What is the Arduino R4 Minima?
The Arduino R4 Minima is the latest version of the cherished Arduino UNO, with roots in education dating back to 2010 with the introduction of the original UNO. The greatest difference between the original UNO and the latest R4 is the switch to a Renesas RA4M1 as opposed to the original Atmel (Microchip) ATmega328. The new 32-bit processor offers a considerable performance improvement over the older 8-bit solution. It also integrates supporting hardware, eliminating the need for the crystal oscillator and the secondary microcontroller used to program the primary microcontroller. The resulting design lives up to its minimalist name as the board is considerably less cluttered when compared to an older UNO R2 as shown in Figure 1.
The latest edition of the Arduino UNO features the same form factor as the original UNO. This, coupled with a 5 VDC I/O, should allow continued use of your 5 VDC shields. The latest (Revision 4) Arduino UNOs are available with a LED matrix and WIFI (not shown) and without ABX00080 (Figure 1, left).
Figure 1: Side by side comparison of the latest Arduino UNO R4 Minima (left) and an older Arduino UNO R2 (right). The older R2 is easily identified by the placement of the reset button next to the microcontroller.
Tech Tip: Pay close attention to the voltages associated with your Arduino. The original devices were designed with 5 VDC microcontrollers. Many, but not all, of the new devices feature 3.3 VDC microcontrollers. Mixing the two systems could result in a damaged microcontroller. The Arduino R4 Minima is a 5 VDC device.
Power supply
The power supply for the new Arduino UNO R4 is an underappreciated change when compared to the earlier devices. Instead of using a traditional Low Drop Out (LDO) linear regulator, the R4 incorporates a switch mode power supply based on the Renesas ISL854102FRZ-T buck regulator.
Benefits of the switched mode regulator
Efficiency is the single best word used to describe the benefit of the switched mode power supply. Recall that a switch mode supply such as the ISL854102FRZ-T buck regulator operates by rapidly turning a semiconductor on and off. When combined with an inductor and capacitor, the high frequency on/off signal is converted into a steady DC level. The result is a system that is approximately 90% efficient. With greater efficiency, less energy is wasted as heat resulting in long battery life and a cool operation.
Test to demonstrate the improved thermal performance
The practical difference between the regulators may be observed by placing the regulator under load and then viewing the results with a thermal imager. For this demonstration, the Arduino was driven by an external 10 VDC supply. A 20 Ω resistive load was then placed on the regulator’s 5 VDC output as shown in Figure 2. The results are captured in Figures 3 and 4.
Figure 2: Test setup for the power supply thermal image. The Arduino is driven by an external 10 VDC supply. The 5 VDC regulator is used to drive a pair of series-connected 10 Ω resistors.
Results for the Arduino UNO R2
Figure 3 shows the thermal signature for the Arduino UNO R2. The linear regulator has an operating temperature of about 200°F as seen by comparing the color to the scale on the right-hand side of the image. This is very hot relative to the remainder of the PCB as seen on the color scale. The regulator is a brilliant yellow while the remainder of the board is a cool black.
Recall that a linear regulator functions like an adjustable variable resistor where input current is equal to output current. With a 10 VDC input, a 5 VDC output, and 0.25 A current flow (5 A / 20 Ω), the regulator will consume (burn) as much power as the load. Consequently, for the given configuration, the regulator is 50% efficient. The efficiency will decrease with rising input voltage.
Figure 3: Thermal image of the Arduino UNO R2 featuring a thermal regulator. The regulator has an operating temperature of about 200°F. It is significantly hotter than the remainder of the board.
Tech Tip: A “thermometer” is included on the right-hand side of Figures 3 and 4 allowing us to encode temperature as a color ranging from “yellow hot” to black. Note that the scales for Figure 3 and Figure 4 are not the same. Had the same scale been used for both thermal images, the UNO R4 Minima would have been black, similar to the cool black parts of Figure 3. You can confirm this by observing the highest temperature in Figure 4 is about 100°F, which is just above black using the Figure 3 color scale.
