sinusoidal PWM

[bwaxing]

Hi there,i'm new to this forum,m learning the PIC BASIC PRO programming and now i want to generate a sinusoidal pulse width modulated signal by using pic16f877 microcontroller,please i need some ideas on how to go about it and code example to start with....

[ScaleRobotics]

Hello and welcome to the forum.

Microchip has an application note for sine wave with the 16F series chip. They show two ways to do it, one with PWM and the next with a resistor ladder. http://ww1.microchip.com/downloads/e...tes/00655a.pdf

The PIC18F2431 and PIC18F4431 have some great features for multi pwm sine waves. So recently most of the examples use this chip.

Here are a few examples: http://www.picbasic.co.uk/forum/cont...-DT-interrupts

http://www.picbasic.co.uk/forum/showthread.php?t=14359

You can also enter a search for sine and get some more.

[bwaxing]

thanx..m working on them

[bwaxing]

Hi,i've read the Microchip appliction notes for sine wave with the 16F series chip..http://ww1.microchip.com/downloads/en/AppNotes/00655a.pdf together with the examples given in http://www.picbasic.co.uk/forum/content.php?r=229-Sine-wave-using-DT- interrupts and http://www.picbasic.co.uk/forum/showthread.php?t=14359.

there are number of things which i've not understand from these readings and i'm asking for help from anyone who can help me to understand.these things are:
1)how to generate a lookup table for the sine waveforms
2)how to include DT_INTS-18.bas file so that when i compile,the compiler will be able to open it
3)what is the purpose of this piece of code from example of http://www.picbasic.co.uk/forum/cont...-DT-interrupts

asm
__CONFIG _CONFIG1H, _OSC_HSPLL_1H
__CONFIG _CONFIG2H, _WDTEN_OFF_2H & _WDPS_512_2H
__CONFIG _CONFIG4L, _LVP_OFF_4L
endasm

thank you in advance.

[ronsimpson]

1) You could use the 32 location array you pointed at in question 3. I used M.S. EXCEL.
3) Get the data sheet for the PIC in PDF format and search for _OSC_HSPLL_1H or some piece of that. In the first of the 3 you can see these bits setup the oscillator and PLL. Most of the PICs have many modes for the oscillator. Internal/ external, divide by 32/ multiply by 4, etc.

1)how to generate a lookup table for the sine waveforms
2)how to include DT_INTS-18.bas file so that when i compile,the compiler will be able to open it
3)what is the purpose of this piece of code from example of http://www.picbasic.co.uk/forum/cont...-DT-interrupts

asm
__CONFIG _CONFIG1H, _OSC_HSPLL_1H
__CONFIG _CONFIG2H, _WDTEN_OFF_2H & _WDPS_512_2H
__CONFIG _CONFIG4L, _LVP_OFF_4L
endasm

thank you in advance.[/QUOTE]

[pxidr84]

to bwaxing:

My advice : read this great post with exemples, the sine is stored in an array :
http://www.picbasic.co.uk/forum/cont...-DT-interrupts

[bwaxing]

thanks for the advice,i read examples from that post and I've not understand how to create the lookup table.From that post sine is stored in the array and i don't understand how the value for a particular step have been determined.for example i want to use 8-bit resolutions (256 steps),how will i determine the value of each step?is there a formula or something?
thanks again.

[ScaleRobotics]

The max I see most people do is a 72 step lookup or array. (36 or 72 steps makes it easier to off set for multiple phases). The resistor capacitor filter smooths out the steps. It is still 8 bit resolution, even with 32 or 36 steps. If you wanted to have each value be more accurate, you could use 10 bits in your values for each step.

[bwaxing]

Hi,
thanks for the tip,m trying to modify the example you gave in http://www.picbasic.co.uk/forum/cont...-DT-interrupts so that i can generate a 50Hz sinusoidal PWM signal to control a single phase inverter using pic16f877.If i understand u correctly,in the sine array you jumped four steps to get 128 steps of 8-bit resolution,but how you got the correspond value for each step is not clear to me,i want to learn how to create a lookup table the way you did as i dont know how to create it using excel.what formula was used to get these values from that example?
; Set sine "table" in an array
sineval var byte[32]
sineval[1] = 128
sineval[2] = 148
sineval[3] = 167
sineval[4] = 185
sineval[5] = 200 etc.

