11. Output devices

Assignment

group assignment : measure the power consumption of an output device

individual assignment : add an output device to a microcontroller board you’ve designed, and program it to do something

Board design

About MOSFET

MOSFET means Metal Oxide Semiconductor Field Effect Transistor. There is two types of MOSFET : N or P-channel. There both have three pins : Drain, Gate, Source.

N-Channel MOSFET	P-Channel MOSFET

Warning

Small arrow indicate direction of electron flow

Specifications :

Vgs : voltage between Gate and Source. Vgsth is Vgs min to unlock MOSFET (it’s a range) and Vgs should not exceed Vgsmax given by the datasheet.

if Vgs < Vgsthmin : MOSFET is blocked.

if Vgsmax > Vgs > Vgsth(max) : MOSFET is passing.

Id : drain current. Depend on temperature. Id should be lower than Idmax given by the datasheet.

Rdson : electrical resistance between Drain and Source when MOSFET is passing.

Vds = Rdson x Id : voltage between Drain and Source

To use MOSFET as a switch we should have the smallest Vds and that for, the smallest Id and the biggest Vgs.

Here I use first MOSFET IRF740 and find some informations in the datasheet here.

Channel type	Vgsthmin	Vgsthmax	Vgsmaw	Id	Rdqon
N	2V	4V	+-20V	10A at 25°C

So with this MOSFET I use 0 volt to block MOSFET and 5V to unblock it.

You can find more about MOSFET here.

TinkerCad simulation

You can find the TinkerCad file here.

// C++ code
//
int counter;

void setup()
{
  pinMode(2, OUTPUT);
}

void loop()
{
  for (counter = 0; counter < 10; ++counter) {
    digitalWrite(2, HIGH);
    delay(4000); // Wait for 4000 millisecond(s)
    digitalWrite(2, LOW);
    delay(6000); // Wait for 6000 millisecond(s)
  }
}

Test with Arduino UNO

Here motor is replaced by an air pump.
Diode added as described on schema before. Used to avoid disturbance using air pump.

Board design

Board production

Output devices

Air pump

I use a AIRPO D2028B pump described here.

Speaker

I use a PWM output to modulate output signal which can’t be analogic with our micro. PWM means : Pulse Width Modulation.

So I use a digital output which has only two values (HIGH 5V and LOW 0V).

With PWM output you can have modulation by changing HIGH and LOW values very quickly : you can have 256 different values generated by average from HIGH and LOW periods (from 0 to 255).

PWM = 0 > 0V	PWM = 25 > 0.5V	PWM = 75 > 1.5V	PWM = 255 > 5V

To calculate Voltage you make a cross product.

For example PWM = 75

75 / 255 x 100 = 30%

30 / 100 x 5V = 1.5V

PWM	%	V
PWM = 0	0%	0 V
PWM = 25	10%	0.5 V
PWM = 75	30%	1.5 V
PWM = 100	40%	2 V
PWM = 255	100%	5 V

More informations about PWM here.

How to program PWM output :

int broche_PWM = 3;
int Valeur_PWM = 0;

void setup()
{
  pinMode(broche_PWM, OUTPUT); // Pin 3 (named broche_PWM) as PWM output
}

void loop()
{
    analogWrite(broche_PWM, 0); // 0% sent on broche_PWM > 0V
    delay(4000); // Wait for 4000 millisecond(s)
    analogWrite(broche_PWM, 25); // 25% sent on broche_PWM > 0.5V
    delay(4000);
    analogWrite(broche_PWM, 50);
    delay(4000);
    analogWrite(broche_PWM, 75);
    delay(4000);
    analogWrite(broche_PWM, 100);
    delay(4000);
    analogWrite(broche_PWM, 125);
    delay(4000);
    analogWrite(broche_PWM, 150);
    delay(4000);
    analogWrite(broche_PWM, 175);
    delay(4000);
    analogWrite(broche_PWM, 200);
    delay(4000);
    analogWrite(broche_PWM, 225);
    delay(4000);
    analogWrite(broche_PWM, 255); // 100% sent on broche_PWM > 5V
    delay(4000);
}

I test an other function to generate modulate output :

tone(pin, frequency, duration).

I use frequencies of a pentatonic scale :

note	frequency
ré#	311 Hz
fa	349 Hz
sol	392 Hz
la	440 Hz
si	494 Hz

void setup()

// ajouter l'initialisation

void loop()
{
    tone(3, 311, 500);
    tone(3, 349, 500);
    tone(3, 392, 500);
    tone(3, 440, 500); // La 440
    tone(3, 494, 500);
}

DC Motor

I change speaker by DC motorand use PWM program seen before.

int broche_PWM = 3;
int Valeur_PWM = 0;

void setup()
{
  pinMode(broche_PWM, OUTPUT);
}

void loop()
{
    analogWrite(broche_PWM, 0);
    delay(4000); // Wait for 4000 millisecond(s)
    analogWrite(broche_PWM, 25);
    delay(4000);
    analogWrite(broche_PWM, 50);
    delay(4000);
    analogWrite(broche_PWM, 75);
    delay(4000);
    analogWrite(broche_PWM, 100);
    delay(4000);
    analogWrite(broche_PWM, 125);
    delay(4000);
    analogWrite(broche_PWM, 150);
    delay(4000);
    analogWrite(broche_PWM, 175);
    delay(4000);
    analogWrite(broche_PWM, 200);
    delay(4000);
    analogWrite(broche_PWM, 225);
    delay(4000);
    analogWrite(broche_PWM, 250);
    delay(4000);
    analogWrite(broche_PWM, 500);
    delay(4000);
}

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Last update: May 13, 2022