ELEC 332

In the Lab

Since all of this week's hardware has already been built for you, there's not very much to do in the formal lab portion of this week's exercise. Our main goal here is to verify that everything works as it is supposed to, then move on to the centerpiece of this week's exercise, the design challenge.

Our new components this week include two new modules and an accessory. Since a radio system requires both a transmitter and a receiver, we have at least two copies of each.

Radio Board.: This can function as either a transmitter or receiver, depending on its program, and is described at length in the Background section.
(Click to enlarge)
5-Pin SMB Feedthru.: This serves the same purpose as the 10-pin breakout board used in previous exercises, but it works with the 2-signal, 5-pin connector (e.g. J4 on the MSP430 module).
(Click to enlarge)
915 MHz Antenna.: Due to its construction, this type of antenna is often referred to as a rubber ducky antenna.
(Click to enlarge)

Part 1: Transmitting Arbitrary Binary Signals

The easiest way to use our radio chip is as a direct FSK modulator/demodulator. I.e. we put a binary signal into the transmitter and the same signal comes out of the receiver. We could use this to transmit digital data, e.g. by using the SIO data stream from Exercise 3. Or we could transmit PWM encoded analog data such as the motor control signal from Exercise 4. Or we could transmit timing information such as the sonar pulse from Exercise 6. Or we could just send a square wave from the function generator.

Assemble the modules.
Since the main point of wireless communication is to transmit information between two widely separated points, we will eventually want to put the transmitter on one breadboard and the receiver on the other. However, initial program download and checkout is easier with both the transmitter and receiver modules on the same bench. The easiest way to achieve this is to put the transmitter in one corner and the receiver in the other corner of the same breadboard.
Connect one of the antennas to the SMA connector on the transmitter.

(Click to enlarge) On both the transmitter and receiver, connect one of the 5-pin SMB feedthrus to the 5-pin connecter on the right side of the top edge of the radio module (J4).
(Click to enlarge) If you are placing both the transmitter and receiver on the same breadboard, don't put an antenna on the receiver (to avoid overload).
(Click to enlarge)
Connect a 10x probe to channel 1 of the scope. Connect J4-4 of the receiver (the left hand SMB connector) to channel 2.

Set up the spectrum analyzer and function generator.
With the help of a SMB to BNC adapter, install one of the antennas on the input of the spectrum analyzer.
(Click to enlarge) Set the center frequency to 915 MHz, the span to 500 kHz, and the reference level to 0 dBm.
Set up the function generator to produce a 1 kHz square wave. Adjust the amplitude and offset so that the low value is 0 V and the high value is 3.3 V. Using one of the 5-pin SMB feedthru modules, connect this signal to J4-4 on the transmitter module (second pin from the left on the top right connector).

Build, load, and run the transmitter program.
With the debugging interface connected to the transmitter module, compile, load, and run the program fsk_xmit.c from this week's zip file. The green LED on the CPU board should come on. You should be able to see the transmitted signal on the spectrum analyzer. If necessary, adjust the spectrum analyzer for a satisfactory display. Change the frequency of the square wave and observe how the spectrum changes.

Build, load, and run the receiver program.
Move the debug interface to the receiver module. Compile, load, and run the program fsk_recv.c. You should be able to see the received signal on channel 2 of the scope. What is the maximum frequency square wave that can be reliably transmitted?

Part 2: Packet Transmission

If we want to send data, rather than timing information, the radio chip includes hardware to simplify and speed up that task. Rather than an asynchronous protocol like we used in Exercise 3, it uses a synchronous protocol with the data assembled into packets. Although the packets can be of any size, our example code transmits just a single data character per packet. Additional bits are required for bit and word synchronization.

Assemble the modules.
On the transmitter, move the 5-pin SMB feedthru from J4 to J3.
(Click to enlarge) Connect the lower SMB connector (J3-4) to the external trigger input of the scope. Leave the receiver connected as in the previous part, with J4-4 connected to channel 2 of the scope.
(Click to enlarge)

Build, load, and run the transmitter program.
Move the debug interface back to the transmitter module. Compile, load, and run the program pkt_xmit.c. This program will transmit a single byte packet with the value of the byte increasing by one with each transmission. For now, do not reprogram the receiver.
Adjust the scope for a stable trigger from the external input. Adjust the timebase to display a single received packet on channel 2. You should be able to identify the preamble, sync word, data byte, and trailer of the packet.

