Exercise 11

15.04.2015

Output Devices

Assignment

• add an output device to a microcontroller board you've designed and program it to do something

Servo motor

During this week I tried to make a board that will be useful for my final project.
In the final project I need a little board that control a micro servo to up and down the tool (a pen for example) and maybe do a Z position with a potentiometer
To make this board I won't to use an atmega328 because is much, so I decided to use an Attiny44. I saw the datasheet and schematic during past week and I think that is perfect for this scope.

I started planning what the board will do:

- Read a potentiometer
- move the servo in the position read from potentiometer
- listen a signal in a digital pin
- if digital pin is High put servo in 0 position
- if digital pin is low put the servo in the position mapped from potentiometer

I designed the board in Eagle starting from an Hello Board
  

As described above I connected
PIN 4 -- LED
PIN3 -- INPUT
PIN2 -- POTENTIOMETER
PIN 7 -- SERVO

I also wired some power aux to power eventually some tools

Here you can download the EAGLE FILES

The sketch is simple and I started using the Servo library example.
But I discovered that the standard servo library doesn't work with Attiny and I have to use another library called SoftwareServo
this is the code to control my board

	/* Sketch to control the pen position in OPENstage */

#include 

SoftwareServo myservo;  // create servo object to control a servo

int pos = 0;
int potpin = 2;  // analog pin used to connect the potentiometer
int val;    // variable to read the value from the analog pin
int Zup;
bool Zadj; // if true I can adjust servo position by potentiometer
int prevVal;
int zeta;


void setup()
{
  Zup=10;   //servo at 10 degree for pen in high position
  

  myservo.attach(7);  // attaches the servo on pin 9 to the servo object
  myservo.write(Zup);  //Put servo at 10 angle
  SoftwareServo::refresh();
  Zadj=true;  //adjust servo position with potentiometer
  goDown = true;
}

void loop() {
  
 prevVal = val;

  val = analogRead(potpin);            // reads the value of the potentiometer (value between 0 and 1023) 
  val = map(val, 0, 1023, 0, 180);     // scale it to use it with the servo (value between 0 and 180)
 
  if ( digitalRead(3)==LOW){  //pen in high position (maybe M09 from gcode)
  

  
  myservo.write(Zup);  //Put servo at 10 angle
  SoftwareServo::refresh();

    

  }else
   if ( digitalRead(3)==HIGH){  //pen in low position (maybe M08 from gcode)

    
      myservo.write(val);   //if Pin IN is HIGH servo UP
      SoftwareServo::refresh(); 
      
  }
               
  delay(15);                           // waits for the servo to get there 
} 

To program the board I used Arduino IDE as described in THIS LINK

this is the board that I have soldered

The board have a little noise that I try to cancel with a capacitor, below there is a little video that show how it works