How to: program ATtiny85 via Arduino

Configure Arduino as ISP

• connect Arduino to the PC.
• open Arduino IDE.
• open the ArduinoISP example file (File > Examples > ArduinoISP).
• note: if using Arduino Mega, modify the following lines from:

#define RESET       10
#define PIN_MOSI    11
#define PIN_MISO    12
#define PIN_SCK     13

to:

#define RESET       53
#define PIN_MOSI    51
#define PIN_MISO    50
#define PIN_SCK     52

• upload sketch.

Add ATtiny board to Arduino IDE

• go to File > Preferences.
• in the Additional Boards Manager URLs, add:

http://drazzy.com/package_drazzy.com_index.json

• go to Tools > Board > Boards Manager.
• search and install ATTinyCore.

Connect ATtiny to Arduino

• connect according to the table below:

ATtiny85 pin	Arduino Uno pin	Arduino Mega pin
VCC	5V	5V
GND	GND	GND
RESET	10 (SS)	53 (SS)
PIN 0 / MOSI	11 (MOSI)	51 (MOSI)
PIN 1 / MISO	12 (MISO)	50 (MISO)
PIN 2 / SCK	13 (SCK)	52 (SCK)

• add a 10uF capacitor between RESET and GND on Arduino, to avoid auto-reset while uploading program to ATtiny85.

Upload program to ATtiny85

• go to Tools > Board.
• configure as follows:

Board: "AtTiny25/45/85"
Processor: "AtTiny85"
Clock: "Internal 1 MHz"
Programmer: "Arduino as ISP"

• burn bootloader (Tools > Burn bootloader)
• upload the following program:

int led = 0;
void setup() {
  pinMode(led, OUTPUT);
}
void loop() {
  digitalWrite(led, HIGH);
  delay(1000);
  digitalWrite(led, LOW);
  delay(1000);
}

Test Blink program

• remove all connections except for VCC and GND.
• add a LED between ATtiny pin 0 and GND.