Fullscreen HTML5Med Res (??MB)HTML4

Review by Jim Rowe Arduino UNO R4 Minima A leap forward for Arduino The R4 is the latest version of the ubiquitous Arduino Uno. It is a major upgrade as it has a 32-bit microcontroller, part of the Renesas RA4M1 series, with 256kB of flash, 32kB of SRAM and 8kB of EEPROM; significantly more than previous versions. Other features include a DAC with 12-bit precision, an ADC with 14-bit precision, a USB 2.0 full-speed module and a real-time clock. T he Arduino Uno R4 Minima resembles earlier versions, such as the Uno R3. The PCB is identical in size (68 × 53mm) and shape, and the SIL header sockets along the sides are compatible with those of the R3 and earlier versions. However, if you look a bit closer, significant differences become apparent. For a start, the USB connector at the top is now a USB-C socket rather than the Type-B socket used in earlier versions. There are also fewer components visible; for example, only two ICs instead of four, and no power transistor or large electrolytic capacitors. The Uno R4 Minima is undoubtedly a big step up from its predecessors like the Uno R3 and the Nano. The main reason for the improvements is that the R4 Minima no longer uses an Atmel ATmega328P 8-bit microcontroller, but is now based on a much faster and more powerful microcontroller: the Renesas R7FA4M1AB#CFM#AA0. This is part of Renesas’ RA4M1 series, a 32-bit micro with a 48MHz ARM Cortex core. As shown in the block diagram, Fig.1, the R7FA4M1 also has much more internal memory than the ATmega328: 256kB of flash vs 32kB, 32kB of RAM vs just 2kB, and 8kB of EEPROM for data storage compared with just 1kB. So it has eight times the flash, 16 times the RAM and eight times the EEPROM. But that’s just for starters. The R7FA4M1 also includes a floating-­point 24 Silicon Chip unit (FPU) for faster mathematical calculations, a USB 2.0 full-speed module, a 14-bit ADC (analog-to-­ digital converter) compared to 10-bit in the ATmega328 and a 12-bit DAC (digital-­ to-analog converter), which the ATmega328 lacked entirely. It also has an RTC (real-time clock) module, a CAN communications module, and the familiar UART, I2C and SPI serial interfaces. The CAN port does need an external transceiver, though. With a clock rate three times that of the older ATmega328, we expect it to be more than three times faster since its word size is four times larger (32 bits vs 8 bits). The floating point unit should make the gulf in performance even larger when working with decimal floating point numbers. There are also four on-chip op amps (another feature the ATmega328P lacked) and a temperature sensor, plus a choice of six different on-chip clock oscillators: a main clock oscillator, a sub-clock oscillator and high, middle and low-speed clock oscillators, plus a 15kHz on-chip oscillator dedicated to the independent watchdog timer (IWDT). There’s a clock trim function for the high, medium and low-speed oscillators. The R7FA4M1 has two hardware SPI (serial peripheral interface) serial units, two I2C interfaces and four SCI (serial communications) interfaces. Also, the R4 Minima can easily simulate a mouse, keyboard or other HID Australia's electronics magazine (human interface device) when connected to a computer via a USB cable. The new 12-bit DAC gives the R4 Minima the ability to produce analog signals and waveforms without using PWM (pulse-width modulation). That means that the R4 Minima can generate cleaner audio signals and waveforms. It also means that the R4’s six PWM outputs can be used for other things like driving LEDs and Mosfets. Another feature of the R7FA4M1 MCU is its serial wire debugging support. It has a very small 5×2-pin DIL header near the 3×2-pin in-circuit serial programming (ICSP) header, labelled “SWD”. Serial Wire Debug is a modified version of the JTAG protocol, designed specifically for ARM processors. It means that, with the right hardware and software, you can monitor and even pause the operation of the processor core without using or affecting any of its I/O pins. As you can see, the R7FA4M1 microcontroller is very powerful indeed. All those feature are packed inside an unassuming 64-pin LQFP package measuring only 12 × 12mm, including the leads on all four sides. For more information you can view the Uno R4 Minima data sheet at: siliconchip.au/link/abq0 Other features But wait, there’s more! (No, you don’t get a free set of steak knives…) Like the earlier