In this post I have explained how to generate sine wave pulse-width-modulation or SPWM through Arduino, which can be used for making a pure sine wave inverter circuit or similar gadgets.
The Arduino code is developed by me, and it is my first Arduino code, ...and it looks pretty good 🙂
What is SPWM
I have already explained how to generate SPWM using opamps in one of my earlier articles, you could go through it for understanding how it can be created using discrete components and regarding its importance.
Basically, SPWM which stands for sine wave pulse width modulation, is a type of pulse modulation where the pulses are modulated to simulate a sinusoidal waveform, so that the modulation is able to attain properties of a pure sine wave.
To implement a SPWM the pulses are modulated with an initial narrower widths which gradually get broader at the center of the cycle, and finally end being narrower at the end to finish the cycle.
To be more precise, the pulses begin with narrowest widths which gradually get broader with each subsequent pulses, and gets broadest at the center pulse, after this, the sequence continues on but with an opposite modulation, that is the pulses now gradually begin getting narrower until the cycle finishes.
Video Demo
This constitutes one SPWM cycle, and this repeats throughout at a particular rate as determined by the application frequency (usually 50Hz or 60Hz). Typically, SPWM is used for driving power devices such as mosfets or BJTs in inverters or converters.
This special modulation pattern ensures that the frequency cycles are executed with a gradually changing average voltage value (also called the RMS value) , instead of throwing sudden Hi/low voltage spikes as normally witnessed in flat square wave cycles.
This gradually modifying PWMs in a SPWM is purposely enforced so that it closely replicates the exponentially rising/falling pattern of a standard sinewaves or sinusoidal waveform, hence the name sinewave PWM or SPWM.
UPDATE: Get this Improved Arduino SPWM Code
Generating SPWM with Arduino
The above explained SPWM can be easily implemented using a few discrete parts, and also using Arduino which will probably enable you to get more accuracy with the waveform periods.
The following Arduino code can be used for implementing the intended SPWM for a given application.
Gosh!! that looks awfully big, if you know how to shorten it, you may certainly feel free to do it at your end.
// By Swagatam (my first Arduino Code)
void setup(){
pinMode(8, OUTPUT);
pinMode(9, OUTPUT);
}
void loop(){
digitalWrite(8, HIGH);
delayMicroseconds(500);
digitalWrite(8, LOW);
delayMicroseconds(500);
digitalWrite(8, HIGH);
delayMicroseconds(750);
digitalWrite(8, LOW);
delayMicroseconds(500);
digitalWrite(8, HIGH);
delayMicroseconds(1250);
digitalWrite(8, LOW);
delayMicroseconds(500);
digitalWrite(8, HIGH);
delayMicroseconds(2000);
digitalWrite(8, LOW);
delayMicroseconds(500);
digitalWrite(8, HIGH);
delayMicroseconds(1250);
digitalWrite(8, LOW);
delayMicroseconds(500);
digitalWrite(8, HIGH);
delayMicroseconds(750);
digitalWrite(8, LOW);
delayMicroseconds(500);
digitalWrite(8, HIGH);
delayMicroseconds(500);
digitalWrite(8, LOW);
//......
digitalWrite(9, HIGH);
delayMicroseconds(500);
digitalWrite(9, LOW);
delayMicroseconds(500);
digitalWrite(9, HIGH);
delayMicroseconds(750);
digitalWrite(9, LOW);
delayMicroseconds(500);
digitalWrite(9, HIGH);
delayMicroseconds(1250);
digitalWrite(9, LOW);
delayMicroseconds(500);
digitalWrite(9, HIGH);
delayMicroseconds(2000);
digitalWrite(9, LOW);
delayMicroseconds(500);
digitalWrite(9, HIGH);
delayMicroseconds(1250);
digitalWrite(9, LOW);
delayMicroseconds(500);
digitalWrite(9, HIGH);
delayMicroseconds(750);
digitalWrite(9, LOW);
delayMicroseconds(500);
digitalWrite(9, HIGH);
delayMicroseconds(500);
digitalWrite(9, LOW);
}
//-------------------------------------//
How the Code Works
So here in this Arduino program, we are making SPWM which is sinusoidal pulse width modulation. We do this to create a kind of waveform that looks like a sine wave but is made using square pulses of different widths.
We start with the setup part like this:
void setup(){
pinMode(8, OUTPUT);
pinMode(9, OUTPUT);
}This above code is just saying to Arduino that pin 8 and pin 9 both will be output pins. We will send HIGH and LOW signals from them. This setup runs only one time when Arduino starts.
Then we move to the loop part. Loop means everything inside it will run again and again forever.
void loop(){Now inside this loop, first we start giving SPWM pulses from pin 8. The idea is to start with small pulses, increase them step by step to peak value and then reduce again to small.
We do this:
digitalWrite(8, HIGH);
delayMicroseconds(500);
digitalWrite(8, LOW);
delayMicroseconds(500);This gives a thin pulse of 500 microsecond ON and 500 microsecond OFF. It is like sine wave just starting from zero.
