Cell Phone Controlled House Automation - Download as DOC by 6E7egKm


									                                                                            Keshav Bansal
                                                                                Tyler Rossi
                                                                              Daniel Hvala
                                                                           Project Proposal
                                                                               Feb. 7, 2007

                      Near-Field Communications
I.     Introduction

        Near Field Communication Technology or NFC is a short-range wireless
technology similar to the famous Bluetooth technology. It can be used for short range
transfer of information. As the demands for new and improved wireless communication
technologies are increasing, NFC provides unique advantages over other available
wireless technologies. In this project we will design a near-field transmitter and receiver
ands try to send data from one computer to another.

           Due to the rapid spatial decay of the field strength the system offers
              unique advantages of frequency reuse and less adjacent channel
              interference. Therefore, multiple devices in a small area can communicate
              with each other using the same transmitters and receivers.
           The receiver can be either active or passive. In passive mode it derives its
              operating power from the electromagnetic field generated by the
              transmitter. In this way the information can be sent to the places where it
              is hard to power the devices, such as within human body.


              The system will operate at a frequency of 13.56 MHz.
              The bit rate of up to 424 kbps is possible in this design.
              The operating distance can be up to 1 meter.
              No special software needs to be installed on either of the two computers to
               send data from one to the other.
              The same frequency can be used and tunable transmitters and receivers are
               not required.
              It can be used to implement any task that can be performed by Bluetooth.
II. Design:

              Figure 1.1 Block Diagram of Communication System


    MAX              VCO            Band Pass Filter   Power Amplifier

                    Figure 1.2 Block diagram of Transmitter

                                                     Band Pass Filter

          Amplifier   Band Pass Filter   Amplifier

                                                     Band Pass Filter


                      Figure 1.3 Block Diagram of Receiver
FSK Modulation and Demodulation:
Block Description

   1) Serial port connector: A female connecter is used to connect the receiver to the
      serial port of the connecter. Nine wire can be soldered to its 9 pins (all 9 pins may
      not be required) that connects the serial port to the MAX232A chip.

   2) MAX232A (receiver): It operates at 5V power supply. It receives the signal from
      the serial port and transforms its voltage level to TTL logic, i.e. it ideally
      transforms +30V to 0 V and -30V to 5V. It has internal charge pump ups and use
      external capacitors to do this conversion. Its output can be directly connected to a
      voltage controlled oscillator. It transmits data at the rate of 200kbps.

   3) Voltage Controlled Oscillator (VCO): It operates at a maximum supply voltage of
      15V. It output drifts in frequency for any drift in input. Its input which is coming
      from MAX232A will typically be either 0.5V or 3.4V. At this amplitude drift it
      drifts its frequency from 11MHz (space frequency) to 13.5MHz (mark frequency)
      at 25o Celsius. In this way it performs FSK modulation.

   4) Bandpass filter: This filter passes the mark and the space frequency produced by
      VCO but blocks all the harmonics of mark and space frequency that might also be
      produced by the VCO. We don’t want these harmonics to get amplified in next
      stage (by power amplifier) and get transmitted afterwards (by antenna).

   5) Power Amplifier: The bandpass filter normally attenuates the signal. Also, the
      signal strength in itself is not high enough to be transmitted. Therefore, a power
      amplifier must be used so that a signal with enough power can be transmitted.
      This operates at a maximum supply voltage of 12V. The gain is about 30 db for
      frequencies in the range of 10-20 MHz.
   6) Loop antenna: A loop of wire will be used as antenna. Its impedance can be
      measured using VNA. After a matching network can be designed for it so that
      they resonate near frequency of operation. Its impedance is mostly governed by
      its inductance L which is given by:
      L = µ a [ln (16a/d) – 2]
      µ = permeability of free space.
      a = area of the loop
      d = wire diameter


   1) Loop Antenna: This antenna will be very similar to the transmitter antenna. Its
      impedance can be measured using a voltage network analyzer (VNA). Eventually
      a matching network can be designed for it so that they resonate near the frequency
      of operation.

   2) Low Noise Amplifier (I): Placed at the input of the receiver. It can be powered
      from a 5V power supply. It has a unity gain bandwidth of 50MHz. From 15MHz
      to 17MHz it has a gain of approximately 8dB. Since this amplifier amplifies
      signals below and above the desired signals, a bandpass filter centered around the
      desired signal must follow the amplifier to isolate the desired signal.