Also for 50Hz,PR2 will be loaded with 78 for 20MHz oscillator frequency of 16f877,but i dont how to arrive in determination of the value loaded for variable'' timerone''.

When i copied the example and try to compile i got the warning 'unable to open include file DT_INTS-18.bas'..what should i do about this?

Finally,is there any other modification i should do in that program that it could work better in pic16f877?

[pxidr84]

You have to download Darrel Taylor's interrupts system : http://darreltaylor.com/DT_INTS-14/intro.html

And put the "DT_INTS-14.bas", etc. into the folder of your source files.

[bwaxing]

Hi,
i have download DT_INTS-14.bas" and DT_INTS-18.bas files and put them in the folder of my source files,when i try to compile the program again the same warning appeared again "unable to open INCLUDE file DT_INTS-18.bas"!

[ScaleRobotics]

Hi,
i have download DT_INTS-14.bas" and DT_INTS-18.bas files and put them in the folder of my source files,when i try to compile the program again the same warning appeared again "unable to open INCLUDE file DT_INTS-18.bas"!

You would need to change the include statement, so that it is using DT_INTS-14 instead of DTS_INTS-18. 18 is for PIC18's, DT_INTS-14 is for lower chips, like PIC17,PIC16 and PIC12's.

Then there are probably different registers that will give you errors, etc. You should be able to change it, (and also the configs), but it will be a little work.

[bwaxing]

hi everybody,

i'm here again with the sinusoidal PWM, please bear with me,

It seems there were some problems with my compiler but after re-installing it,things work pretty well,i've included the file DT_INTS-14.bas in the folder containing the source code and although there some errors,its a good start to me.
there are few things which are not clear to me from the example ofhttp://www.picbasic.co.uk/forum/cont...-DT-interrupts
How to obtain the correspond value for each step is not clear to me,i want to learn how to create a lookup table the way it is done in the example as i dont know how to create it using excel.what formula was used to get these values from that example?
; Set sine "table" in an array
sineval var byte[32]
sineval[1] = 128
sineval[2] = 148
sineval[3] = 167
sineval[4] = 185
sineval[5] = 200 etc.

Also for 50Hz,PR2 will be loaded with 78 for 20MHz oscillator frequency of 16f877,but i dont how to arrive in determination of the value loaded for variable'' timerone''.

Should i include DT_INTS-18.bas file or DT_INTS-14.bas file?it seems to me they perform different functions!which link will i get DT_INTS-18.bas file?

Finally,is there any other modification i should do in that program that it could work better in pic16f877?

Thank you in advance.

[ScaleRobotics]

I don't think your chip has a PLL. So its always best to go with the default configs when you try to change chips. So if you just erase this from the code:

asm
    __CONFIG    _CONFIG1H, _OSC_HSPLL_1H
    __CONFIG    _CONFIG2H, _WDTEN_OFF_2H & _WDPS_512_2H
    __CONFIG    _CONFIG4L, _LVP_OFF_4L
endasm

It will use the defaults located in PBP under your chipname.inc

Then you will get less errors

[bwaxing]

I don't think your chip has a PLL. So its always best to go with the default configs when you try to change chips. So if you just erase this from the code:

asm
    __CONFIG    _CONFIG1H, _OSC_HSPLL_1H
    __CONFIG    _CONFIG2H, _WDTEN_OFF_2H & _WDPS_512_2H
    __CONFIG    _CONFIG4L, _LVP_OFF_4L
endasm

It will use the defaults located in PBP under your chipname.inc


Then you will get less errors

I've removed that part of the code together with other modifications but these two errors kip on coming,i dont how to make it work....

m getting these two assembler errors.
ERROR"INT_Handler"-Interrupt flag(PIR1,TMR1IF) not found.)
ERROR"INT_ENABLE"-Interrupt flag(PIR1,TMR1IF) not found.)

code.