Build, load, and run the receiver program.
With the receiver in packet mode, we can no longer view the raw FSK received signal. Instead, a single pulse per received frame will appear on the pin connected to channel 2. You can either leave this connected and use channel 1 to monitor the more interesting receiver output, or you can move the SMB feedthru to J3.
(Click to enlarge) Move the debug interface to the receiver module. Compile, load, and run the program pkt_recv.c. The signal on J3-4 should be a square wave whose period is proportional to the value of the byte in the packet from the transmitter.


Assemble the modules.		Since the main point of wireless communication is to transmit information between two widely separated points, we will eventually want to put the transmitter on one breadboard and the receiver on the other. However, initial program download and checkout is easier with both the transmitter and receiver modules on the same bench. The easiest way to achieve this is to put the transmitter in one corner and the receiver in the other corner of the same breadboard. Connect one of the antennas to the SMA connector on the transmitter. (Click to enlarge) On both the transmitter and receiver, connect one of the 5-pin SMB feedthrus to the 5-pin connecter on the right side of the top edge of the radio module (J4). (Click to enlarge) If you are placing both the transmitter and receiver on the same breadboard, don't put an antenna on the receiver (to avoid overload). (Click to enlarge) Connect a 10x probe to channel 1 of the scope. Connect J4-4 of the receiver (the left hand SMB connector) to channel 2.
Set up the spectrum analyzer and function generator.		With the help of a SMB to BNC adapter, install one of the antennas on the input of the spectrum analyzer. (Click to enlarge) Set the center frequency to 915 MHz, the span to 500 kHz, and the reference level to 0 dBm. Set up the function generator to produce a 1 kHz square wave. Adjust the amplitude and offset so that the low value is 0 V and the high value is 3.3 V. Using one of the 5-pin SMB feedthru modules, connect this signal to J4-4 on the transmitter module (second pin from the left on the top right connector).
Build, load, and run the transmitter program.		With the debugging interface connected to the transmitter module, compile, load, and run the program fsk_xmit.c from this week's zip file. The green LED on the CPU board should come on. You should be able to see the transmitted signal on the spectrum analyzer. If necessary, adjust the spectrum analyzer for a satisfactory display. Change the frequency of the square wave and observe how the spectrum changes.
Build, load, and run the receiver program.		Move the debug interface to the receiver module. Compile, load, and run the program fsk_recv.c. You should be able to see the received signal on channel 2 of the scope. What is the maximum frequency square wave that can be reliably transmitted?


Assemble the modules.		On the transmitter, move the 5-pin SMB feedthru from J4 to J3. (Click to enlarge) Connect the lower SMB connector (J3-4) to the external trigger input of the scope. Leave the receiver connected as in the previous part, with J4-4 connected to channel 2 of the scope. (Click to enlarge)
Build, load, and run the transmitter program.		Move the debug interface back to the transmitter module. Compile, load, and run the program pkt_xmit.c. This program will transmit a single byte packet with the value of the byte increasing by one with each transmission. For now, do not reprogram the receiver. Adjust the scope for a stable trigger from the external input. Adjust the timebase to display a single received packet on channel 2. You should be able to identify the preamble, sync word, data byte, and trailer of the packet.
Build, load, and run the receiver program.		With the receiver in packet mode, we can no longer view the raw FSK received signal. Instead, a single pulse per received frame will appear on the pin connected to channel 2. You can either leave this connected and use channel 1 to monitor the more interesting receiver output, or you can move the SMB feedthru to J3. (Click to enlarge) Move the debug interface to the receiver module. Compile, load, and run the program pkt_recv.c. The signal on J3-4 should be a square wave whose period is proportional to the value of the byte in the packet from the transmitter.