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  • Author Author: shabaz
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Arduino Uno Rev4 Minima and WiFi – any good?

shabaz


I just saw the schematics of the new Arduino Uno R4 have been released. There are two versions, a R4 Minima , and a R4 WiFi .

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(Image source: https://www.arduino.cc/ )

The Uno R4 boards use a Renesas RA4M1 series chip, specifically R7FA4M1AB3CFM#AA0 :

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(Table source: Renesas website)

Some info on the chip functionality is here: Working with the Renesas RA4M1 Microcontroller  

There are a series of blog posts on the RA4M1 chip here: /tags/RA4M1 (currently the blog posts are about the 100-pin chip version instead of the 64-pin version, but the information is still relevant, it’s the same part with less connections brought out).


Compared to the Uno R3, the Uno R4 Minima schematic (PDF) is cleaner, since the board is simplified through the use of the RA4M1 microcontroller:

image (Schematic source: https://www.arduino.cc/ )

Most obviously, now there’s no need for the separate Atmel chip that was on the older R3 board, which acted as the interface between USB and the serial port on the ATmega328 microcontroller. Instead, the R4’s newer RA4M1 chip has the USB-C connection directly connected to it.

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If the default firmware ever goes wrong on the Uno R4 board, or if the Arduino environment is not needed for a project, then there is a mode pin, labelled MD on the RA4M1 chip, which can be seen in the circuit above, it is connected to a test pad. It can in theory be connected to 0V to force the RA4M1 to run its built-in bootloader! There is also an SWD connector, so a decent debug tool could be used.

A good touch is the decent DC-DC converter, so that the board can be powered from 6-24V input, and it can power a fair bit of external hardware with its 5V output. The ISL854102 chip supports designs for up to 1.2A and 40V inputs. This is a massive benefit compared to the older Uno R3 which couldn’t supply a lot of current when powered from the barrel connector, and often needed a lower voltage supply, for instance, 7V or 9V, to prevent overheating. With the R4 boards, this problem is gone.

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I hope the resistors on the FB pin are large (for instance, 0603 sized), so that users can hack the board for 3.3V operation instead of 5V. I think this is the biggest annoyance with the Uno R4; it is a 5V board like the R3. I can imagine level converter shields becoming useful to work around that (see the following blog for another solution!  Modifying the Arduino Uno R4: Making it 3.3V-Friendly ) 

The Uno R4 WiFi has a lot more circuitry but the same core circuit as the Minima. According to the Uno R4 WiFi circuit (PDF) It has two additions; wireless, and LEDs! (However, it has a subtraction; no SWD connector for an external debugger tool).

  has noticed that the Uno R4 WiFi also has a Qwiic connector on-board too, which is used for connecting up I2C devices).

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The Uno R4 WiFi uses the same DC-DC converter as the Uno R4 Minima but also has a 3.3V linear regulator feeding off that, and it is used to power up an ESP32-S3-MINI-1 module. The module only seems to be wired for WiFi/Bluetooth, interfaced through level translators, and the ESP32 3.3V GPIO is not accessible otherwise, as far as I can tell, so if you need 3.3V interfacing for external hardware, then you’ll still need your own level translator.

The LEDs are in a matrix, directly driven from the RA4M1 chip. Maybe they ought to have been on the underside of the board, I don't know.

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Is anyone thinking of getting a Uno R4 board (or two!) to experiment with it? For me, I think it’s the first time in ages that I wish to use an Uno board (although I’m working on my own RA4M1 dev-board for different purposes), because the chip is powerful, and one can do a lot with it. The DC-DC converter is a nice touch, simplifying Uno usage in projects.

One other thing is that the pricing looks affordable, compared to how overpriced the older Uno R3 is. The RA4M1 chip has very nice features built-in, for instance, analog interfacing peripherals (specifically a 14-bit ADC, 12-bit DAC, and even built-in op-amps). As mentioned, the decent DC-DC converter too is a very worthwhile enhancement over the older board too.

Interested to hear opinions, and upsides/downsides to these new boards...

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