Xerox Alto restoration, IC reverse engineering, chargers, and whatever I'm not really on many forums for arduino, but maybe I'll post it somewhere on my web site, and share a link wherever its allowed. The waveform generation mode bits WGM are set to to 001 for phase-correct PWM. Thanks Ken. Secrets of Arduino PWM.
Briefly, a PWM signal is a digital square wave, where the frequency is constant, but that fraction of the time the signal is on (the duty cycle) can be varied between 0 and 100%. But personally I'd just use PWM, at least to try it out and get the candle simulation algorithm working. To get 250kHz from a 16MHz clock, set OCRnA to count to 64 (to divide by 64), and then change OCRnB to get the duty cycle you want. To summarize the register settings, setting the waveform generation mode bits WGM to 011 selects fast PWM. dafaddah, that sounds very interesting; I'd like to see what you can do to "sculpt" a signal shape, so would you mind sharing a link here when you are done, so others can see your work? Timer 1 is a 16-bit timer and has additional modes. Colin, thanks for your comment.
Ken, thanks for this usefull document. analogWrite(127) means a signal of 50% duty cycle. The other bits are the same as for fast PWM. Very helpful. The answer is that analogWrite "cheats"; it has special-case code to explicitly turn off the pin when called on Timer 0 with a duty cycle of 0.
(Note that despite the function name, the output is a digital signal, often referred to as a square wave.) In this mode, the timer counts from 0 to OCRA (the value of output compare register A), rather than from 0 to 255. Hey, thanks for the great article. 100 us on/1000us total period = 10% at 1ms period, or 1khz. One major disadvantage is that any interrupts will affect the timing, which can cause considerable jitter unless you disable interrupts. Timer 2 has different prescaler values.
The analogWrite function provides a simple interface to the hardware PWM, but doesn't provide any control over frequency. Given the speed of the PWM, I expect any glitches due to updates would be invisible. Is it at least possible to stuff the count limit register without re-initializing the whole count sequence? The duty cycle will be a multiple of 33%, since the output can be high for 0, 2, 4, or 6 of the 6 cycles. Based on your experience with the execution speed of the Nano boards, what if the above described candle simulation did not have the benefit of a built in hardware aided PWM functionality. In the following diagram, the timer resets when it matches OCRnA, yielding a faster output frequency for OCnB than in the previous diagrams. Note that fast PWM holds the output high one cycle longer than the compare register value. I can't seem to get it to work
The Arduino uses Timer 0 internally for the millis() and delay() functions, so be warned that changing the frequency of this timer will cause those functions to be erroneous.
Very helpful, thanks--we're trying to use Arduinos to power a small pump and measure flow for an open source river modeling system, and I was hung on this topic until reading this--see our stuff at lrrd.blogspot.com. Timer Registers
by Ken Shirriff with further editing by Paul Badger the original document Pulse-width modulation (PWM) can be implemented on the Arduino in several ways. This article explains simple PWM techniques, as well as how to use the PWM registers directly for more control over the duty cycle and frequency. Each timer has two output compare registers that control the PWM width for the timer's two outputs: when the timer reaches the compare register value, the corresponding output is toggled.
But for maximum smooth transitions, I think I'll need to ensure that changes to the PWM limit counter (or counters depending on the method I guess) happen at predictable times, like when the counter reaches its limit, or when it returns to zero. Timer 1 is a 16-bit timer and has additional modes. The second important timing difference is that fast PWM holds the output high for one cycle longer than the output compare register value. Pulse-width modulation (PWM) can be implemented on the Arduino in several ways.
Timers and the Arduino Thomas May 3, 2018 - Pulse-width modulation (PWM) can be implemented on the Arduino in several ways. However, there is a special-case mode "Toggle OCnA on Compare Match" that will toggle output A at the end of each cycle, generating a fixed 50% duty cycle and half frequency in this case. The Arduino's programming language makes PWM easy to use; simply call analogWrite(pin, dutyCycle), where dutyCycle is a value from 0 to 255, and pin is one of the PWM pins (3, 5, 6, 9, 10, or 11). Secrets of Arduino PWM Pulse-width modulation (PWM) can be implemented on the Arduino in several ways. The timers can also generate interrupts on overflow and/or match against either output compare register, but that's beyond the scope of this article.
This article explains simple PWM techniques, as well as how to use the PWM registers directly for more control over the … Thus, the frequency will be divided by 4, not 3. The Arduino IDE has a built in function “analogWrite()” which can be used to generate a PWM signal. That way my main loop could simply adjust "brightness" variables, and I would know that changes to the timer register always happen at a predictable point in time.
I would need around 250 kHz with adjustable duty cycle on pin 9. There is literature on soft swtiching so the shape is more angled instead of hard edges but is there any benefit of the a curved shape. Looks like you need to do a closer read. As a consequency, the duty cycle of 1/256 is unavailable when you use analogWrite on Timer0, and there is a jump in the actual duty cycle between values of 0 and 1. In this mode, the timer counts from 0 to 255 and then back down to 0.
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