Why Arduinos are Slow

Clock Speed

First of all, you are only as fast as your clock (disregarding multi-core processors), which the Arduino Uno defaults to using a 16Mhz crystal. What that means is the ATmega microcontroller can execute up to 16 million instructions per second. Now, 16 million instructions per second may sound like a lot (and it is, sort of), but when you consider what all an Arduino needs to do to execute even simple operations, it really isn't that much. For many projects, the clock cycles are shared between things like calculations, I2C communication, reading and writing to pins and registers, and many more operations.

Even then, seemingly simple commands can take up quite a bit of clock cycles, such as setting a digital pin to high. This is one of the simplest IO operations you can perform on an Arduino, but it actually takes a very long time (over 50 clock cycles!) because of the amount of code used in the digitalWrite() method, which I'll address in the next section. So a faster clock would allow you to execute the instructions at a faster pace.

How to Speed up Arduino

To be clear, we aren't actually making Arduino faster, rather, we're making the code more efficient. I point out this distinction because using these tricks won't give us a faster clock (although we can speed up the clock, which I'll touch on later), it will just execute less code. This is an important distinction because having a faster clock provides us other benefits, like having more precise timers, faster communication, etc.

Also, keep in mind that by using the code below you're making some trade-offs. The programmers who developed Arduino weren't just lousy coders who couldn't write fast code, they consciously made the decision to add validations and safety checks to methods like digitalWrite() since it benefits their target customers. Just make sure you understand what can (and will) go wrong with these kinds of trade-offs.

Saving Power with Software

So far we've talked about how to reduce the power of the Arduino, but we haven't talked about why it uses the power it does. Inside the ATmega328P, lies a series of circuits that work together to offload work from the processor, and each of these draws some amount of power. The Arduino's analogWrite() function, for example, doesn't have the processor create a PWM signal by counting the clock cycles itself. Instead, the Arduino uses one of the built in timers to count clock cycles and send an interrupt request to the processor. From there, the processor stops what it's doing and handles the interrupt by switching the pin's state. By offloading some of the work, the microcontroller is able to do multiple things at the same time. Some of the other circuitry built into the ATmega328P include:

• 3 timers

• Watchdog timer

• Brown-out detect

• Analog to digital conversion

Each of these independent components need power to work, and, unless you manually disable them, they will continue to draw power. The brown-out detection actively monitors the system voltage to ensure it doesn't drop below its threshold. If it does, the controller powers down until the voltage is increased above that threshold. The analog to digital converter (ADC) does just as the name suggests, it take the analog voltage (which can be any value from 0V up to VCC) and converts it to a digital value that the microcontroller can use (0-1023 for 10-bit converters). If your project doesn't need to use the ADC, disabling it will cut down on the power draw drastically.

But what if you still need the ADC? Thankfully there are registers where you can disable some of these circuits with software. Using software allows you to enable the circuits you need, when you need them, and, when you're done, you can disable them again. All of the registers are well documented in the datasheet for the ATmega328p, but, if directly writing to registers makes you uncomfortable, there is a library available that you can download from the link below. For instructions on how to install an Arduino library

This library allows you to set how long to enter into sleep mode, from a few milliseconds, up to indefinitely. It also allows you to specify which parts of the micro to disable, making it a pretty powerful and versatile library for your low-power needs.