How to get started with microcontrollers - Part 2

Interfacing with a computer, controlling motors, servos etc.
Author: Aki Korhonen
Published: 06.05.2009
In English In English
Suomeksi Suomeksi

Example 2.1 - Motors

Thing to learn: switching devices on and off that need more voltage and/or current than you can supply with a microcontroller pin.

The code part is basically the same as the led on/off example in part 1. Just a few names are changed and the button works now as a toggle switch so the motor stays on with one press and turns off after the second press etc. Nothing very fancy here, just a normal transistor switch circuit to control bigger loads.

  • ATiny45
  • 100 nF capacitor
  • Push button
  • 10k ohm resistor
  • BD675 NPN-transistor (or similar with enough power handling for the motor)
  • 1N4007 diode (or similar)
  • Motor or a fan, we're going to run it on 12 volts

How to get started with microcontrollers - Part 2
Example 2.1


How to get started with microcontrollers - Part 2
Example 2.1

* MetkuMods -
* How to get started with AVR microcontrollers, part 2
* Example 2.1 - Motors
* Author: Aki Korhonen
* Date: 2009-04-29

// If clock speed isn't set in the project settings then it is set here
#ifndef F_CPU
	#define F_CPU 1000000UL // 1 MHz

#include <avr/io.h>
#include <util/delay.h>

// Motor is connected to PB4 (pin 3 on the chip)
#define MOTORPIN 4

// Button is connected to PB3 (pin 2 on the chip)
#define BTNPIN 3

int main(void)
	DDRB = 0x17; // PB3 input, others output (0x1F-0x08=0x17 or 31-8=23)
	PORTB = 0x08; // Enable internal pull-up resistor on PB3 and set others low

	uint8_t buttonPressed = 0;
		// Check if PB3 is low (button connects it to ground)
		// PB3 is normally high as it has been pulled up by the internal resistor
		if(bit_is_clear(PINB, BTNPIN) && buttonPressed == 0)
			buttonPressed = 1;

			if(bit_is_clear(PINB, MOTORPIN))
				PORTB |= _BV(MOTORPIN); // Turn motor on
				PORTB &= ~(_BV(MOTORPIN)); // Turn motor off
		else if(!bit_is_clear(PINB, BTNPIN) && buttonPressed == 1)
			buttonPressed = 0;
	return 0;

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