; i'm using pic16f877
;
define OSC 20
;wsave   VAR BYTE    $20     SYSTEM      ' location for W if in bank0
wsave   VAR BYTE    $70     SYSTEM      ' alternate save location for W 
wsave1  VAR BYTE    $A0     SYSTEM      ' location for W if in bank1
wsave2  VAR BYTE    $120    SYSTEM      ' location for W if in bank2
wsave3  VAR BYTE    $1A0    SYSTEM      ' location for W if in bank3
 
ADCON0 = %00000000
ADCON1 = %00000000  ;all anolog output
trisb = %11111111   ;define porta as input
trisc = %11111011   ;make ccp1/portc.2 an output pin
trisa = %11111111   ;define porta as input
TMR2 = 16
PR2 = 34           ;set for 36Khz HPWM(=72 steps*10 times*50hz)        
CCP1CON = %000001100       ;set to pwm mode
T2CON=%00000110           ;enable timer2 and set timer2 prescaler value of 1:4

STEPCOUNT var byte
stepcount = 256

; Set sine "table" in an array
sineval var byte[72]
sineval[1] = 128      ;0 degree
sineval[2] = 137      ;5 degree
sineval[3] = 146
sineval[4] = 154
sineval[5] = 163
sineval[6] = 171
sineval[7] = 179
sineval[8] = 187
sineval[9] = 194
sineval[10] = 200
sineval[11] = 206
sineval[12] = 212
sineval[13] = 216
sineval[14] = 220
sineval[15] = 224
sineval[16] = 227
sineval[17] = 228
sineval[18] = 229
sineval[19] = 230     ;90 degree
sineval[20] = 229
sineval[21] = 228
sineval[22] = 227
sineval[23] = 224
sineval[24] = 220
sineval[25] = 216
sineval[26] = 212
sineval[27] = 206
sineval[28] = 200
sineval[29] = 194
sineval[30] = 187
sineval[31] = 179
sineval[32] = 171
sineval[33] = 163
sineval[34] = 154
sineval[35] = 146
sineval[36] = 137
sineval[37] = 128  ;180 degree
sineval[38] = 119
sineval[39] = 110
sineval[40] = 102
sineval[41] = 93
sineval[42] = 85
sineval[43] = 77
sineval[44] = 69
sineval[45] = 62
sineval[46] = 56
sineval[47] = 50
sineval[48] = 44
sineval[49] = 40
sineval[50] = 36
sineval[51] = 32
sineval[52] = 29
sineval[53] = 28
sineval[54] = 26
sineval[55] = 26
sineval[56] = 26
sineval[57] = 28
sineval[58] = 29
sineval[59] = 32
sineval[60] = 36
sineval[61] = 40
sineval[62] = 44
sineval[63] = 50
sineval[64] = 56
sineval[65] = 62
sineval[66] = 69
sineval[67] = 77
sineval[68] = 85
sineval[69] = 93
sineval[70] = 102
sineval[71] = 110
sineval[72] =119
 
timerone var word 
 
INCLUDE "DT_INTS-14.bas"     ; Base Interrupt System
 
ASM
 
INT_LIST  macro    ; IntSource,        Label,  Type, ResetFlag?
        INT_Handler   TMR1_INT,   _sine,   ASM,  yes
    endm
    INT_CREATE               ; Creates the interrupt processor
ENDASM

T1CON = $31              
TMR1L = 255    ; Prescaler = 8, TMR1ON
TMR1H = 254
@   INT_ENABLE  TMR1_INT     ; Enable Timer 1 Interrupts  
timerone = $FD00                ;gives about 50 hz sine 
Main:
        pause 5
        if timerone = $F9FF then timerone = $FF00
 
GOTO Main
 
'---[TMR1_INT - interrupt handler]------------------------------------------
 
sine:
    TMR1L = timerone.byte0
    TMR1H = timerone.byte1     
    CCPR1L = sineval[STEPCOUNT]>>1 
    stepcount = stepcount -1
    if stepcount = 0 then stepcount = 72
@    INT_RETURN

[ScaleRobotics]

Something is not right. Are you compiling for the right chip, the PIC16F877? Because it does have those registers and bits. Are you using MPASM as your assembler, because the include file requires this. Can you send me your myprogram.lst file? That might tell me more....

[bwaxing]

Something is not right. Are you compiling for the right chip, the PIC16F877? Because it does have those registers and bits. Are you using MPASM as your assembler, because the include file requires this. Can you send me your myprogram.lst file? That might tell me more....

