EE 451 - LAB 7

DTMF Detector

Part 2: Frequency Detector

Implement the detector discussed in Part 1 of Lab 6.

Choose a pin on Port B which you will use to indicate whether the frequency is present or not. Look at the schematic for the 56002 board (available in the lab) to determine how to connect to this pin. Using the EVM program, set up this pin as an output. Verify with a logic probe that you can change the state of this pin.

Write 56002 code to implement the detector. Put the output from your bandpass filter to one channel of your D/A, and the output from the detector to the other. Use your function generator to produce a sine wave of the correct frequency. Verify that the detector works properly.

Use a logic probe to verify that the selected output pin goes high when the selected frequency is present, and goes low when it is absent. For a 1 V P-P input signal, what are the lowest and highest frequencies which make the output pin go high? Compare this to your gain plot from last week's lab. to

Bill Rison