Which Microcontrollers Can Take the Heat?

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IoT implementations continue to be integrated into our world in the billions, collecting data in a wide variety of situations. In some scenarios, we may need to think about which systems can stand up to hot environments, such as inside of a car’s engine compartment, agricultural sensors, in the controls of appliances that get hot like ovens or dishwashers, or to monitor batteries and solar cells in a home power generation setup.

High Temperature Microcontrollers

In order to determine which systems can take the heat, I tested a variety of readily available development boards under extreme heat conditions, including a genuine Arduino Uno and 3 Arduino Nano clones, both featuring ATmega328P microcontrollers; an Adafruit Huzzah with an ESP8266 WiFi module; and a Sparkfun Micro with an ATmega32U4 microcontroller. Along with this, a Raspberry Pi 3 featuring a quad Core Broadcom BCM2837 CPU and a Raspberry Pi Zero with a single-core Broadcom BCM2836 processor single board computers were tested.

0918_microconroller_1 - most boards tested on display 

These boards represent a sampling of available options for prototype/DIY use, and the underlying chips and architecture can be applied to designs meant for mass production.

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Test Setup

 0918_microconroller_4 - Raspberry Pi ready for test

In order to see which of these boards/chips can withstand high temperatures, each was placed inside of a toaster oven preheated to 150, 200 and 250°F for five minutes. Each board was programmed to blink an LED—or two alternating LEDs in the case of the Pro Micro—and observed to see when blinking stopped, indicating a breakdown in the board. Power was provided by a USB cable routed in between the oven door and the body of the oven.

These temperatures were chosen for the tests, as at 250 degrees the connectors began to show significant signs of deformation, raising questions about human safety and ruling out long-term use unless specialized connectors were used. Given that the Raspberry Pi throttles back performance once it hits 185°F, and that the ATmega328P’s temperature rating is between -40 and 85°C—185°F—this seemed like a reasonable temperature range that would be expected to cause failures.

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Test Results

0918_microconroller_3 - Huzzah board in experiment 

Surprisingly, even though the temperature of each was pushed well beyond the limit of what these chips were rated for, each kept their respective LED blinking throughout the entire test. One might suspect, and perhaps with some validity, that these boards/chips never reached the oven temperatures in the five minutes that they were tested. Chips, however, are designed to dissipate heat to the environment, and each board tested is quite thin, suggesting that they were indeed quite hot internally. They were also observed to be hot to the touch.

While you might not want to use something like this in an oven, it seems that this type of board can endure short-term bursts of heat. In the long term, one would certainly want to stick to manufacturer ratings, especially in more taxing applications were the processor is generating more of its own thermal energy. However, in some carefully designed applications where the chip/board and connectors are considered disposable—scientific experiments come to mind—this short-term heat capacity can come in quite handy.

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Microcontroller Board Comparison

0918_microconroller_4 - Arduino Nano after destruction 

While these results were surprising—I didn’t expect for every one of them to be able to stand up to temperatures well beyond what they were rated for a significant amount of time—at some point these boards will shut down or simply burn up. To find this limit, I initially pre-heated the toaster oven to 450°F. During this experiment I’d been using a piece of plywood inside the oven to keep from having to set the boards on the conductive metal surfaces, which started smoking violently. Fearing combustion, this temperature setting was decreased to 350°F. This decreased the smoke considerably, appearing to be water vapor from the plywood.

After a brief pre-heat, I inserted a blinking Arduino Nano clone into the oven, fully expecting it to stop blinking within the normally allotted five minutes. When this time had passed, the onboard LED was still dutifully blinking away. Given that it was an environment 165°F higher than the microprocessor’s rated temperature, this was truly surprising, and this temperature was at the limits of what I was comfortable with in my experimental setup.

Despite this impressive robustness, I decided to leave it in the oven for another five minutes. After nine minutes, I was preparing to record my results (blinking, as usual) when to my pleasant surprise it actually stopped blinking. The USB connection hardware had separated from the board, denying power to the chip and LED. Additionally, the USB cable providing power, while functional, was in a state of melting—not something one would trust with a critical process.

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While you should certainly stick to manufacturers’ recommendations when designing systems, it’s interesting to note that at least for short periods of time, these chips can stand up to an impressive amount of thermal abuse. You wouldn’t want to put a chip directly inside your IoT oven, but with a proper thermocouple setup and an appropriate amount of insulation, the microcontroller on the outside of the heated area should fare quite well.

 

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