Yes i'm compiling for the PIC16F877 using MPSAM as my assembler

[bwaxing]

I've converted the .lst file into pdf format so that i will be able to attach it,hope it will still serve the purpose.....

[ScaleRobotics]

In fact, your code compiles well over here.

[bwaxing]

Hi, I've been trying to send you the .LST file,but it's bigger than 500000 characters,so i could not upload it on the forum,how should i send it?

[ScaleRobotics]

Hmmm. The thing that jumps out at me a bit is that you are using Mpasm v2.30. I think that came out in 1999. Really! I think it is time to upgrade. See if that helps you. You can get the latest one by downloading MPLAB IDE here: http://www.microchip.com/stellent/id...&part=SW007002

[bwaxing]

Thanks for the tip....yup,it's it working well now....
i'm reading the pic16f877 data sheet page 63 about how to change the duty cycle of th pwm,it says the duty cycle is specified by writing to CCPR1L:CCPCON<5:4>. So in our case does this code below specify the duty cycle?if not where the duty cycle of pwm has been specified in the program?i want to know so that i may modify the duty cycle to make it equal to 90%.
code:

sine:
    TMR1L = timerone.byte0
    TMR1H = timerone.byte1     
    CCPR1L = sineval[STEPCOUNT]>>1 
    stepcount = stepcount -1
    if stepcount = 0 then stepcount = 72

[ScaleRobotics]

Great!

Yes, that is the duty cycle. Why not modify your array for the 90% instead of doing math here? We want to keep multiplication out of our assembly interrupt handler, otherwise, we will need to change it to a PBP type interrupt. And that would take a lot of time for each interrupt, as it needs to save and restore 70 registers each time it interrupts. If you need it to change dynamically, the beauty of an array rather than a lookup, is that you can change it on the fly (doing math in your main).

[bwaxing]

Thanks, i think i got it...let me experiment with the code i have and see what i got.....
thank again..

[bwaxing]

hellow everyone,

I'm simulating this code on proteus Isis but m not getting the expected waveform(sinusoidal wave form)....the code compiles successful...but the waveform i'm getting getting on the scope is not the one...i need help please..

;
define OSC 20

;*****************VARIABLE DECLARATION******************************************
wsave   VAR BYTE    $70     SYSTEM      ' alternate save location for W 
wsave1  VAR BYTE    $A0     SYSTEM      ' location for W if in bank1
wsave2  VAR BYTE    $120    SYSTEM      ' location for W if in bank2
wsave3  VAR BYTE    $1A0    SYSTEM      ' location for W if in bank3
STEPCOUNT var byte                      'Define stepcount as byte type variable
stepcount = 256

;**************SETTING THE REGISTERS WITH APPROPIATE BIT DEFINITION************* 
ADCON0 = %00000000
ADCON1 = %00000000  ;all anolog output
trisb = %11111111   ;define porta as input
trisc = %11111011   ;make ccp1/portc.2 an output pin
trisa = %11111111   ;define porta as input
TMR2 = 16
PR2 = 34           ;set for 36Khz HPWM(=72 steps*10 times*50hz)        
CCP1CON = %000001100       ;set to pwm mode
T2CON=%00000110           ;enable timer2 and set timer2 prescaler value of 1:4

;****************A sine lookup table in an array********************************
sineval var byte[72]
sineval[1] = 128      ;0 degree
sineval[2] = 137      ;5 degree
sineval[3] = 146
sineval[4] = 154
sineval[5] = 163
sineval[6] = 171
sineval[7] = 179
sineval[8] = 187
sineval[9] = 194
sineval[10] = 200
sineval[11] = 206
sineval[12] = 212
sineval[13] = 216
sineval[14] = 220
sineval[15] = 224
sineval[16] = 227
sineval[17] = 228
sineval[18] = 229
sineval[19] = 230     ;90 degree
sineval[20] = 229
sineval[21] = 228
sineval[22] = 227
sineval[23] = 224
sineval[24] = 220
sineval[25] = 216
sineval[26] = 212
sineval[27] = 206
sineval[28] = 200
sineval[29] = 194
sineval[30] = 187
sineval[31] = 179
sineval[32] = 171
sineval[33] = 163
sineval[34] = 154
sineval[35] = 146
sineval[36] = 137
sineval[37] = 128  ;180 degree
sineval[38] = 119
sineval[39] = 110
sineval[40] = 102
sineval[41] = 93
sineval[42] = 85
sineval[43] = 77
sineval[44] = 69
sineval[45] = 62
sineval[46] = 56
sineval[47] = 50
sineval[48] = 44
sineval[49] = 40
sineval[50] = 36
sineval[51] = 32
sineval[52] = 29
sineval[53] = 28
sineval[54] = 26
sineval[55] = 26
sineval[56] = 26
sineval[57] = 28
sineval[58] = 29
sineval[59] = 32
sineval[60] = 36
sineval[61] = 40
sineval[62] = 44
sineval[63] = 50
sineval[64] = 56
sineval[65] = 62
sineval[66] = 69
sineval[67] = 77
sineval[68] = 85
sineval[69] = 93
sineval[70] = 102
sineval[71] = 110
sineval[72] =119
 
