Colin Snow
The Arduino Nano is a compact, flexible, and user-friendly board. It has a variety of applications, including remote controls and processing rotary encoders. The Nano can be put into sleep mode, and there are several ways to wake it up, including using the Timer function, interrupts, or external wake-up events. The Jetson Nano also has a Deep Sleep Mode (SC7) that can be activated.
Characteristics and Values Table
| Characteristics | Values |
|---|---|
| Sleep Mode | Low Power Mode, Power-Down Mode, Deep Sleep Mode(SC7) |
| Wake-Up Methods | Internal Interrupts, External Wake-Up Events, Timer Function, Multiple Buttons, SLEEP/WAKE* (pin_240) |
| Power Consumption | 50% reduction in average current in low power mode, resulting in almost double the battery life |
| Wake-Up Sources | Various, including timer overflow, UART transmission complete, and rotary encoder input |
| Wake-Up Delay | A delay is expected between the wake-up event and resuming normal mode to allow the clock to settle |
| Wake-Up Events | Can be configured and planned using the "LowPower" library and timer function |
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What You'll Learn
Arduino Nano sleep mode
Arduino boards are popular for electronics projects, but they can be quite power-hungry. The Arduino Uno, for example, can drain a 750mAh 3.7V LiPo battery in under 12 hours. This is where sleep mode comes in—it's a way to significantly reduce power consumption and extend the device's runtime.
Sleep modes are particularly useful for applications with intermittent tasks, such as sensors or real-time clock (RTC) modules. When an interrupt is required, the Arduino can be woken up to perform a specific task and then allowed to go back to sleep. This is especially relevant for portable electronics, where maximising battery life is crucial.
To put an Arduino into sleep mode, you can follow these general steps:
- Download and install a low-power library, such as the one provided by Rocketscream.
- Cut the power to the power LED.
- Remove the voltage regulator or reduce the system voltage (be careful not to reduce it too much, or the microcontroller may behave erratically).
- Upload the sleep mode code to the Arduino using the Arduino IDE.
- Check the current consumption with a USB ammeter or a clamp meter.
For an Arduino Nano specifically, you can use the Low-Power library from Rocketscream, cut the power to the power LED, and remove the voltage regulator. Additionally, you can reduce the clock speed to 8 MHz. Here's an example of the source code that puts the Arduino Nano into deep sleep:
Cpp
Void setup() {
CLKPR = 0x80; // (1000 0000) enable change in clock frequency
CLKPR = 0x01; // (0000 0001) use clock division factor 2 to reduce the frequency from 16 MHz to 8
}
Void loop() {
// Go to sleep until the next scheduled wake up
Int32_t waitSeconds = 60;
While (waitSeconds > 0) {
Period_t waitFor = SelectWaitTime(waitSeconds);
LowPower.powerDown(waitFor, ADC_OFF, BOD_OFF);
WaitSeconds -= PeriodToSeconds(waitFor);
}
}
Period_t SelectWaitTime(int32_t secondsToWait) {
If (secondsToWait >= 8) return SLEEP_8S;
Else if (secondsToWait >= 4
}
In this code, the Arduino Nano will go into a deep sleep until the next scheduled wake-up. The `setup` function configures the clock to allow for a change in frequency, and the `loop` function controls the sleep and wake-up behaviour. The `SelectWaitTime` function determines the appropriate sleep mode based on the remaining wait time.
By utilising sleep modes and power-saving techniques, you can significantly extend the battery life of your Arduino Nano projects and make them more efficient.
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Waking up an Arduino Nano
There are several ways to wake up an Arduino Nano from sleep mode, enabling you to create power-efficient and user-friendly projects. Firstly, it is important to understand the different sleep modes available and the various sources of wake-up events.
One way to wake up an Arduino Nano is by using the ""LowPower" library, which allows you to quickly put the device to sleep and configure the wake-up options. The Low Power library is available on GitHub, and you can download the zip file to add it to your project.
Another method is to use the Timer function, which is a synchronous wake-up event as you plan when to wake up the Arduino before putting it to sleep. This can be done by sending the first parameter as the time, for example, setting the parameter to 2 seconds.
Additionally, you can use external wake-up events, such as triggering a hardware interrupt. For example, you can use a DS3231 module, connecting the SDA to A4 and SCL to A5. Pins for hardware interrupts on the Nano are D2 and D3.
Furthermore, you can use a Real-Time Clock (RTC) to wake up the Arduino. This involves using a jumper wire in D2, waiting for the LED to turn off, and then inserting the other end of the jumper wire into a GND pin. This pulls pin 2 LOW, triggering the interrupt and waking up the Arduino.
By understanding the different sleep modes and wake-up sources, you can develop projects that are responsive and battery-friendly.
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Using the LowPower library
The LowPower library is a popular option for those looking to save power on their microcontrollers. It is a lightweight library that can be used to put an Arduino Nano into a low-power sleep mode, reducing power consumption to less than 0.05 mA.
To use the LowPower library, you can follow these steps:
- Install the LowPower library: Search for the LowPower library in the library manager of your Arduino IDE and install it. Alternatively, you can download the library from the Rocket Scream website and install it manually.
