Tag: ISP

After making several projects with various Arduino boards, I started to use smaller and smaller boards and I ended up with a standalone processor chip. And for some applications, the standard 28-pin chip is still a bit too large. My eye had already fallen on the ATTiny85, but the 8 connection pins scared me off. But after I give the chip a good look and when I had a closer look at it, I noticed its strength. The small chip contains a full Atmega processor with flash programming memory and RAM on board with also a built-in crystal oscillator. So it is a real single chip computer
with 6 (5 effective when you want to keep the reset pin for reprogramming) in or outputs that also have additional functions such as Interrupts, PWM and analog. Each pin is freely programmable for a function and whether you want one input and five outputs or vice versa, it’s all possible with this little chip. But the chip can also communicate using I2Ch, for example to connect a screen or multiple sensors or control lights or motors with the designated PWM output pins. When I started thinking about this, I suddenly saw a lot of possibilities, the chip costs between 1 and 3 euros and can replace a complex electrical circuit. There are also a number of links on this page to sites that have done impressive things with this tiny ATTiny chip. Small boards are available with a USB port with an ATTiny85 on it, but the chip can of course also be used as a standalone chip. To program the ATTiny you will need an ISP programming board, but this is a task that our older trusted Arduno Uno can do for us. On this page there is also a small set-up board for the Arduino Uno with which the ATTiny chips can be programmed from the standard Arduino development environment.

Atmel also markets several models with the ATTiny in different housings. I’m only going to cover the the 8 pins versions here. With larger versions I quickly tend to take the 28 pins Atmega328 again because this chips is almost the same price or sometimes even cheaper. As we are used to from Atmel, there are several versions with different amounts of Flash rom and sram memory with different prices as well. By default they have a built-in RC oscillator that is not super accurate but keeps two pins free, an external crystal can also be used by sacrificing two pins oscillator to be attached. The ATtiny85 works by default on a 1 Mhz built-in RC oscillator but this can be increased by loading of the software.

Device	Flash (Mb)	RAM byte	EEPROM byte
ATtiny13	1	64	64
ATtiny25	2	128	128
ATtiny45	4	256	256
ATtiny85	8	512	512

Download the ATTiny13 datasheet.

Download the ATTiny25 /45 / 85 datasheet.

Arduino ATTiny programming

To program an Arduino you need software, the Arduino programming environment. This free development environment can be found at: download Arduino IDE here . This environment is suitable for Windows, Linux and Mac OS X. When you have connected the computer to the Arduino board wtth a USB cable, you can transfer the program code directly to the Arduino board. You can write the program on your own computer and “upload” the code to the Arduino board. All you need to do is select the board type in the menu and the port you are using on which the board is connected (when there are multiple ports). There is really only one programming language popular for the Arduino and that is the programming language C and C++. The programming environment includes a large amount of standard libraries for LCD, Servo, motors, wifi, etc. and all of these are free to download. The Arduino C version deviates from the C standard on a few points and unfortunately not all functions are present in the supplied libraries. Of course it is still an 8 bit processor and for example the support of double variables is a bit flawed. Where a standard C program starts with a main() routine, an arduino program (often called a sketch) consists of two program blocks, the setup() and the loop(). At the beginning of the program is the “void setup()” and in this function allows initialization of the program such as initialization of I/O pins, initialization of software libraries, and global variables. The setup() function is executed once by the arduino at program startup. Then it is the turn of the loop() function, it will be called endlessly until the power is turned off. From this loop() function you can call other functions and so you can build a structured program.

Arduino ATTiny default pin modes

A common source of confusion appears to be the function and numbering of the in/out pins of the aTtiny processor. I searched myself on the Internet and read the datasheets and came to the following simple overview that makes everything clear. Each pin has a different internal number and function depending on how it is configured with pinMode() and whether one uses analogRead, analogWrite, digitalRead or using digitalWrite. To make it clear I have put this in an excel sheet of which a printout is here. You don’t have to go through the internet registers to program the function of the pins, unless you want to use the alternative functions of the pins. The standard IDE and the chip definition herein will do most of the work for you when you specify the pins in the standard way.

To be able to program the ATTiny, you need an ISP programming board and these are also available in various versions. These programmers are not cheap and if we already have an Arduino Uno, we can easily use it as an ISP programmer as an extra task. You can build a small circuit on a breadboard every time you want to program an ATTiny, but when you you want to program more often, a small shield for the Arduino Uno is more convenient. We build this on a small piece of experiment print and you will need a pair of header pins, an 8 pin IC socket, a LED, one 220 ohm resistor and a 10 uF capacitor. And of course a soldering iron, solder and mounting wire, preferably in different colours.
I chose to put the solder side up, this makes soldering the headers much easier and the rest of the components can just as well be soldered on the top side. The connection wires are then hidden at the bottom.

