![]() It tests if you want the pin fully on or off, and it uses a whole switch() expression and memory lookup to figure out which timer registers to write to-and all of this just so that you don’t have to look up the pin in the datasheet.” “The price paid for the Arduino pin/timer abstraction is that what we do in one or two lines of code, and two or three cycles of CPU time, the Arduino does in 50+ clock cycles. In Elliott William’s book, he has the following to say about analogWrite: This means testing can be performed quickly and easily without having to make a software change. Each of these frequencies can be easily changed in one command via software. It might benefit from a higher frequency such as 976Hz, 1.95kHz or 3.9kHz. For example, if you are attempting to power a DC motor with the 490Hz signal, the specific motor might not respond well to such a low-frequency signal. This is something “that is easily changed” and of great value. It also removes the flexibility of changing the frequency of the analogWrite signal. In this process, changing the software is easily performed. To make the change, we would want to power down the board, change the circuit then power the board back up. In this case, once we’ve attached something to a specific pin, its doubtful we’re going to make that change “on the fly”. In other words, flexibility is great when the element is something that can be easily changed, and you would want to have the greatest opportunity to make a change. Second, this flexibility provided has little value as it delivers flexibility to something (specific hardware pin) which isn’t easily changed. First, the code size is significant, almost 1K bytes of program space to deliver a PWM signal to any one of the 6 pins. The analogWrite function provides flexibility (any one of the 6 pins) at a cost of fixed frequency (490Hz) and code size (5 times the size of standard C code size for a similar signal on a fixed pin).Īs an engineer, I have issues with two aspects of analogWrite. The 6 pins (3,5,6,9,10,11) have a “~” next to its pin number on the Uno board. It will deliver the same frequency 490Hz on one of 6 pins with the stated duty cycle. The Arduino uses PWM for its analogWrite(pin, duty cycle) function. If the concept remains foreign to you, I recommend you read the noted sources above before going forward. PWM is valuable as it allows you to use less power to keep motors running or make LEDs bright. The change is called the “duty cycle”, it will range from 0-100%, and the high the number, the greater the voltage delivered. ![]() The idea is to modulate (or change) the width of a digital signal (a pulse) to deliver a varying amount of voltage. Pulse-width modulation (PWM) is a useful technique for controlling DC motor speeds, LED intensity and creating analog waveforms.
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