versions, the R4 siliconchip.com.au Minima can be powered with 5V via the USB socket, or it can be powered via either the concentric barrel connector or the VIN pin. In the latter cases, it can handle a DC voltage between 6V and 24V. That wide range is thanks to the Renesas ISL854102FRZ-T buck converter chip (the second IC on the module PCB, up near the concentric power connector), which retains good efficiency even at higher input voltages. As a result, the R4 Minima can be powered from almost any external DC power source of no more than 24V. Schottky diodes are also provided for reverse polarity and overvoltage protection. Another nice feature of the R4 Minima is that it has a five-in-one ESD protection diode between the pins of the USB socket, to protect the micro and the rest of the module from electrostatic damage. The device used is a Nexperia PRTR5V0U2X, which includes two pairs of ultra-low-capacitance diodes between the USB D- (DM) and USB D+ (DP) signal lines and the USB+5V and ground lines. There is an additional ESD protection diode between the two power lines to ensure signal line protection, even if no supply voltage is present. So the Arduino Uno R4 Minima is a really impressive step up from the R3 and earlier Unos. It has a faster and more powerful MCU with much more memory and many additional features like an inbuilt USB 2.0 interface, a realtime clock and a 12-bit DAC capable of providing smooth audio signals, plus the ability to run from a wide range of power sources. Fig.1: the block diagram for the Renesas R7FA4M1AB#CFM#AA0 32-bit ARM Cortex microcontroller. One of the biggest improvements over the old ATmega328P is the extra storage space (256kB vs 32kB of flash etc). How about compatibility? As you can see from the pinout diagram in Fig.2, the R4 Minima is basically hardware-compatible with the earlier versions of the Arduino Uno. So, it should be capable of interacting with most shields designed to work with the earlier versions, especially if they have the same operating voltage. However, in their product reference manual, Arduino states that they cannot guarantee that all sketches and libraries intended for use with earlier versions will be fully software compatible with the R4 Minima because of the significantly different microcontroller used. They advise that all sketches developed to run on the Uno R3 siliconchip.com.au Fig.2: the pinout diagram for the Arduino Uno R4 Minima. The board layout is designed so that it is hardware-compatible with the earlier versions of the Arduino Uno and its shields. Australia's electronics magazine December 2023  25 should run on the R4 Minima, provided that they were developed using the Arduino API. Still, changes will be needed if your sketch uses instructions only suitable for the AVR architecture. Similarly, they advise that not all libraries written to suit the Uno R3 would be compatible with the R4 Minima. Apparently, some libraries have already been ‘ported over’ as part of their early adopters program. Arduino has already produced eleven tutorials demonstrating the various special features of the R4 Minima, plus a guide to popular shields and their compatibility with it. These are all available on the Arduino website, at siliconchip.au/link/abq1 The titles are: 1 2 3 4 5 6 7 8 9 10 11 Getting Started with Arduino Uno R4 Minima Arduino Uno R4 Minima Real Time Clock Arduino Uno R4 Minima ADC Resolution Arduino Uno R4 Minima Digital-toAnalog Converter (DAC) Arduino Uno R4 Minima EEPROM Arduino Uno R4 Minima USB HID Arduino Uno R4 Minima CAN Bus Arduino Uno R4 Minima Shield Compatibility Arduino Uno R4 Minima Cheat Sheet Arduino Uno R4 Shield Guide Debugging the Arduino Uno R4 Minima One was that the analog output of the DAC appears on pin A0 of the Minima; another was that in the Arduino programming language, the simplest way of programming the DAC is by using the instruction analogWrite(A0, value); where ‘value’ can be any integer value between 0 and 255. Why only values between 0 and 255? That’s because, although the DAC does have a resolution of 12 bits, the Arduino firmware gives it a default resolution of 8 bits. If you want to increase it to the full 12 bits, this can be done in the Setup() section of your sketch by using this instruction: analogWriteResolution(12); This allows you to feed the DAC with values between 0 and 4095, rather than the previous 0 to 255. Armed with this basic information, I worked through the examples in the