   3) Bandpass Filter: We only require processing the signals transmitted by the
      receiver. However, the antenna catches all the signals that get amplified by the
      amplifier. The bandpass filter removes unwanted signals and also prevents
      The bandpass filter implements an operational amplifier and the design is derived
      from a Texas Instruments publication available at
      Pertinent equations related to the design are:
      Q is the quality factor, or the center frequency (fo) divided by the bandwidth (BW)
      H is the internal gain
      The capacitance value was chosen to be 10nF
4) Amplifier(II): If the signal strength is still not enough more amplifiers can be used
   if necessary.

5) Mark filter: This filter is designed to catch signals that represent a digital 1. The
   filter is centered on mark frequency and has bandwidth smaller than the
   separation of Mark and Space frequencies. This way it passes the mark frequency
   through without much attenuation but greatly attenuates the space frequency. If 1
   was transmitted by the transmitter, its theoretical output is a signal at mark
   frequency. If 0 was transmitted, its theoretical out put is 0.

6) Space filter: It works same as mark filter but selects space frequency instead of
   mark frequency. If 0 was transmitted by the transmitter, its theoretical output is a
   signal at space frequency. If 1 was transmitted, its theoretical out put is 0.

7) Amplitude detector: The outputs of mark and space filter would be a time varying
   signal at certain frequency. To compare them we actually want to compare their
   magnitude. An amplitude detector can be used for the purpose. During the
   positive cycle of the output of the filter the diode in envelope detector conducts
   the signal and charge the capacitor is charged. When voltage goes negative, the
   diode is cutoff and the voltage output of envelope detector is still positive due to
   the discharging capacitor. The outputs of the two amplitude detectors become
   inputs to the voltage comparator.

8) Comparator: Can be powered from a +5V power supply. Its input voltages can
   range from -0.2V to 3.4V. It compares the output of the mark filter with the
   output of the space filter. It outputs a voltage of around 3.4 V if mark filter output
   is greater than space filter output (the digital signal transmitted was 1) and 0.4V if
   space filter output is greater than mark filter output (digital signal transmitted was
   0). This output can be directly connected to the appropriate input of MAX232A

9) MAX232 (Transmitter): It receives the signal from the comparator and
   transforms its voltage level to computer logic. It has internal charge pumps and
   uses external capacitors to do this conversion. It produces a +8V voltage to
   represent digital high and -8V voltage to represent digital low, which can be
   easily interpreted by computer as 1 and 0 respectively. Its data output is directly
   connected to the serial port data input.

10) Serial port connector: A female connecter is used to connect the receiver to the
    serial port of the connecter. Nine wires can be soldered to the 9 pins (all 9 pins
    may not be required) that connect the serial port to the MAX232A chip.
Performance Requirements:
   1) Transmission range of at least 1m.
      As the near-field communication is used in indoor environment, transmission
      range need not be very large. However, it must be at least 1m if we want to use it
      for a wide range of purposes.
      The receiver antenna should catch enough power from the transmitter antenna up
      to the distance of 1m. It this does not happen, power at the transmitter may be
      increased or the orientation of antennas may be varied.
   2) A bit rate of 212kbps will be aimed for. At this speed most of the actions
      performed with Bluetooth technology can be implemented. The bit rate also
      depends on the power transmitted by the transmitter.

III. Verification

Testing Procedure:
We will break the transmitter and receiver into sub modules.

Transmitter Testing:

   1) First the serial port will be connected to the MAX232A chip. We will try to send
      bits from the computer and see the output of the MAX232 receiver. Once we
      know the voltages it gives for digital 1 and 0, we will generate a square wave
      from a function generator with the same amplitude.
   2) The square wave will be input to the VCO and study the output. If the VCO
      doesn’t produce the required frequencies (12-14 MHz), we will try changing its
      supply voltage and input signal voltage level until its frequency drift is as required.
   3) The bandpass filter will be tested with signals from a function generator. It should
      pass the signals in the desired range and reject the unwanted frequencies. The
      value of its various components (R, L, C) will be varied to get the desired
      response. After that it will be connected to the VCO’s output.
   4) We will first use power amplifier to amplify a signal from function generator so
      see how it behaves. We will make sure that it is not driven into saturation. After
      that we will connect the bandpass filter’s output to its input and try to get the
      amplified input at its output. The two frequencies produced by the VCO should
      get amplified by similar amounts.
   5) The Antenna’s impedance will be determined using a vector network analyzer
      (VNA). A matching network will then be designed and tested to see if the parallel
      combination of loop antenna and the matching network resonates near the
      frequency of operation.
   6) Then a signal at the same frequency as the signal produced by VCO will be
      generated by a function generator. We will test the loop antenna with this signal.
      In testing we will make a similar loop antenna for the receiver and try to
      determine the relative orientation of the two antennas that results in maximum
      power transfer to the receiving antenna. The range of transmission will also be
      tested. This would be a good point to test the strength of the signal at particular
      distances to make sure that it falls within FCC regulations. If the signal strength is
      found to be more than allowed by FCC, we will try to generate the signal which
      falls under FCC regulations. After the amplitude of such a signal is known we
      will try to decrease the gain or power amplifier (by decreasing it supply voltage)
      or we will add an attenuation circuit to get the output within the allowable range.
   7) At this step the output of the power amplifier will be connected to the loop
      antenna. We will debug at this point if any components are not working. We
      should get same signal at the receiving antenna as the one we got while
      transmitting the signal from function generator.

