1. Microcontroller basics
Embedded systems for mortals

2. Transistors PWM Motors: Servo motor DC motor Stepper motor
Lesson 4
Transistors
PWM
Motors:
Servo motor
DC motor
Stepper motor

3. Transistor types Transistor = switching element,
Control a larger current with a smaller current (voltage)
Used as a switch, in amplifiers, logic, memory etc.
BJT (Bipolar junction transistor)
FET (Field-effect transistor)
Base, emitter, collector
Gate, drain, source
Cheaper, more noisy, lower switching speed, wastes current, robust,
More expensive, less noisy, higher switching speed, easily damaged if improperly connected
Low power applications
High power applications
Current controlled
Voltage controlled
Current limiting resistor
Pull-down (up) resistor
Darlington=two BJTs together
(e.g. TIP120)
MOSFET= Metal oxide semiconductor field effect transistor
JFET= Junction field effect transistor

4. Transistor types
BJT
FET

5. PNP and NPN P=positive, semiconductor doped to have ”holes”
N=negative, semiconductor doped to have electrons
NPN (N-channel)  connect the ground wire, when base/gate HIGH
PNP (P-channel)  connect the voltage source, when base/gate LOW

7. PWM (Pulse Width Modulation)
Basic terms
Duty cycle = Pulse Width / Wave Period

8. Duty cycle
100 %
75 %
50 %
←Ideal Square Wave
25 %
0 %

9. PWM Applications Servomotor angle control DC motor speed control
LED Dimming
Audio generation
Digitally generating analog voltages (requires filtering)

10. PWM with Uno Total of 6 pins with PWM capability (~ symbol)
PWM frequency
Pins 5 & 6: default: 980Hz ~1kHz
(62.5kHz base with 64 as prescaler)
Pins 3,9,10,11: default 490Hz ~0.5kHz
(31.25 kHz base with 64 as prescaler)
Can be adjusted (30Hz-62.5kHz) with setPwmFrequency();
CAUTION: Affects the delay() millis() and Servo functions

11. LED fading 220 ohm current limiting resistor!
File->Examples->Fading

12. DC motor
Can change speed according to voltage (voltage controlled with PWM)
Brushed and brushless
Requires an H-bridge for direction control (motor drivers are also useful e.g. L9110 or L298N)

13. Diode: Prevent current spikes from going to transistor (inductive kickback)
Capacitor: Reduce fast voltage transitions (100pF to 1nF), works without it

14. File->Examples->Fading

15. Servo motor

16. Example 12 – Servo Sweep
Using 5 V servo motor

17. Example 12 – Servo Sweep #include <Servo.h>
Servo myservo; // create servo object to control a servo
int pos = 0; // variable to store the servo position
void setup() {
myservo.attach(10); // attaches the servo on pin 10 to the servo object }
void loop()
for(pos = 0; pos <= 120; pos += 1) // goes from 0 degrees to 120 degrees
{ // in steps of 1 degree
myservo.write(pos); // tell servo to go to position in variable 'pos'
delay(15); // waits 15ms for the servo to reach the position
for(pos = 120; pos>=0; pos-=1) // goes from 120 degrees to 0 degrees

18. Example 13 - Turn the Servo
Use a potentiometer to determine the postion of the servo
Servo still has the same wiring just add the potentiometer as learned before

19. Example 13 - Turn the Servo
#include <Servo.h>
Servo myservo; // create servo object to control a servo
int potpin = A0; // analog pin used to connect the potentiometer (F0/A0)
int val; // variable to read the value from the analog pin
void setup() {
myservo.attach(9); // attaches the servo on pin 9 to the servo object }
void loop()
val = analogRead(potpin); // reads the value of the potentiometer (value between 0 and 1023)
val = map(val, 0, 1023, 0, 120); // scale it to use it with the servo (value between 0 and 120)
myservo.write(val); // sets the servo position according to the scaled value
delay(15); // waits for the servo to get there

20. Stepper motor

21. Stepper motor Our motor is a 12 Volt 200 step motor
With a stepper you can control speed,
direction and step amount
200 steps / 360 deg = 1 step is 1.8 deg
Bipolar motor: two windings
Red/Yellow
Green/Grey
No polarity! (no ”+” or ”-”)

22. Example 15: Stepper Motor

23. Exmaple 15 - Stepper motor 1/2
//Controlling a Stepper mtor
#define DIR_PIN 2 //Dir pin to 2
#define STEP_PIN 3 //Step pin to 3
void setup() {
pinMode(DIR_PIN, OUTPUT);
pinMode(STEP_PIN, OUTPUT); }
void loop(){
//rotate a specific number of degrees
rotateDeg(360, 1);
delay(1000);
rotateDeg(-360, .1); //reverse

24. Exmaple 15 - Stepper motor 2/2
void rotateDeg(float deg, float speed){
//speed is any number from .01 -> 1 with 1 being fastest - Slower is stronger
if (deg > 0){ // define direction according to deg (negative for reverse)
digitalWrite(DIR_PIN, HIGH); }
else{
digitalWrite(DIR_PIN, LOW);
int steps = abs(deg)*(1/0.225); //How many steps we want to take? e.g.
// 360*(1/0.225) = 1600 microsteps
float usDelay = (1/speed) * 80; //Speed defines the delay between pulses
for(int i=0; i < steps; i++){ //Toggle the step pin ON and OFF with the desired
// delay = speed
digitalWrite(STEP_PIN, HIGH); //Step pin ON
delayMicroseconds(usDelay);
digitalWrite(STEP_PIN, LOW); //Step pin OFF

25. Accelstepper http://www.airspayce.com/mikem/arduino/AccelStepper/
Install library, try example Bounce

26. Comparison of motors (Hobby) Servo
Angle is adjustable, speed is constant
Active feedback
No need for a driver DC
Speed is adjustable
No feedback
Needs a driver (or an H-bridge / transistor)
Stepper
Speed and steps (=length of the move) are adjustable
Needs a driver
Closed loop DC-motors (=servos)
Active feedback (e.g. encoder)
Drivers are recommandable
Pricy but precise

27.  The bigger the motor,  The more it costs,  The more power
Caution: Know what type of motor you need and do not pay more for attributes or power that you don’t need!