Arduino Uno R4 review

By Ben Everard. Posted 12 months ago.

Thirteen years ago, Arduino released its ninth board, and for reasons only it knows, it decided to call the board Uno. It quickly became synonymous with maker electronics projects.

This fourth iteration (Arduino Uno R4, from €18) includes by far the biggest changes to date, not least because, for the first time, there are two options: the Minima, which is a fairly bare microcontroller board (in the same style as earlier Unos), and the Wi-Fi version that includes both a wireless networking controller and a grid of 96 LEDs.

The other big change is that the microcontroller has been swapped. The AVR-based ATMega controller is replaced by an Arm-based Renesas chip. This is a major upgrade in almost every way. It’s faster, has more RAM, more storage, more peripherals (including a digital-to-analogue converter). We don’t have space to list every feature here, but it’s generally more capable. However, when shifting not just the microcontroller family, but the architecture of the core, it’s going to end up working a bit differently.

The Arduino libraries do quite a good job of abstracting away the hardware, and code can often run on different hardware without modification. However, some programmers seeking to squeeze every drop of performance out of the AVR boards use code that is platform-specific. As a result, not all code written for the Arduino Uno R3 will work on the R4.

This aside, though, Arduino has done a good job of ensuring compatibility with the R3. The pinout is the same (with some added peripherals), and the microcontroller operates at 5 V (the vast majority of Arm microcontrollers operate at 3.3 V). This means that, as long as the software works, the hardware should too.

While the 5 V GPIOs are great for compatibility with existing Uno hardware, the world has moved on in the past 13 years, and most electronics now expect 3.3 V. The R4 Wi-Fi does have a pair of 3.3 V GPIOs in the Qwiic connector which should make it easy to connect to I2C hardware, especially those with a Qwiic or STEMMA QT connector. However, this isn’t on the Minima. Otherwise, you need to ensure that any hardware you want to use is compatible with 5 V.

One slightly unusual feature of this, and some other official Arduino boards, is that it comes with a transparent plastic mounting plate. While this might seem like a trivial thing, it does have some useful features. At the very least, it stops the contacts on the bottom from shorting out if you place the board on something conductive (such as the leg you trimmed off a soldered LED and missed when you tidied your desk).

Both the Minima and Wi-Fi version of the R4 have the same footprint

The mounting plate has a few more tricks up its sleeve too. It mounts your Uno on your project quite securely, yet still lets you unclip it without screws. The screw holes on the clip match the mounting points on the Uno, so you can screw through and it acts as a standoff. It also has another set of sunk screw holes so that you can screw in the clip without interfering with the Uno. Additionally, it has clips to attach it to a breadboard (on either side) so that jumpers don’t pull out when you accidentally knock the board.

While Arduino software support is generally excellent, it feels like, in recent years, boards have come with features with little to no documentation. In the case of the R4, that’s the on-board OpAmp. It apparently exists but, at the moment, there’s no information on how to use it. This isn’t necessarily a big deal because OpAmps are hardly essential features of microcontrollers. However, given that it’s an advertised feature (and one we’d be really interested in trying), it’s a bit disappointing that there’s no information on how to actually use it.

The R4 is a natural successor to the R3. Some people will complain that it should have stayed on an AVR microcontroller, but the gulf in performance between AVR and Arm chips means that this is increasingly not viable.

It’s a reminder that smallness isn’t always a feature – it’s a design choice that comes with positives and negatives, and the trade-off isn’t always worthwhile. In a world where many dev boards are compressed so much, pins are labelled in minute fonts. On the Uno, each pin is labelled three times to make sure you know exactly where you’re poking the wires. It comes with a mounting plate that’s actually useful.

When the original Uno was released, it quickly became the standard microcontroller because, frankly, the other options weren’t great. We’re now living in a golden age of microcontroller dev boards, where there’s a myriad of choices. Many of them are really well-thought-out and have great software support. For the Uno to continue to stay relevant, it needs to stand out. If you’re looking for a 5 V microcontroller, a classroom microcontroller, or an Uno form-factor microcontroller, then the R4 is still a great choice.