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                                                                                        Wels, am 2016-06-12

This board is an evolution of the Arduino Uno R3 board. Identical form factor as the Uno but based on the ATmega328PB-AU, this board has much more features than the Uno. Because it is backwards compatible you can think of it as revision 4 of the Uno, which is why we called it the R4.

The circuit of the R4 is pretty close to the Uno. One of the main differences is the USB-to-serial converter for which I used an FTDI chip instead of another AVR. This saves on firmware/driver maintenance & device programming. The power supply is a bit stronger than on the Uno and of course we provided four extra connector pins to accomodate Port E of the ATmega328PB.

Here is a table that shows the main differences between the R3 and the R4.  

There are some more differences, like the touch controller. Check the datasheet for details.

Drawing up the schematic was easy enough, the hard work is in the software. Because the Arduino IDE does not know about the ATmega328PB I had to build a Boards Package that provides the toolchain. How to do this properly is unfortunately not very well documented, making this a complicated task. Also the SPI and Wire libraries had to be modified to support multiple peripherals. More details about the IDE integration can be found in the Elektor Magazine article published in June 2016.

Note that this Boards Package is intended for Windows only, Linux and Mac users can use it in a virtual machine. To port the package to Linux and Mac, the toolchain avr-gcc v4.9.2 must be replaced by a version compiled for Linux/Mac. The Boards Package can be downloaded from the Elektor.Labs space at GitHub.

Installation

Use the Arduino IDE (v1.6.6 or higher, do not use an IDE from arduino.org) Boards Manager to install this package, as follows:

1. Open the Arduino IDE's Preferences dialog: File -> Preferences
2. Add the URL https://raw.githubusercontent.com/ElektorLabs/arduino/master/package_elektor_boards_index.json to the edit box "Additional Boards Manager URLs". (It is possible to have multiple URLs as long as you separate them with commas.) This URL is long and finishes with "json", make sure you copy all of it. You can also copy it from here.
3. Open the IDE's Boards Manager: Tools -> Board -> Boards Manager
4. As Type (upper left corner) select Contributed. You should now see at least one entry for Elektor boards.
5. Click on the entry that you want to install to make the install button appear.
6. Click the Install button to install the boards.
7. Close the dialog when done.
8. Now when you open the available boards list (Tools -> Board) there will be a header "Elektor Labs" followed by the Elektor boards. Choose the one you need.

Note that I use the IDE 1.6.7 for Windows, Arduino IDE 1.6.8 should be avoided because it has a serial port issue.

Now that I have the R4 properly integrated in the Arduino IDE, I find that I use it all the time while my "old-skool" R3s are gathering dust. Especially the R4's second serial port is really handy and makes debugging sketches much easier. Also, using it in 3V3 mode saves a lot of hassle with level shifters. Officially the MCU is not specified for 3V3 @ 16 MHz, but for me it works fine. If it doesn't it is easy enough to replace the crystal by an 8 MHz one (and replace the bootloader!).

New peripherals in sketches

The Elektor Uno R4 has more hardware peripherals than the R3 and so the Arduino libraries have been upgraded to support them. In your sketches you can now use:

• Serial and Serial1 
• I2C0 and I2C1 (include the Wire library), I2C defaults to I2C0
• SPI0 and SPI1 (include the SPI library), SPI defaults to SPI0
• digitalRead/Write now also work on pins 20 to 23 (port E)
• analogWrite now also works on pins 0, 1 and 2
• analogRead accepts A6 and A7

Quelle:

https://www.elektormagazine.de/labs/elektorino-uno-r4-150790

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