Arduino tutorial on the Uno R4 Minima’s DAC. There were three example sketches (see github.com/ arduino/ArduinoCore-renesas/ blob/main/libraries/AnalogWave/ examples/), all using a library called analogWave. The first sketch generates a nominal sine waveform, the second plays “Frere Jacques”, while the third generates any of the 88 notes on a piano keyboard. All three allow output frequency adjustment by varying the voltage fed to the A5 analog input pin using a potentiometer connected between +5V and ground. The analog output from A0 can be either fed directly to a small piezo sounder or the input of a small amplifier driving a speaker; I used a tiny low-cost amplifier module based on an LM386. Scope 1: the output of the sketch “DACEqual­ TemperedScale” which generates a 3.788kHz sinewave. Trying it out I ordered an Arduino Uno R4 Minima from a supplier on eBay. It cost me US$20, roughly $31 at the current exchange rate. It arrived about 10 days later. First, I tested its compatibility with some sketches I had written for the Uno R3 and found that they ran just fine. The only thing I had to change was to install the latest version (2.2.1; siliconchip.au/link/abq2) of the Arduino IDE, because the version I had been using (1.8.19) had trouble uploading sketches to the Uno R4 Minima. I think that was because the USB interface of the R4 Minima is built into the R7FA4M1 MCU itself, rather than in a separate chip as in the R3 and earlier versions of the Uno. I then decided to try one of the R4 Minima’s interesting new features: the DAC. I learned a few basic facts by reading the information on this in the Renesas RA4M1 data sheet (pages 1149-1156; siliconchip.au/link/abq4) and the brief information in the Arduino ‘Cheat Sheet’ on the R4 Minima (siliconchip.au/link/abq3). 26 Silicon Chip Scope 2: the output of the sketch “Using_ the_R4_DAC_to_ gen_a_sawtooth. ino” which generates a sawtooth wave with 63 rising steps followed by a singlestep fall. Scope 3: the output of the sketch “Using_ the_R4_DAC_to_ gen_a_sinewave.ino” which generates a smoother sinewave than the one shown in Scope 1. Australia's electronics magazine siliconchip.com.au All three sketches use a previously calculated set of samples to produce a sine waveform, called wave.sine(freq). Although the sketches all worked, they did generate rather rough and noisy waveforms, with a significant amount of accompanying noise and harmonic content. Scope 1 shows the output from the first sketch generating a 3.788kHz sinewave. When I looked around on the Uno R4 Minima section of the Arduino Forum, I found others expressing reservations about the performance of sketches using the analogWave library. There were also a few suggestions on how to get the R4 DAC to produce smoother and cleaner waveforms, from contributors like “Grumpy Mike” and “susan-parker”. Ms Parker (who also calls herself ‘TriodeGirl’) seems to be a very experienced programmer who has produced her own sketch, using direct register setup and interrupts. She explained that one of the reasons why the analogWave library produces noisy or ‘hairy’ waveforms is because it performs DAC initialisation each time it is called. I also found a sketch from a contributor calling themselves “daueb” that didn’t make use of the analogWave library at all but instead used the basic instruction analogWrite(A0, value). After looking at daueb’s sketch, I decided to write a small sketch of my own to test the R4 Minima’s DAC. The sketch is called “sketch_for_ testing_the_R4_DAC.ino”, and all it does is prompt you to feed in a value between 0 and 255 via the Arduino IDE’s Serial Monitor, after which it feeds this value to the DAC so you can measure the output voltage from the A0 pin using a DMM. The sketch uses the default DAC resolution of eight bits but also has provision for changing to 12 bits if you want. Fig.3 shows what I found when I used this sketch to plot the output of the R4 Minima’s DAC over the full range of input values from 0 to 255. It is basically a straight line from 0.0034V to 4.7468V. Encouraged by this result, I wrote a small sketch to generate a linear sawtooth waveform, again using the analogWrite(A0, value) instruction suggested by daueb. It is called “Using_the_R4_DAC_to_gen_a_sawtooth.ino”, and like the first sketch, you can download it from siliconchip. com.au/Shop/6/306 siliconchip.com.au Fig.3: the output from the Arduino sketch “sketch_for_testing_the_R4_DAC.ino”, which plots the