ELEC 332

Design Challenge

Having successfully established a wireless communication capability, we could incorporate it into one of our existing projects or undertake a new project centered on wireless communication in its own right. To allow you to explore either path, there are two challenges this week, one from each category. As with our previous multi-challenge exercise, you need only accept one of them.

Some solutions to these challenges require more modules than a single group is likely to have. In particular, some require two MSP430 modules. If you choose one of these, you may undertake the challenge jointly with another group and pool your resources.

1. Radioteletype.
In previous exercises, we've sent data between the PC and MSP430 via the serial link. Each of these has been a one directional connection, with data either sent from the MSP430 to be displayed on the PC, or from the PC to control the process running on the MSP430. In many applications, data must be able to flow both ways. Rather than trying to build such an application on top of the data path, we'll just build the communication link and let two people talk to each other over it.

The challenge:
Assemble a system which allows bidirectional wireless text communication between two hyperterminal (or similar program) sessions. Since the radio modules are half-duplex, you will need to include a protocol for reversing the direction of transmission. One possibility: switch to transmit whenever a printing character is typed, switch to receive after a return is typed. If your battery power supply from Exercise 6 is working and you have a laptop with a serial port, you could make one or both of the nodes portable.

2. Active Sonar Distance Measurement.
In Exercise 7 we were able to determine the distance to an object by bouncing an ultrasonic pulse off it and measuring the round trip delay. This technique has the advantage of being able to measure the distance to any object, but has the disadvantage of never being certain what object has reflected the pulse. If we want to be able to measure the distance between two specific objects, we can place the transmitter on one and the receiver on the other and measure the one-way propagation delay. This requires the receiver to know when the transmitter pulse was launched, and since radio waves travel much faster than sound waves, we can use our wireless link to provide this information.

The challenge:
Assemble a system which measures the distance between two separate breadboards based on the propagation time of an acoustic signal from one to the other. You should display this distance in a meaningful way. Some possibilities:

  1. Convert to a character string and display on the PC, e.g. using hyperterminal.
  2. Convert to a frequency and display via the frequency measurement function of the oscilloscope.
  3. Convert to a voltage and display on a DMM.
If your battery power supply from Exercise 6 is working, you should make one of the two nodes portable.