I sawed off a piece of experimental PCB of 10 holes wide and 20 holes long. On one side is the (8) row of pins are on the far left and the other side all the way to the right. I plugged the pin rows into the Arduino first. On the power supply side and the reset pin I use the entire set of last pins, the unused pins serve as reinforcement. To polarize the board to prevent it from putting it in the wrong way I added two femnale header pins next to the male ones. On the other side the row of pins ends at the middle separation, leaving two pins free at the usb connector. Then I push the PCB over the pins and I carefully solder the pins. Don’t use too much solder, we don’t want pins to connect. Then we also bend the pins of the IC socket to the side and solder it somewhere in the middle of the PCB. I put the 1 pin on the side of the USB and power plug myself and marked it extra with a thick tip of a black marker. Then the PCB can be removed from the
Arduino Uno. At the top of the PCB (the solder side) we now put the LED and the resistor between the negative supply voltage pin and pin 5 of the ATTiny socket. Please pay attention to the polarity of the LED, you can test whether it is seated correctly by putting the plus on the pin of the foot and the minus on the header pin. Now we can do it turn the PCB over for the rest of the wiring.

We now connect pins of the power supply to the IC socket, the plus 5 volts goes to pin 8 and the Gnd to pin 4 of the socket. Now we can solder the small capacitor of 10 uF between the Gnd and the Reset pin of the Arduino Uno pay attention to the plus and the minus of the capacitor (minus to Gnd) and place the capacitor a little parallel to the header pins so that it will be sits neatly next to the Arduino chip. Now we solder the remaining wires between the Arduino Uno pins and the IC socket. Which Arduino pin to which pin of the foot is shown in the diagram below. Pay particular attention to using little solder so that there is no short circuit and if necessary, use the tip of a small screwdriver between the solder spots to remove small tin residues. Then we are going to test whether everything works by inserting an ATTiny into the socket and plugging the shield onto the Arduino Uno. Now connect Uno to the
computer with a USB cable, the Arduino Uno should work normally and the shield will do nothing. To switch the Arduino Uno to ISP programmer, let’s take the shield off again.

Adjust the Arduino IDE

To be able to program the ATtiny85 we first have to upload the ISP sketch in the Arduino Uno. You can find this sketch in example files included with the Arduino IDE which can be found in file -> Examples and the sketch is called ArduinoISP. Connect the Arduino Uno without shield to the computer and upload this sketch to the Arduino Uno in the usual way. Now let’s get the Arduino the IDE to support the Attiny. In the screen that you can find under File -> Preferences, search for the input field “Additional Board Management URL” and enter the following URL:

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

Then press the OK button to save the setting and close the screen. Then go to Tools -> Board -> Board Manager and search all the way down to the block that says “attiny by Davis A. Mellis” and click install. After installing, you should see a new board in the selection screen for the boards. Here you select the board, the processor and the choice for Arduino as ISP and then you put the shield on the Arduino. Now you can load the Blink sketch where you have to change the LED pin to 0 because we have the LED on this pin. When you connect the Arduino with the shield to the computer you should be able to upload this sketch using the normal upload button to the ATtiny, after which it will flash happily. This didn’t work for me at all and the IDE gave an error about a device number 00000, after checking it turned out that a solder connection on the IC socket was not good. After this it works fine and I could use my ATtiny85
with the blink sketch.

ATtiny with external crystal

I made a small extension to my programmer board. In one of my first experiments I made a mistake and I accidentally installed a bootloader with an external crystal after which the attiny85 chip stopped responding. So I couldn’t use the bootloader to make the ATtiny85 work on the internal oscillator again. The bootloader sets the “fuses” that determine whether the chip uses an internal or external clock. If the chip is set to external and there is no crystal, the chip will not boot. The only way to reprogram the chip is to connect an external crystal. So I decided to install an external crystal of 8 Mhz on the PCB in a small socket so that I could remove it again for checking. The crystal has a a 22 pF capacitor to ground on both legs. The capacitors can remain in place when the crystal has been removed. After placing the ATtiny85 on the board with the crystal, I selected the 1 Mh internal boatloader that I could then upload successfully after which the Attiny also worked without the crystal. By means of this extension I can now also load code that will use eventualy use an external crystal in the final circuit of the Attiny processor.

Nice ATtiny applications

Link: Tiny robot family Gallery

Link: Terminator 2 – Micro robot

Link: ATTiny Line Follower

Link: ATtiny-Powered Arduino Projects

Link: attiny – The Garage Lab

Link: ATiny mini spelcomputers

Link: ATiny automatisch fietslicht