An Arduino UNO shield for Attiny85 Programming.

Programming ATtiny boards can be a tiring labor, so make it faster and easier with this shield!

Step 1: Add Support for the ATtiny85 to the Arduino URL Board Manager

By default the Arduino IDE does not support the ATtiny85 so it's required to add support for the Attiny85 to the Arduino Board Manager:

From the Arduino IDE Go to Arduino->Preferences then scroll down to Additional Board Managers URLs

Copy & paste the following (if you already have a board manager URL just add a comma before pasting)

https://raw.githubusercontent.com/damellis/attiny/ide-1.6.x-boards-manager/package_damellis_attiny_index.json

Press "OK" at the bottom then restart the Arduino IDE

Step 2: Install the ATtiny Board Package From the Arduino IDE go to Tools--> Board-->Boards Manager 

A new tab will open and at the top of the tab type: attiny 

Select Install on the Attiny by David. A Mellis 

Restart the Arduino IDE 

The ATtiny85 board should now be added ! Go to Tools--> Board-->Attiny85

Step 3: Set the Arduino Uno Into ISP Mode

Since what we want is to be able to program the ATtiny85 from the Arduino IDE which requires to burn the bootloader to the ATtiny85 we will need to "prep" the Arduino fist by uploading the ISP sketch to it.

In the Arduino IDE select File-->Examples--> 11. Arduino ISP-->ArduinoISP 

the ISP sketch should open and upload it to your Arduino Uno

Step 4: How a Microcontrollers Pins Are Labeled

Before the connections are made there is a very important fact to know how pins on microcrontrollers/ICs are labeled. 

Pin numbers used to program a chip on the Arduino IDE are based on how the chip manufacturer has internally named/aranged the pins . The manufacturer of the ATtiny85 is ATMEL (the AT in ATtiny85-actually stands for ATMEL);It's common for chips to have the first two initials of the company who makes them.

Pins are gathered into groups called "ports" these ports are labeled A,B,C etc. Each port has a number of pins which are labeled 0,1,2,3 etc and stick out on different parts of the chip which is why a microcontroller's physical pin often time will be different than the pin number used when programming the chip.

An example:

PB0 (in the above datasheet) just means pin 0 is located on Port B of the Chip.

If pin 0 was located on Port A the name would look something like PA0 (Port A pin 0)

To add to the complexity pins can have more than one fuction and be labeled multiple names. 

Wrapping it all together! :

Writing a program to light an LED on pin 0 on the ATtiny85 might be confusing at first because just by looking at the chip , there is no pin 0! However, by checking the datasheet of the ATtiny85 from ATMEL-snippet shown above-pin 0 is internally located on the chip's port B (and is actually the chip's physical pin 5 )!

Step 6: Making the ATtiny85 Arduino Compatible

By default any fresh microcontroller chip bought will not be able to be programmed with the Arduino IDE out of the box. This is why it's required to burn the Arduino bootloader onto the chip to make sure the chip will accept any programs uploaded via the Arduino IDE. 

Quick checklist before pressing "burn bootloader"

 Go to Tools -> Board scroll to the bottom select ATtiny25/45/85 

 Under Tools -> Processor--> 8 MHz (internal) 

Under Tools-->Programmer-->Arduino as ISP 

Check that all wiring, capacitor, and board selections are correct 

Finally select  Burn Bootloader

leave the wires connected they will be used in the next step

A message will appear saying "Done Burning Bootloader"

Step 7: Uploading the Blink Sketch

Test that the ATtiny85 can now receive sketches from the Arduino IDE by uploading the blink example

Go to File-->Example-->01.Basics-->blink 

Edit the sketch by replacing pin 13 with 0 

Make sure to still have the ATtiny85 board settings from the previous step selected 

Make sure all wiring is the same as the previous step 

Upload the sketch 

Wire an LED by connecting the anode to pin 0 (physical pin 5 ) and the cathode to a 1K resistor connected to ground (physical pin 4) 

While a resistor is not needed since the battery provides 3v (not enough to blow up an LED) it is recommended to lower the brightness of the LED.

Hope it helps on future projects!