5/6/2021 0 Comments Pwm Current Control
Cool overview of different technologies for current measurements. (In my example here, I am using a Shunt Resistor.).When measuring the voltage or current of a PWM signal, there are unique challenges.You can use this tutorial to measure PWM current with a modified moving average (MMA).
In the meantime, one choice I made was to include an INA219 current sensor on the LED power supply. For prototyping, Im using the Adafruit Breakout Board, but my final design uses the same parts integrated into a custom PCB. Its fast, and its precise. Isnt that a good thing) The way it works is by measuring the voltage drop across a precision shunt resistor that the load current flows through. However, it is much faster than I expected and was providing (nearly) instant answers. So each time I checked the sensor, I got a seemingly random value. Id get the high current, low current (none), or a transition. Plus, it was taking up hundreds of bytes of RAM just to get an idea of the RMS current used in my design. This simple algorithm uses only a few bytes of RAM and is more accurate than a simple averaging algorithm. Plus if youre using a slower processor, like the Unos ATmega328p this method uses much less floating point. This article explains other types of moving averages.). Obviously, the number of samples can be a constant, saving a byte or two of memory. The previous measurements summed together, with a slight twice. This math is the most time-consuming step since division is involved. If you didnt know, most processors dont know how to divide.). Get a new sample and add that to the sum, replacing the average you just removed. The best part is that if you increase the number of samples used for the sum, neither the RAM nor the calculation time changes. Pwm Current Control Code Took AboutBefore I moved to the ESP8266, this code took about 56us to execute on an Uno. That speed is fast enough; it has little impact on the programs performance. You can download the Simple Average Example Here and grab the MMA example from both. You just need PWM and Analog In pins. Be careful on ESP8266s, since the maximum Analog In is only 1 volt.) In my test, I used an Uno and inserted a wire from digital pin 5 to analog pin A0. Second, it uses less RAM., And I see far fewer fluctuations in the average value. The trade-off, of course, can be that if you are looking for any random or instantaneous glitches, theyll be smoothed out. When calculating power, this is helpful because you dont need to include time in your math. ![]() Cool overview of different technologies for current measurements. In my example here, I am using a Shunt Resistor.).
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