Results for the Arduino UNO Minima
This cool operation of the Arduino R4 Minima is shown in Figure 4. The regulator section of the PCB is about 100° cooler while delivering the same power to the dummy load. This is consistent with the Renesas ISL854102FRZ-T datasheet, which suggests 90% efficiency.
As explained in the previous tech tip, the color scales are different between Figures 3 and 4. One way to understand the difference is to observe the relative difference between the hottest and the coolest part of the board. In Figure 3, the “thermometer” measures between 225° and 80° F corresponding to the yellow hot spot on the regulator and the cool black on the right-hand side of the PCB. In Figure 4, the “thermometer” measures between 106° and 77° F. The ISL854102FRZ-T regulator is hot, but not significantly hotter than the remainder of the PCB. From a relative perspective, it is not that much hotter than the microprocessor or the LEDs.
Figure 4: Thermal image of the Arduino R4 Minima featuring a switch mode power supply. The switching regulator operates about 100°F cooler than the linear regulator. In fact, it is not that much hotter than the remainder of the board as evident by the orange hue across the entire image. Note that this image would be nearly black (cold) if the “thermometer” from Figure 3 were used.
Tech Tip: While the linear regulator is less efficient, it is still a viable solution. There is a good argument to be made for design simplicity. Also, the linear regulator is less prone to generate electrical noise and give off RF energy. This can further simplify the PCB design and reduce the complexity of EMI compliance. As an example, the linear regulator is preferred for circuits involving low noise signal amplification.
Parting thoughts
The Arduino UNO R4 Minima is a significant upgrade to the R3. The power supply explored in this article is but one of many changes included in the upgrade. The thermal images in Figure 3 and 4 provide a crystal-clear demonstration of the advantage associated with the new technology.
Please leave your comments and suggestions in the space below. Let us know if you have any questions about Arduino products.
Best wishes,
APDahlen
Helpful links
Please follow these links to related and useful information:
- Digikey’s product selection guides
- Arduino education content
- UNO R4 Minima Documentation
- UNO R4 Schematic
About this author
Aaron Dahlen, LCDR USCG (Ret.), serves as an application engineer at DigiKey. He has a unique electronics and automation foundation built over a 27-year military career as a technician and engineer which was further enhanced by 12 years of teaching (partially interwoven with military experience). With an MSEE degree from Minnesota State University, Mankato, Dahlen has taught in an ABET-accredited EE program, served as the program coordinator for an EET program, and taught component-level repair to military electronics technicians. Dahlen has returned to his Northern Minnesota home and thoroughly enjoys researching and writing educational articles about electronics and automation.
Highlighted Experience
Dahlen is an active contributor to the DigiKey TechForum. At the time of this writing, he has created over 170 unique posts and provided an additional 570 forum posts. Dahlen shares his insights on a wide variety of topics including microcontrollers, FPGA programming in Verilog, and a large body of work on industrial controls.
Questions
The following questions will help reinforce the content of the article.
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What is the purpose of the Arduino voltage regulator?
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What is the significance of the 5 VDC when compared to the 3.3 VDC I/O pin specification?
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Describe the operation of a switched mode power supply.
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Describe the operation of an LDO linear regulator.
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Locate the datasheet efficiency curves for the ISL854102FRZ-T buck regulator. Describe how the efficiency changes as the input voltage changes.
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Locate the schematic for the R4 WiFi and the schematic for the R4 Minima and then describe the difference in the power supply sections.
Critical thinking questions
These critical thinking questions expand the article’s content allowing you to develop a big picture understanding the material and its relationship to adjacent topics. They are often open ended, require research, and are best answered in essay form.
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What is the efficiency of a linear regulator operating with a 15 VDC input, a 5 VDC output, while delivering 1A?
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Sketch the block diagram for a buck regulator.
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Contrast and compare the losses in a linear regulator with the losses in a switch mode regulator.
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What is galvanic isolation? What impact will this have on your Arduino-based design?