timerone var word 
 
INCLUDE "DT_INTS-14.bas"     ; Base Interrupt System

;********Define INT_Handler as ISR********************************************** 
ASM
 
INT_LIST  macro    ; IntSource,        Label,  Type, ResetFlag?
        INT_Handler   TMR1_INT,   _sine,   ASM,  yes
    endm
    INT_CREATE               ; Creates the interrupt processor
ENDASM

T1CON = $31    ; Prescaler = 8, TMR1ON          
TMR1L = 255    
TMR1H = 254
@   INT_ENABLE  TMR1_INT     ; Enable Timer 1 Interrupts  
timerone = $EE16           ;gives about 50 hz sine 
Main:
        pause 5
        'if timerone = $F9FF then timerone = $FF00
 
GOTO Main
 
'---[TMR1_INT - interrupt handler]------------------------------------------
 
sine:
    TMR1L = timerone.byte0
    TMR1H = timerone.byte1     
    CCPR1L = sineval[STEPCOUNT]>>1 
    stepcount = stepcount -1
    if stepcount = 0 then stepcount = 72
@    INT_RETURN

simulation results attached

[ScaleRobotics]

I don't see any kind of wave form on the scope???

[bwaxing]

sure,it is just a line and not a sine wave form as expected....the simulation log say there are attempts to read unimplemented memory locations being ignored..i dont know what does that mean and if it may be one of the cause...i need help.

[sangaboy]

Hi ! demon
I want to generator 3 Phase spwm signal for my final year project but I, m started by understanding single phase SPWM by reading the example from
Microchip appliction notes for sine wave with the 16F series chip..http://ww1.microchip.com/downloads/e...tes/00655a.pdf together with the examples given in http://www.picbasic.co.uk/forum/cont...wave-using-DT- interrupts and http://www.picbasic.co.uk/forum/showthread.php?t=14359.

there are number of things which i've not understand from these readings and i'm asking for help from anyone who can help me to understand.these things are:
1)which formular used to generate a lookup table for the sine waveforms
3)what is the purpose of this piece of code and how to get this values from example of http://www.picbasic.co.uk/forum/cont...-DT-interru and
TMR2 = 117
PR2 = 63

TMR1L = 255
TMR1H = 254

[sangaboy]

Hi to every one
I have worked and modify the code posted by ScaleRobotics and I manage to compile it for the PIC 16F877 and get 2 phase although my output was not very good. my aim is to generate 5kHZ SPWM so that when filtered will give sine waves(50hz). I havebeen reading different application manual and PIC16877 datashet for almost two days but I 'm still in darkness the problem comes for that frequency my duty cycle will have 10bit resolution. here are the questions.

(1) I Try to write the code to FOR 10 bit resolution to PWM module I dont think if is correct.

TeMP = sineval[STEPCOUNT]
    CCP1CON.4 = Temp.0 ' bit 0
    CCP1CON.5 = Temp.1 ' bit 1       
    CCPR1L = Temp.Byte0 >>2  '

(2)when I do my calculation
from microchip application note pwm_frequency=50hz*step*10
which gives me very low step about 10step which is very low when I try to use it my output become very distorted and only CCP1 gives output while ccp2 dont gives any output.

any one can help me how to get 5KHZ 36 step and is it nessary to modify my lookup table for 10bit resolution thankx