output for the R4’s DAC over an input range of 0 to 255. This sketch generates a sawtooth wave consisting of 63 rising steps followed by a single-step fall; the result is shown in Scope 2. You can vary the number of upward steps simply by changing the step size in the ‘for’ instruction inside the sketch’s loop(): for (x = 0; x < 255; x += 4) A smaller value in the place of 4 will give a smoother sawtooth (at a lower frequency), while a larger value will give a ‘staircase’ sawtooth at a higher frequency. Next, I came up with a similar small sketch to generate a sine waveform, called “Using_the_R4_DAC_to_gen_a_ sinewave.ino”. Scope 3 shows the waveform that this sketch can produce – it’s much smoother than the waveform in Scope 1, but much lower in frequency. As before, you can change the waveform’s smoothness and frequency simply by changing the step size in the ‘for’ instruction inside the sketch’s loop: for (deg = -180; deg < 180; deg += 5) If you increase the step size from 5 degrees to, say, 10 degrees, you’ll get a more stepped sinewave at a Australia's electronics magazine higher frequency. If you decrease it to, say, 1 degree, you’ll get an even smoother sinewave but much lower in frequency. So there you have a demonstration of the basic trade-off when you are trying to generate waveforms using a DAC: decreasing the step value gives greater waveform smoothness but also lowers the frequency. These simple sketches are only suitable for generating smooth waveforms at low frequencies. Unfortunately, those using the analogWave library are not much better. As far as I can see, the only way to get smoother waveforms at higher frequencies from the Arduino R4 Minima’s DAC would be to use Ms Parker’s approach, using direct register setup and interrupts. You can find her sketch on GitHub: github.com/TriodeGirl/ Arduino-Uno-R4-code-DAC-ADCints-Fast_Pins/ Summary The DAC is only one of the features of the R4 Minima that makes it so attractive. There’s the much larger flash memory, RAM and data EEPROM; the faster CPU with an inbuilt floating-point unit (FPU); the December 2023  27 inbuilt real-time clock (RTC); the inbuilt capacitive touch sensing unit; the inbuilt USB 2.0 full-speed comms module; an ADC with 14-bit resolution; and the inbuilt op amps and CAN port. We’ve only just scratched the surface of the Uno R4 Minima in this article. If you’d like to delve further, we suggest you get one and explore all its capabilities yourself. It really is a big step forward in the Arduinosphere! Where you can get it You can buy the Arduino Uno R4 Minima directly from the main Arduino website, but it’s also available from several suppliers on eBay. In most cases the cost will be around US$20, possibly with shipping costs added. WiFi version One last thing: the Uno R4 Minima isn’t the only new addition to the Arduino Uno family. It also has a sibling, the Uno R4 WiFi. That one has all the new features of the R4 Minima plus more: the addition of an Espressif ESP32-S3 to provide WiFi and Bluetooth comms, plus an onboard 12×8 LED matrix and a While we’ve reviewed the Uno R4 Minima (shown enlarged), there’s also a WiFi version of the board, see: https://store.arduino.cc/products/uno-r4-wifi SparkFun Qwiic I2C+power connector that can be used to plug in their add-on boards. As you’d expect, the Uno R4 WiFi costs more than the R4 Minima, at US$27.50. Still, those extra features are pretty tempting for an increase in cost of less than 50%, especially if you want wireless communications SC and networking. Silicon Chip as PDFs on USB ¯ A treasure trove of Silicon Chip magazines on a 32GB custom-made USB. ¯ Each USB is filled with a set of issues as PDFs – fully searchable and with a separate index – you just need a PDF viewer. ¯ 10% off your order (not including postage cost) if you are currently subscribed to the magazine. ¯ Receive an extra discount If you already own digital copies of the magazine (in the block you are ordering). The USB also comes with its own case EACH BLOCK OF ISSUES COSTS $100 OR PAY $500 FOR ALL SIX (+POSTAGE) NOVEMBER 1987 – DECEMBER 1994 JANUARY 1995 – DECEMBER 1999 JANUARY 2000 – DECEMBER 2004 JANUARY 2005 – DECEMBER 2009 JANUARY 2010 – DECEMBER 2014 JANUARY 2015 – DECEMBER 2019 WWW.SILICONCHIP.COM.AU/SHOP/DIGITAL_PDFS Ordering the USB also provides you with download access for the relevant PDFs, once your order has been processed 28 Silicon Chip Australia's electronics magazine siliconchip.com.au