Electronic Instrumentation: Project 2 Information

Spring 1998

Goal: Using given design of an optical transmitter/receiver, design, build and test an optical link for the seismometer built in Project 1. Either the output from the coil or the amplified strain gauge can be used as the source.

Group Responsibilities
• Both the receiver group (R) and the transmitter group (T) will provide significant content for the pre-project and final reports. It is up to the individual groups to decide whether they would prefer to write one report for all four students or to separately address the receiver and the transmitter.
• Both groups will build the circuits as they are shown on the posted diagrams. There are a few open component choices in the diagrams, but we will have only a limited number of components available. That should not deter anyone from thinking about how to improve the circuits. If possible, different components will be obtained over Spring Break. If not possible, additional points will be given for improved designs.
• T will investigate an audio source for their transmitter: a portable tape player or CD player (connect to the earphone jack). If one of the computers at your station has a CD player, you can also use that. Output voltage levels for the source should be measured early on to see if the transmitter circuit will have sufficient signal to drive it. Voltage levels at all points of the tranmitter circuit must be measured and documented. A comparison must then be made with the voltage levels and frequencies produced by the cantilever beam. Any changes in the circuit design should be identified. The seismometer signal might be too large, for example.
• Both groups should consider methods to improve transmission and reception of the optical signal by, for example, blocking unwanted light.
• R will study their circuit both as an optical receiver and an audio amplifier. Voltage levels at all points in the circuit must be measured and documented. These measurements will be made with two loads: a speaker and a resistor with the same value as the speaker.
• T will determine the Thevenin equivalent source representation for the walkman and the seismometer. R will determine the equivalent Thevenin source representation for the phototransistor.
• For each measurement made, there should be some discussion regarding which features of the data make some sense and which do not.
• Something to think about for each circuit: Since it is required to look at each circuit with different sources and the receiver with different loads, it should be possible to determine the input impedance of the transmitter and the output impedance of the receiver.
• Each group should find some information that relates to their circuit on the web and the URL included in the report.
• Finally, any questions on whether or not some task should be part of the project should be sent to one of the course staff. Questions and answers will be appended to this list.
• Pre-Project Report: Your pre-project report must address the questions and issues listed in the syllabus and should include most of the following information or address most of the following questions/issues:
  1. Include a diagram of the circuit(s) you are going to build. That is, a diagram of the receiver or transmitter and the appropriate variations for different sources or loads.
  2. Discuss the operation of the circuit
  3. Discuss the operation of the ICs (integrated circuits) in your circuit.
  4. What function do the components perform?
  5. Over what frequency range will your circuit work? Does the range include both audio frequencies and the frequencies of the cantilever beam?
  6. How is the audio information transmitted throughout the circuits (from the tape player to the speaker)?
  7. What types of signal might you input into your circuit?
  8. Describe your input and output signals (e.g. units).
  9. How might you simulate your circuit on PSPICE? What components might you have to approximate?
  10. How will you test your circuit? Write up a simple procedure that you will follow.
  11. What parameters might you use to quantify the fidelity of your setup?
  12. What variables/factors do you expect to affect the operation of your circuit?
  13. What changes in the circuit design would you suggest that could improve its performance?
  14. What kind of noise might you expect to find and how might you minimize it?
  15. List the name of your partner and the names of the partners in the other group you are working with.
  16. Provide some useful information about your circuit or integrated circuit that you found on the WWW. A good idea would be to look for a circuit that seems to be similar in design if not similar in purpose.
  17. Include some information on the properties of typical small speakers. How does a speaker work? What drives it? Why can it be used as a microphone? What is their nominal impedance, power rating, inductance, capacitance or whatever else you can find out.
  18. Develop a simple design for improving the transmission of the LED or reception of the photo-transistor.