Then:
digitalWrite(8, HIGH);
delayMicroseconds(750);
digitalWrite(8, LOW);
delayMicroseconds(500);This one is fatter than before meaning sine wave is going higher.
Then:
digitalWrite(8, HIGH);
delayMicroseconds(1250);
digitalWrite(8, LOW);
delayMicroseconds(500);Now pulse is even more fat. So sine wave is now rising more.
Then this:
digitalWrite(8, HIGH);
delayMicroseconds(2000);
digitalWrite(8, LOW);
delayMicroseconds(500);This is the maximum peak pulse. So we are at top of sine wave.
After this we begin going down.
digitalWrite(8, HIGH);
delayMicroseconds(1250);
digitalWrite(8, LOW);
delayMicroseconds(500);Then:
digitalWrite(8, HIGH);
delayMicroseconds(750);
digitalWrite(8, LOW);
delayMicroseconds(500);And finally:
digitalWrite(8, HIGH);
delayMicroseconds(500);
digitalWrite(8, LOW);So this above series of HIGH and LOW signals from pin 8 makes one full sine cycle using pulse widths. This is one full SPWM cycle for pin 8.
Now we do the exact same thing for pin 9, like this:
digitalWrite(9, HIGH);
delayMicroseconds(500);
digitalWrite(9, LOW);
delayMicroseconds(500);
digitalWrite(9, HIGH);
delayMicroseconds(750);
digitalWrite(9, LOW);
delayMicroseconds(500);
digitalWrite(9, HIGH);
delayMicroseconds(1250);
digitalWrite(9, LOW);
delayMicroseconds(500);
digitalWrite(9, HIGH);
delayMicroseconds(2000);
digitalWrite(9, LOW);
delayMicroseconds(500);
digitalWrite(9, HIGH);
delayMicroseconds(1250);
digitalWrite(9, LOW);
delayMicroseconds(500);
digitalWrite(9, HIGH);
delayMicroseconds(750);
digitalWrite(9, LOW);
delayMicroseconds(500);
digitalWrite(9, HIGH);
delayMicroseconds(500);
digitalWrite(9, LOW);
}So finally, this whole thing is a simple way to generate sine wave shaped signals using Arduino and square wave pulses of changing width.
In the next post I'll explain how to use the above Arduino based SPWM generator to make a pure sinewave inverter circuit....keep reading!
The above SPWM code was further improved by Mr Atton for enhancing its performance, as given below:
/*
This code was based on Swagatam SPWM code with changes made to remove errors. Use this code as you would use any other Swagatam’s works.
Atton Risk 2017
*/
const int sPWMArray[] = {500,500,750,500,1250,500,2000,500,1250,500,750,500,500}; // This is the array with the SPWM values change them at will
const int sPWMArrayValues = 13; // You need this since C doesn’t give you the length of an Array
// The pins
const int sPWMpin1 = 10;
const int sPWMpin2 = 9;
// The pin switches
bool sPWMpin1Status = true;
bool sPWMpin2Status = true;
void setup()
{
pinMode(sPWMpin1, OUTPUT);
pinMode(sPWMpin2, OUTPUT);
}
void loop()
{
// Loop for pin 1
for(int i(0); i != sPWMArrayValues; i++)
{
if(sPWMpin1Status)
{
digitalWrite(sPWMpin1, HIGH);
delayMicroseconds(sPWMArray[i]);
sPWMpin1Status = false;
}
else
{
digitalWrite(sPWMpin1, LOW);
delayMicroseconds(sPWMArray[i]);
sPWMpin1Status = true;
}
}
// Loop for pin 2
for(int i(0); i != sPWMArrayValues; i++)
{
if(sPWMpin2Status)
{
digitalWrite(sPWMpin2, HIGH);
delayMicroseconds(sPWMArray[i]);
sPWMpin2Status = false;
}
else
{
digitalWrite(sPWMpin2, LOW);
delayMicroseconds(sPWMArray[i]);
sPWMpin2Status = true;
}
}
}
Comments
only the switching frequency is 30KHz. but the main output is 60Hz. as my appliances needed. i am using SPWM right now generated by arduino UNO.
yes i am having different codes. i am using interrupt. since arduino loop function is very slow. because it has other code executed because of translating the code. it will affect the code inside the loop like speed.
OK, but make sure the pillars on each waveform does not exceed 6, but anyway your issue is current(amp) related not waveform.
I never tried high current h bridge., maybe I will try to build a high current h bridge so that I can check the output if it is going well., will update after I build., thanks always for the help.,
there should not be more than 4 to 6 pillars on each waveform, as implemented in my SPWM, I think you are using some other code not the above one.