Receiver Testing:

   1) All the filters will be tested separately. These filters include the bandpass filter,
      space filter, and mark filter. A function generator will test these filters with
      different frequencies. We will tune the filters so that they have required frequency
   2) The low noise amplifier will be tested in a similar manner as the power amplifier
      at the transmitter. The noise introduced by the amplifier will be studied. As our
      design is going to be mostly external noise limited, we may not have to worry a
      lot about this. Once the LNA amplifies a signal at the same frequency as one
      received by the antenna, the antenna output will be connected to its input. The
      LNA should amplify this signal to a sufficiently high amplitude to be appropriate
      for further processing.
   3) Bandpass filter: This filter will be already tested with signals from function
      generator. LNA output will be passed through this filter. We will debug in case
      the desired signal gets attenuated and/or undesired signals are passed without
      sufficient attenuation.
   4) The output of the bandpass filter will be passed through the mark filter and the
      space filter. We should get expected outputs as the filters are already tested. In
      case of the desired signals being attenuated, we will tune the filters to change their
      center frequency and bandwidth.
   5) The amplitude detector will be first tested separately with the signals from a
      function generator. Once it is tuned to work at the mark and space frequency it
      will be applied to the output of mark and space filters.
   6) The voltage comparator will be first tested with square waves produced from two
      function generators. Its output should be either near 0 volts or near 4 volts. Once
      we know how it works, it will be used to compare the outputs of the two
      amplitude detectors. This output should be same as the digital data sent from the
   7) The output of the voltage comparator will be connected to the transmitter input of
      MAX232A (MAX232 has two transmitters and 2 receivers). The output of the
      transmitter will be connected to the data-in pin of the serial port via a serial port
     connector. We should see the voltage comparator output or the original signal sent
     from the transmitter computer. Any necessary debugging will be done.

  While testing various modules, their inputs and outputs will be displayed on an
  oscilloscope and a vector signal analyzer so we can analyze their characteristics. The
  oscilloscope will allow us to study their behavior in the time domain while the vector
  signal analyzer will allow us to study them in the frequency domain.

Tolerance Analysis:
  1) The design should meet the FCC regulations. The signal strength at 30m from the
     transmitter should be under the value allowed by the FCC. If our signal strength is
     too large we will decrease the current in the transmitter’s loop antenna.
  2) The oscillation frequency of the VCO is controlled by its supply voltage and
     temperature. It must not drift to the extent that the signals fall outside the
     passband of filters designed for them.
  3) There is a lower limit on the bandwidth for a filter at a certain center frequency.
     Bandwidth cannot be less that 1% of the center frequency. Due to this we may
     have to move the mark and space frequencies to some lower frequencies to get
     efficient channel selection.
  4) The relative orientation of loop antennas will affect the power absorbed by the
     receiver antenna. They must be first tested in various orientations to find the one
     that result in maximum power absorption by receiving antenna.
  5) Filters implemented with RLC circuits are not very efficient. Also, each R, L, and
     C component must be replacing with their respective models at the frequency of
  6) Amplifier saturation must be avoided.
  7) The response time of various components used must be small enough to make a
     transmission rate of 212kbps possible.
IV. Cost and Schedule

Cost Analysis


   ($50/hour)(150 hours)(3 people)(2.5) = $56,250

         Part                           Manufacturer    Cost    Quantity Total   Status
         MAX232A                        MAXIM           $5      4        $20     Obtained
         VCO (POS-25)                   MINI-           $17     1        $17     Ordered
         Power Amplifier (MAN-1)        MINI-           $19     1        $19     Ordered
         Amplifier (AD817)              Analog          $2      2        $4      Obtained
         Voltage Comparator             MAXIM           $6      1        $6      Ordered
         Passive Components              Parts   Shop   $0.10   100      $10     Obtained
         (capacitors, resistors, diodes,
         Serial Port Connecter           OOK            $3      4        $12     Obtained
         Circuit Boards                  PartsShop      $30     1        $30     Obtained
         Bread Board                    Parts Shop      $10     2        $20     Obtained
         Copper Wire                    OOK             $4      1        $4      Obtained
         Total:                                                          $142

