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Introduction to DC motor Tachometer - Experiment 4 | EMCH 367, Lab Reports of Mechanical Engineering

University of South Carolina (USC) - ColumbiaMechanical Engineering
Prof. V. Giurgiutiu

Material Type: Lab; Professor: Giurgiutiu; Class: MICROCNTROLLRS MECH ENGR; Subject: Mechanical Engineering; University: University of South Carolina - Columbia; Term: Fall 2009;

Typology: Lab Reports

Pre 2010

Uploaded on 10/01/2009

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EMCH 367 Fundamentals of Microcontrollers Lab 4
LAB 4 – DC MOTOR TACHOMETER
OBJECTIVE
The objectives of this laboratory are:
(a) To understand the functioning of a DC motor
(b) To test the DC motor tachometer program developed in Hmwk6.
PREREQUISITES
Floppy disk with the asm codes for the program:
LASTNAME_Firstname_RPM.asm
Hard copy (printout) of Hmwk6 – Digital tachometer. When printing, use the 'pages per sheet'
option in the lower right corner of the print dialog-box with settings of 4 or 2 (depending on your
eyesight) to save paper. You may want to experiment a little with this before printing the full
document.
PROCEDURE
The students will utilize the asm code developed with the THRSim11 simulator for Hmwk6. The
students will go through the printout of Hmwk6 step by step and will verify that the MCU responds to
instructions as expected.
The lab is divided into sections. After completing each section, the student will ask the TA to check the
student’s work and make a check mark on that section.
The asm code is activated into the MCU following the standard procedure learned in Lab 1.
EXPERIMENTAL SETUP
The experimental setup for this experiment consists of a DC electric motor, a speed-control
potentiometer and its electronics, an emitter-detector sensor, a disk with an aperture (hole) attached to
the DC motor shaft, and a pair of 7-LED displays connected through appropriate electronics to a 8-pin
Port B connector. The aperture in the disk spins through the infrared emitter-detector sensor. The
emitter-detector sensor sends a High (5V) signal when the aperture in the disk allows the beam of light
to pass through. The emitter-detector sensor output wire is attached to the input capture pin IC1 on Port
A.
The speed of the motor is controlled by a potentiometer and an electronic timer circuit. The
potentiometer is a variable resistor. By varying the angular position of the potentiometer (turning the
knob), one varies the timer’s capacitor’s charge and discharge path resistance, which, in turn, varies
the duty cycle supplied to the DC motor. As the duty cycle to the DC motor is varied, the power
delivered and speed also vary.
Dr. Victor Giurgiutiu Page 1 11/28/2020
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Download Introduction to DC motor Tachometer - Experiment 4 | EMCH 367 and more Lab Reports Mechanical Engineering in PDF only on Docsity!

LAB 4 – DC MOTOR TACHOMETER

OBJECTIVE

The objectives of this laboratory are: (a) To understand the functioning of a DC motor (b) To test the DC motor tachometer program developed in Hmwk6.

PREREQUISITES

Floppy disk with the asm codes for the program:  LASTNAME_Firstname_RPM.asm Hard copy (printout) of Hmwk6 – Digital tachometer. When printing, use the 'pages per sheet' option in the lower right corner of the print dialog-box with settings of 4 or 2 (depending on your eyesight) to save paper. You may want to experiment a little with this before printing the full document.

PROCEDURE

The students will utilize the asm code developed with the THRSim11 simulator for Hmwk6. The students will go through the printout of Hmwk6 step by step and will verify that the MCU responds to instructions as expected. The lab is divided into sections. After completing each section, the student will ask the TA to check the student’s work and make a check mark on that section. The asm code is activated into the MCU following the standard procedure learned in Lab 1.

EXPERIMENTAL SETUP

The experimental setup for this experiment consists of a DC electric motor, a speed-control potentiometer and its electronics, an emitter-detector sensor, a disk with an aperture (hole) attached to the DC motor shaft, and a pair of 7-LED displays connected through appropriate electronics to a 8-pin Port B connector. The aperture in the disk spins through the infrared emitter-detector sensor. The emitter-detector sensor sends a High (5V) signal when the aperture in the disk allows the beam of light to pass through. The emitter-detector sensor output wire is attached to the input capture pin IC1 on Port A. The speed of the motor is controlled by a potentiometer and an electronic timer circuit. The potentiometer is a variable resistor. By varying the angular position of the potentiometer (turning the knob), one varies the timer’s capacitor’s charge and discharge path resistance, which, in turn, varies the duty cycle supplied to the DC motor. As the duty cycle to the DC motor is varied, the power delivered and speed also vary.

WIRING DIAGRAM

Wire Connection Red wire +5 V Black wire 0 V (Ground) Yellow wire Signal wire to input capture pin IC Figure 1 DC Motor tachometer experiment to which the present software example is relevant.

CIRCUIT DIAGRAM

Transmissive Photomicrosensor (Emitter/Detector) MOSFET DC Motor Speed-Controlling Potentiometer 555 Timer 7-Segment Display Port B Connection Lamp Test

Table 1 Speed description Voltage (V) Period of rotation,  (ms) Rotation speed,  (rad/s)

RPM

Motor constant, K Full-speed ¾-speed ½-speed ¼-speed Very slow Stopped

PART II – DC MOTOR TACHOMETER (70%)

The program LASTNAME_Firstname_RPM.asm developed in Hmwk6 will be used to measure and display the rotation speed using the microcontroller input capture function IC1. Recall from Hmwk6 that T1 is the first time when a falling edge transition is encountered on pin IC1, while T2 is the second time when a falling edge transition is encountered on the same pin IC1. This corresponds to the time between two consecutive passages trough the emitter-detector sensor of the hole in the rotating disk. The difference between T2 and T1, plus the time taken by the overflows, will represent the period of rotation of the disk. Hence, one can calculate the rotation speed and display it. Since the experimental setup has only two 7-LED displays, the rotation speed will be displayed in 100s RPM.

  1. Activate the program LASTNAME_Firstname_RPM.asm and let it run TA checkmark ________
  2. Read the displayed rotational speed and enter the values in the table.
  3. Calculate the error between the displayed value and the calculated value rotation speed value. In this calculation, take the rotation speed resulting from oscilloscope measurements as the standard.
  4. Calculate the average motor constant and enter its value in the table. TA checkmark ________
  5. Repeat for the other voltage settings. TA checkmark ________ Average motor constant, Kav

Table 2 Speed description Voltage (V) Period of rotation,

(ms) Measured speed (RPM) Displayed speed (x100 RPM) Error in rotation speed measurement (%) Full-speed ¾-speed ½-speed ¼-speed Very slow Stopped