![]() ![]() With these devices, the program must wait for synchronization to complete before it can move on to setting a value in another register. In this scheme there is only a single sync bit covering all the registers. Some modules use a common synchronization scheme. ![]() ![]() Moreover, the results of not synchronizing them varies from subsystem to subsystem.įurther, the SAM uses two broad synchronization mechanisms. Not all registers need to be synchronized in all cases. One added complexity of the SAM based Arduinos is the need to synchronize registers between the various clock domains when changing them. The clock divider, N, in Equation 2, can be set to one of the following values: 1, 2, 4, 8, 16, 64, 256, and 1024. Pages 660 and 661 of the Atmel datasheet for the SAMD21 provides the following two equations for SSPWM. In this example, the PWM system would generate a duty cycle of 50%. The output’s duty cycle is set by a second value ( CCx) that is between 0 and TOP which toggles the output.įor example, a TOP of 255 would provide an 8-bit resolution PWM, with the CCx counter set to 127, the output would be driven high while the counter is between 0 and 127, then pulled low until the counter resets to 0. Single-slope PWM on the SAM21 is set’s its frequency by incrementing counter once every clock cycle counting from 0 to a user-defined TOP value. However, the methodology is the same for other PWM modes, only you’ll need to adjust the equations. Generally speaking though, the PWM problem starts with knowing the PWM frequency and an a minimum resolution, and having to work backwards to to figure out the dividers that the system will use.įor this article I’ll be working with the single-slope PWM mode, as that’s what I’m using in LED light panel controller project. However, for photographic lighting, which was the project that got me started down this path, the resolution translates to a wider controllable range. In many applications the higher resolution isn’t that importantly. A SAM based Arduino can run at the same frequency but provide just under 11 bits of resolution using the 48 MHz clock, and just under 12 bits of resolution at 96 MHz. This allows for better PWM resolution while maintaining a high frequency.įor example, an AVR based Arduino Uno could do a 25 KHz PWM on it’s timer 1 output, and so with just over 9-bits worth of resolution. When it comes to PWM, the biggest advantage that the SAM21 based Arduinos over the AVR ones is that they have a much faster clocks, as fast as 96 MHz, available to run the counters with. Calculating a PWM Frequency and Resolution The code presented in this article was testing on a MKR WiFi 1010 and compiled using version 1.8.8 of the Arduino development environment. This applies to most if not all current SAM D21 based Arduinos including: This way I could integrate it into my home automation/light control system and control the bias lights from my computer, such as turning them on with the computer. As it was an inexpensive way to get a Wi-Fi network enabled device to control my lighting system. Simultaneously, as part of the bias lighting project, I also started working with the Arduino MKR WiFi 1010. However, earlier this year when looking into LEDs for bias lighting my workstation, I ran across an article by Waveform Lighting, that talked about using a 25 KHz PWM frequency to produce flicker free lighting for video use. I did know that PWM could be used, as there are LED systems that use it and don’t flicker, but I wasn’t completely clear on how they were accomplishing that. Both of these methods have their trade-offs, with PWM being slightly easier to implement, as most micro controllers have PWM generators built in, but hash the downsize of strobing the lights. Dimming LEDs can be done either by using a constant current power supply and controlling the current through the LEDs, or with pulse width modulation (PWM). However, I ran into issues flicker due to the relatively low PWM frequency.Īt the time, I didn’t have an effective solution to this problem. At the time I my intent was to use the AVR based Arduino Uno and it’s PWM engine. The impetus for this project goes back to 2015 when I started looking into building a DiY LED lighting system for video and photography applications. This guide covers the basics of configuring and using the built in PWM generator of the Atmel SAM D21 micro-controller that’s used in certain Arduino devices, like the MKR WIFI 1010. High-frequency PWM is a necessity for some applications, like flicker free video lighting and interfacing with certain types of 4-wire PWM controlled fans. Configuring the Timer Counter for Control Applications module.Calculating a PWM Frequency and Resolution. ![]()
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