Total Project Cost = $56,250 + $142 = $56,392

Keshav-VCO and Comparator
Dan-Computer Interface
Tyler-Filter and Amplifier

Task                                                     Target
Background research on system requirements               02/12/2007

All - P-Spice calculations for all individual modules     02/19/2007
and have the circuit diagrams mapped out and order all
the necessary components.
Build loop antennas
Test antenna range
Make sure design meets FCC regulations
Keshav – Test VCO with function generator                 02/26/2007
Tyler – Test Amplifiers
Dan – Test MAX232
Keshav- Test comparator                                   03/05/2007
Tyler – Build Filters
Dan – Send signal from computer and test with
Have working transmitter and debug                        03/12/2007
Try to synchronize the transmitter and the serial port of
the computer
Spring Break (work individually on modules)               03/19/2007

Have initial construction of transmitter and receiver    03/26/2007
completed and see how the system performs.
Mock-up Demos
Have transmitter and receiver working and see how the 04/02/2007
signal is modified during transmission.
Initial testing attempt to optimize operation parameters 04/09/2007
Test and troubleshoot bugs                               04/16/2007
Presentations                                            04/23/2007
Check out and final papers due                           04/30/2007

V. Schematics


                                           1                                       16
                                                    C1+     MAX232A        VCC

                                           2                                       15
                            0.1uF                   V+                     Gnd
    5                                      3                                       14
                      9                             C1-                  T1 Out
    4                                      4                                       13                        1           V      8                                                             1                      8
                      8                             C2+                   R1 In                                  VCC POSTune
                                                                                                                                                                                                  RF MAN-1RF
    3                                                                                                                 -25                                                                         In TransOut
                                   0.1uF   5                                       12                        2              7
                      7                             C2-                  R1 Out                                  RF
                                                                                                                     VCOGND                       In               Out                        2         Amp          7
                                                                                                                 Out                                                                              Gnd         Null
     2                                                                             11                                                                    BPF 1
                      6                    6        V-                    T1 In                              3                  6
                                                                                                                 GND   GND                                                                    3   Gnd     Gnd        6       VCC
    1                                      7                                       10                        4                  5
                           0.1uF                    T2 Out                 T2 In                                       GND                                                                    4                      5
                                                                                                                 GND                                                                              Gnd         DC
      Serial Port                          8                                       9
                                                    R2 In                R2 Out

   Antenna                                                                                                                                                          VCC

                                                                                                                         In           Out   Out
         1          AD817          8                                                                                             BPF 3                                      1     MAXBar 8
             Null        Null                                                                                                                                                      V+
                     Rec                                                            1        AD817       8
                     Amp                                                                Null      Null                                                                            913
         2                         7                                                          Rec                                                                           2     IN+
             -IN           +V
                                                                  Out               2         Amp        7                                                                        Volt Q
                                               In                                       -IN       +V                                                                              Com
         3   +IN          OUT      6                     BPF 2                                                                                                              3 IN-     Gnd 6
                                                                                   3    +IN      OUT     6
         4                         5                                                                                                                                        4      V-
              -V           Null                                                                                                                                                              LE
                                                                                   4                     5
                                                                                         -V       Null                   In                 Out
                                                                                                                                 BPF 4



                                                                                                                                             1                                      16                                   1
                                                                                                                                                       C1+     MAX232A     VCC
                                                                                                                                             2                                      15                                   2
                                                                                                                                                       V+                  Gnd
                                                                                                                              0.1uF                                                                       7
                                                                                                                                             3                                      14                                   3
                                                                                                                                                       C1-               T1 Out                           8
                                                                                                                                             4                                      13                                   4
                                                                                                                                                       C2+                R1 In
                                                                                                                                            5                                       12                                   5
                                                                                                                                                       C2-               R1 Out

                                                                                                                                             6                                      11
                                                                                                                                                       V-                 T1 In                           Serial Port
                                                                                                                        0.1uF                7                                      10
                                                                                                                                                       T2 Out              T2 In

                                                                                                                                             8                                          9
                                                                                                                                                       R2 In             R2 Out




  Vin                                              +


BPF3(Mark Filter):



  Vin                                              +

BPF4(Space Filter):



  Vin                                                     +


Amplitude Detector:
   Vin                                                                Vout

                                           C=75p               R=1k

To top