the microcontroller. Analog MUX LF13509 Temperature

7. Micro-Controller Protection Micro-Controller Protection • The input to each of the micro-controllers are protected by using TTL inverters to ensure that only 0V or +5V will be seen at the I/O ports. The output of the comparator is fed into an inverter to provide a clean TTL signal to the input of the micro-controller. To protect the output port of the micro-controller, two inverters were used to make a extra buffer that would isolate the port from the high voltage side of our circuit. Buffer Micro- Controller Comparator

8. Temperature Sensor • The LM335 temperature sensor allowed us to output a digital voltage level depending on the temperature. As the sensor was heated the voltage level decreased. • This was planned for two way communication in order to allow a signal to be sent to turn off an appliance when a threshold level was met (the appliance became too hot or cold).

9. Buffer circuit • This circuit will be the method we use to introduce our signal into the power line. • This buffer circuit is designed in order to use a large impedance to create a voltage drop which will allow the two signals with unequal voltages to be connected. • Therefore we will use a small capacitance of 1000pF in order to achieve a high impedance. Xc = 1/(ωC) which is approximately 1MΩ.

10. Filter • The focus of this circuit, which is located on the receiving end, is to pass our 125kHz signal in order to analyze the status of our appliance. • This circuit creates a large Xc impedance at 60Hz which we want in order to block the 60Hz signal in the power line. Also, the impedance at 125kHz will be effectively zero by using values which correspond to the resonant frequency.

11. Filter calculations • 1/sqrt(LC) = resonant frequency*2π • For our applications we want the impedances of the the inductor and capacitor to cancel at the resonant frequency so that the impedance seen by our signal is essentially zero. • At 60 Hz: Xc = 1/(ωC) = 2.6 MΩ • At 100kHz : Xc = 1/(ωC) = 1.6kΩ. Then by using the equation for the resonant frequency equation the corresponding inductance L =2.5mH. • Therefore the filter circuit creates a large Xc impedance at 60Hz which we want in order to block the power line signal. In addition, two additional capacitors were added to pass our high frequency signal and to further decrease the 60Hz component.

12. Op-Amp • An Op-Amp was used to amplify the signal to a value large enough for the comparator to read. • The LM747 (Dual LM741) Op-Amp was originally used, but the skew rate was too low for our needs. We replaced it with an LF356 Op-Amp. • The Op-Amp was used to make an inverting amplifier with a gain of about 25. Our input signal to the amplifier was about 1V p-p. The output signal was about 25 V p-p.

13. Op-Amp (continued) /\/\/\/\/\/ Filter Comparator LF356 /\/\/\/\/\/

14. Comparator • We used a comparator to convert our sinusoidal output waveform from the Op-Amp to a square wave output. If the voltage was above the DC voltage that it is being compared to, +5V will be outputted. If it is below the DC value, 0V will be outputted. • The DC offset was used to control the noise from the l20V line that might have gotten past the filter. The DC value was adjusted so that it was greater in magnitude than the noise in the line.

15. Comparator (continued) • Since the comparator will output zero for any value less than the DC value, the noise in the line will be canceled. • Noise in the line was only an issue when a zero signal was being sent. The noise in the line would make a noisy output. Vin Vout Vdc

16. Data Packet Format

17. Data Packet Format Explanation • Start Code: The 8 bit sequence that identifies the start of the data packet. • House Code: The 4 bit sequence that corresponds to the target’s House. • Appliance Code: The 4 bit sequence that identifies the Appliance the packet is intended for. • Data/Command: The 8 bit sequence that contains the command or other information about the appliance.

18. Actual Data Packet Encoding • Start Code: “1111 1110” • House Code: “0xxx” • Appliance Code: “0xxx” • Data/Command: “00xx xxxx”

19. Bit Encoding into Pulse Train

20. Data Rate Calculations

21. Testing: Error Rate • We took a sample of 12568 characters received by the micro controller. • Out of the received characters 273 characters were incorrect • Thus our error rate is:

22. The HC12 Implementation • Steps for Sending • Steps for Receiving • Sender Port Assignments • Receiver Port Assignments • Difficulties

23. Steps for Sending • First load the Data Packet into memory. • Second set the sending variables and flags. • Then, the ISR (Interrupt Service Routine) turns the PWM (Pulse Width Modulator) on or off corresponding to the number it reads from memory while counting the 8 cycles per bit being sent.

24. Steps for Receiving • First, find the Rising Edge of the input signal then set an Interrupt to occur 3 cycles later. • If no rising edge occurs for 3 cycles then determine bit and shift it into our input buffer. • Third, check the upper 8 bits of our input buffer for the start code. If the start code is found then we have read an entire data packet. • Fourth, execute appropriate actions for the data. In our case output to PORTB.

25. Sender Port Assignments • PORTAD7 = Voltage input from analog mux • PP0 = PWM Output to Buffer (TTL data signal) • PT0 = Output Compare (ISR turns PP0 pulse on or off)

26. Receiver Port Assignments • PORTB = Data Output to LEDs • PT6 = Input Capture from Filter (ISR) • PT5 = Output Compare 3 cycle delay timer (ISR)

27. Difficulties • The sending ISR has problems shutting off the Pulse Train after 4 pulses due to interrupts occurring faster than they are being serviced at 125KHz. This does not occur at 62.5KHz. • The program size for one way communication was nearing the memory limit with Debug loaded. • The clock skew between micro controllers was a difficulty overcome by triggering an interrupt on the rising edge. • We could not use the serial port as the stop bit was at a different frequency and could not be sent through our system.

28. Successes and Challenges • Originally we had problems dealing with the neutral, common, and ground connections. We came up with the conclusion to use only the “hot” line of the 120V line and the common of the power supply. Earth ground was eliminated because it caused distortion in our DC power supply. • Another challenge was attempting to eliminate as much 60Hz component from our signal in our filter. We used a resonant frequency and added additional high pass filters but small traces of 60Hz could still be observed in our signal. We were able to transmit a signal well enough to successfully complete our project.

29. Successes and Challenges • The attenuation experienced by our signal after going through the buffer, power line, and filter was significant. We had to account for this by using an op amp which had to be able to function correctly at high frequencies. We changed our original choice of the LM747 op amp to the LF356 op amp which worked as expected even when using high frequencies. • In addition, our original temperature sensor was not used because it was an obsolete part by motorola and data sheets were not accessible. Also the original choice for the temperature sensor required a current source which would add complication. The LM335 we chose eliminated these problems and worked successfully in our circuit.

30. Successes and Challenges • A major challenge was noise in the line. At times there were spikes experienced in the line possibly due to heat turning on, etc. A comparator was introduced to account for this.

31. Tolerance Analysis • We found that the system would work through about 25-30ft of line cord. It was difficult to test lengths of wire longer than this because most of the other outlets were on different circuit breakers. • The pulse widths of the output signal continue to decrease as the noise in the line increases. The minimum widths of the signals can be determined by the tolerance of the micro-controller.

32. Recommendations and Future Improvements • Add error correcting and parity. • Eliminate lost cycles when a 0 is sent. • Implement full 2 way communication. • Add detection if transmission line is in use. • Implement a GUI system to communicate with master HC12 for selecting input voltage to appliance HC12. • Use more frequencies to transmit data.