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high swatagam, could you help me designing an filter for this?
here is my spwm, i used arduino uno. could you try simulate?
switching freq is 31Khz
freq:60 Hz
Hi Isak, I am sorry I am not good at simulating circuits, since I mostly depend on my brain simulation for all my designs.
hi swatagam, i tried simulation but. the value of capacitor is verry big about 20uf.
how can is reduce it? see my simulation please
https://www.dropbox.com/s/5s1kt37dfs92flh/simulation.png?dl=0
its hard to tell weather i put a right caps because i don’t have oscilloscope. i tried this with 2.2uf and it can run the stand fan. but not at great speed. i think it is not smooth as i expect because trying to switch at low speed the fan turn at very low speed. tried to compare the output at the grid. it has a big difference.
i can use an 8v – 230v transformer since i have a high switching frequency. now i set it to 30KHz. voltage drop is not much the problem.. the transformer is just a salvage from old ups. my code can change amplitude so that i can stabilize the voltage output. i can also change the switching frequency while system is running. but the main problem is the filter for 230 out.
you mean to say instead of 50Hz or 60Hz you are using 30kHz for driving the fan? That’s highly not recommended, and moreover the current consumption is the main aspect, check your battery current it must fulfill the fan’s rated consumption.
your transformer output must produce an AC that matches your grid AC characteristic in every respect.
without a scope you cannot verify an inverter output, it is a must.
and the fan speed is more related to current and wattage from the trafo not the waveform…..please read this post for learning regarding voltage drop issues
https://www.homemade-circuits.com/2017/07/inverter-voltage-drop-issue-how-to-solve.html
Hi Isak, that looks misleading, that’s why I never depend on simulators….if you check it practically you will find that a much smaller capacitor doing the job perfectly, because the transformer secondary itself will act like a filter and to a great extent smoothen the waveform even without a capacitor…
by the way you can try putting a load in the simulation and check the effect
Made some changes and put it on paste bin to make things easy
https://pastebin.com/1sQAi9vr
could you please throw some light regarding how this modification would help to improve the performance of the PWM output, I am sure the readers will love to know about it.
// Some changes made by Atton Risk for Swagatam
const int sPWMArray[] = {500,500,750,500,1250,500,2000,500,1250,500,750,500,500}; // This is the array with the SPWM values change them at will
const int sPWMArrayValues = 13; // You need this since C doesn’t give you the length of an Array
// The pins
const int sPWMpin1 = 8;
const int sPWMpin2 = 9;
// The pin switches
bool sPWMpin1Status = true;
bool sPWMpin2Status = true;
void setup()
{
pinMode(sPWMpin1, OUTPUT);
pinMode(sPWMpin2, OUTPUT);
}
void loop()
{
// Loop for pin 1
for(int i(0); i != sPWMArrayValues; i++)
{
if(sPWMpin1Status)
{
digitalWrite(sPWMpin1, HIGH);
delayMicroseconds(sPWMArray[i]);
sPWMpin1Status = false;
}
else
{
digitalWrite(sPWMpin1, LOW);
delayMicroseconds(sPWMArray[i]);
sPWMpin1Status = true;
}
}
// Loop for pin 2
for(int i(0); i != sPWMArrayValues; i++)
{
if(sPWMpin1Status)
{
digitalWrite(sPWMpin1, HIGH);
delayMicroseconds(sPWMArray[i]);
sPWMpin1Status = false;
}
else
{
digitalWrite(sPWMpin1, LOW);
delayMicroseconds(sPWMArray[i]);
sPWMpin1Status = true;
}
}
}
sure we can!
No problem I hope we can work together in the future.
Thank you very much Atton, I hope the readers will benefit immensely from this information! I appreciate it a lot!
Halo sir.
I will try your code and the driver as pure sine wave inverter.
If I successful to make it, may I re-post this article?
at least for arduino code only.
Thank you.
Yogi S.
Hello Yoyo,
you can submit the details to me, I'll post it in the above article with your credentials in it, but if you use it for your own website then that could be a copyright violation….
Hi,
as per the given code pin8/9 will alternately produce SPWM pulses at the rate of 50Hz. The total delay periods across the two pins are calculated to produce 50Hz frequency
The SPWM waveform rate (delays) is arbitrarily set in the code, you can tweak it to create a different RMS value depending upon your transformers primary voltage rating.
alternatively the Arduino code could be further upgraded for responding to a feedback from the transformer output and for achieving an automatic RMS adjustment
Hi sir,
Its good to see you involving in arduino projects, I hope you will soon master in this field too 🙂
I would like to point some errors in the code:
1) we must not use pin 13 in arduino, unless we run out of pins, since it is always connected with LED, it will deviate our results. we can use other pins say 8 and 9.
2) we cannot use delay for less than 1ms and we can't use decimal place in delay function like delay(1.25); . Instead use delayMicroseconds(); for instance delayMicroseconds(500); for 500us and delayMicroseconds(1250); for 1.25ms. You may replace all delay with this function.
The above errors won't show up while compiling but, it affects our end result.
Regards
Thank you GR,
Although I hardly find time, I did this just to have some fun … 🙂
I will surely correct the above code as per your suggestions, as soon as possible..
I appreciate your help very much and I am sure the readers will also get an opportunity to learn from this discussion.
Thanks again, and keep up the good work!