OBJECTIVES

Use an NXT to control the speed of a DC fan motor. You will us a potentiometer to set the speed and the second fan motor as feedback. Use the circuit from Lab 1 to control the output voltage level of a LM317 variable voltage regulator. This will require writing an interfacing program in NXT-G that will utilize the outputs and inputs for the prototype board and building breadboard circuits to interface. Refer to "HiTechnic Experimenter's Kit Handbook" by HiTechnic.

EQUIPMENT

1ea = NXT brick 1 ea = HiTech NXT prototype board 1 ea = R/2R ladder network

1 ea = breadboard with wire jumpers 1 ea = 411 Op Amp 2 ea = DC fan motors

1 ea = LM317

PROCEDURE

Part 1: Motor Speed Control

Use a potentiometer to set the speed of a fan motor.

1. The potentiometer will control the digital output of the NXT.

2. The circuit from Lab1 will control the output voltage level of a LM317.

3. The output of the LM317 will power a DC computer fan.

4. The potentiometer input and the output to the control circuit are to be displayed on the NXT's LCD.

5. Record the following values:

Min. Input Voltage: ____________ Max. Input Voltage: _____________

Min. Output Voltage: ___________ Max. Output Voltage: ____________

6. Demonstrate the circuits operation.

Part 2: Provide Feedback to control loading.

1. Mount the two fans together so that the first fan spans the second.

2. Use the output of the second fan as feedback to adjust the control voltage.

3. The potentiometer input, feedback input and the output to the control circuit are to be displayed on the NXT's LCD.

4. Record the following values:

Min. Feedback Voltage: ___________ Max. Feedback Voltage: ____________

5. Demonstrate the circuits operation by loading the output.

The written report will include the following:

a. A description of how the system is to work.

b. A description of the system's operational programs.

c. A copy of both the NXT-G programs used with programming annotations.