- Include the Library: In your Arduino sketch, include the LowPower library at the beginning of your code. You can do this by adding the following line: `#include
` - Set Up the Sleep Mode: In your setup function, you can enable the sleep mode by reducing the clock speed and configuring the sleep duration. Here's an example code snippet:
Cpp
Void setup()
{
CLKPR = 0x80; // Enable change in clock frequency
CLKPR = 0x01; // Use clock division factor 2 to reduce frequency from 16 MHz to 8 MHz
// Configure wake-up duration (e.g., sleep for 60 seconds)
Int32_t waitSeconds = 60;
}
Enter Sleep Mode: In your loop function, you can use the LowPower.powerDown() function to enter the low-power sleep mode until the next scheduled wake-up. Here's an example:
Cpp
Void loop()
{
While (waitSeconds > 0)
{
Period_t waitFor = SelectWaitTime(waitSeconds);
LowPower.powerDown(waitFor, ADC_OFF, BOD_OFF);
WaitSeconds -= PeriodToSeconds(waitFor);
}
}
Select Wait Time: Implement a function to select the wait time based on the remaining `waitSeconds`. You can use different sleep modes, such as SLEEP_1S, SLEEP_2S, SLEEP_4S, or SLEEP_8S. Here's an example:
Cpp
Period_t SelectWaitTime(int32_t secondsToWait)
{
If (secondsToWait >= 8) return SLEEP_8S;
Else if (secondsToWait >= 4) return SLEEP_4S;
Else if (secondsToWait >= 2) return SLEEP_2S;
Else if (secondsToWait >= 1) return SLEEP_1S;
}
Additional Considerations: Depending on your specific use case, you may need to consider other factors such as interrupts, sensors, and external peripherals. You can refer to the Rocket Scream documentation for more details on these considerations.
By following these steps, you can effectively use the LowPower library to put your Arduino Nano into a low-power sleep mode, reducing power consumption and extending battery life.
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Power-saving benefits
Arduino boards are versatile and can be used in a variety of power-saving projects. The Arduino Nano, in particular, has several features that contribute to its power-saving benefits.
Firstly, the Nano offers different power modes, including a Deep Sleep Mode (SC7), that can be utilised to reduce power consumption. When in low-power mode, the current consumption is significantly reduced, leading to a longer battery life. This makes it ideal for projects that require responsiveness while being battery-friendly.
Additionally, the Nano provides flexibility in terms of wake-up sources. It can be configured to wake up from sleep mode through various internal and external events, such as timer interrupts, UART transmission completion, or user interactions. This allows for efficient power management by planning when the Nano should wake up and only consuming power when necessary.
The Nano also supports the use of the "LowPower" library, which facilitates easy implementation of sleep and wake-up configurations. With this library, developers can quickly put the Nano to sleep and set the desired wake-up options, making it convenient to create power-efficient projects.
Furthermore, the Nano's ability to handle interrupts is advantageous for power-saving. While the concern about only having two interrupt-capable pins is common, it's a myth. All pins can handle interrupts, known as pin change interrupts, with certain limitations. This enables developers to design projects that efficiently respond to events while conserving power.
Overall, the Arduino Nano's various power modes, configurable wake-up sources, library support, and interrupt handling capabilities make it a powerful tool for creating projects that optimise power efficiency and extend battery life.
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Deep Sleep Mode (SC7)
Deep Sleep Mode, also known as SC7, is a feature available on certain devices such as the Jetson AGX Orin 64GB and the Jetson TX2. This mode allows the device to enter a state of low power consumption, reducing the average current by about 50% and resulting in longer battery life.
To enable Deep Sleep Mode on a device, one can refer to the MCU datasheet to understand the specific methods available for the particular MCU. In some cases, the SM [2:0] in the SMCR (Sleep Mode Control) register can be used to set the device into one of the power modes. Additionally, the "LowPower" library can be installed to quickly put the device into sleep mode and configure the wake-up options.
It is important to note that there may be a delay between the wake-up event and resuming normal mode, as the clock needs to settle. Different wake-up sources, such as internal interrupts or external events, can be utilized to wake the device from Deep Sleep Mode.
While Deep Sleep Mode offers significant power savings, it is not without its challenges. Some users have reported issues with Deep Sleep Mode (SC7) not working properly on certain platforms, such as the Jetson Nano eMMC. In such cases, physical intervention, such as a restart, may be required to restore the device's connection.
Overall, Deep Sleep Mode (SC7) is a valuable feature for power-efficient projects, enabling devices to conserve energy while remaining responsive to wake-up events.
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Frequently asked questions
Using the “LowPower” library, you can quickly put an Arduino Nano to sleep and wake it up by configuring the wake-up options accordingly.
The Low Power library is available on GitHub. You can download the zip file from there and add it to your project by going to Sketch → Include Library → Low-Power (under the contributed library section).
Some sources of wake-up events for an Arduino Nano include timer overflow, UART transmission complete, and external events like button presses or sensor readings.
You can configure the wake-up options by using the SM [2:0] in the SMCR (sleep mode control) register. This allows you to set the Arduino Nano into one of the power modes.
Yes, by using the sleep mode, you can reduce the current consumption of the MCU and almost double the battery life. Additionally, using the timer function can help plan the wake-up event and further reduce power consumption.
