Low cost audio function generator(DDS)

**sougata** · - 12th December 2006, 05:40

Dear Steve,

Thanks for replying. Actually I live in a part of my country where sourcing of specialized components is a real problem. Initially I considered using a DDS chip. But set back due to unavailability. Frequency range is within 10K. I haven't done the homework yet. Just trying to get some guidelines whether to base it on a 16F. The possibility you can say. If it is technically possible then I might consider using a 18F too. That depends on the overall BOM cost.

**Acetronics2** · - 12th December 2006, 09:12

Hi, Sougata

ICL 8038, voltage controlled ??? ... you use the Pic as the freq regulator ... say, you build a simple PLL !!! but 8038 outputs some sinewaves ...

bad idea ???

Alain

**sougata** · - 12th December 2006, 11:11

Dear Alain,

Thanks for your reply. I just don't want to go the conventional (traditional)way. I have used MAX038 (big brother of XR8038) earlier but it was a pure analogue design with some fancy digital control as you mentioned. This project is all about low cost and best control. In fact with a PC side software the lookup tables could be modified to generate other waveforms as well. I am asking you guys for the possibility on a 16F. Storing one quadrant of data in the lookup table and building the sinewave is easy. But while modulating it, for a 8bit modulation index, I am doubtful on the processor througput considering 16/32 bit math. If there is an easy way out to do this in software please guide.

**Acetronics2** · - 12th December 2006, 11:20

Hi, Sougata

Here, you will find such a DDS module ... for the price ... just tears left !!!

http://shop.elv.de/output/controller...0&detail2=6325

or here, with a PC interface:

http://shop.elv.de/output/controller...&detail2=10617

Alain

**Ingvar** · - 12th December 2006, 12:25

Hi Sougata,

I did some experimenting with DDS a few years ago, i wrote this piece of code. If my memory serves me right, it worked up to 20kHz with reasonable good looking sine on the output. I also did some testing with PWMoutput but never got good results with that, there may be some leftovers in the program from that ...... just remove.

Code:

'****************************************************************
'*  Name    : DDS16F.BAS                                        *
'*  Author  : Ingvar Gillholm                                   *
'*  Date    : 2004-03-11                                        *
'*  Version : 1.0                                               *
'*  Notes   : This program produces a sinewave through PortB,   *
'*          : which should have a R-2R leadder connected to it. *
'****************************************************************


@ device  pic16F876, hs_osc, wdt_off

define OSC 20
'DEFINE LOADER_USED 1

TonePort    VAR PortB
CheckNew    VAR PortA.3

Phase       VAR BYTE[3] BANK0
Freq        VAR BYTE[3] BANK0
Zero        VAR BYTE    BANK0

TempVar     VAR BYTE

ADCON1 = 7      'Porta is digital
TrisA = $ff     'All inputs
PortB = 0       'Start with all outputs low
TrisB = 0       'All outputs            
Zero = 0

PR2 = $3f
OUTPUT PortC.2
T2CON = %00000100
CCP1CON = %00001100
GOTO New

Main:
asm
;
;======================== MAIN LOOP =========================
;

    bcf STATUS,RP0
    bcf STATUS,RP1

Loop
    BTFSC   _CheckNew     ; Check for a new	frequency
    GOTO    _New          ; and get new frequency
                          ;
	MOVF	_Freq,W       ; Get the current frequency
	ADDWF	_Phase,F	  ; and increment the phase
	btfss STATUS,C        ;
    goto NoCarry          ;burn time if no carry
	incf _Phase+1         ;
	btfsc STATUS,Z        ;
	incf _Phase+2         ;
AfterCarry	              ;
	MOVF	_Freq+1,W     ;
	ADDWF	_Phase+1,F    ; 
	btfsc STATUS,C        ;
	incf _Phase+2	      ;
	MOVF	_Freq+2,W	  ;
	ADDWF	_Phase+2,F    ;

	MOVF	_Phase+2,W	  ;

	ANDLW	07Fh		  ;Reduce to 7 bits for 180 degrees
	CALL	SineTbl		  ; and get amplitude
    
	BTFSS  _Phase+2,7	;Is amplitude supposed to be negative?
	SUBWF  _Zero,w		;Change polarity of sine amplitude
   	
    MOVWF	_TonePort     ;Output to DAC
	GOTO	Loop		  ;

NoCarry
    goto AfterCarry

;*********** SINE TABLE ****************

SineTbl
	ADDWF  PCL
    retlw 080h
    retlw 083h
    retlw 086h
    retlw 089h
    retlw 08Ch
    retlw 090h
    retlw 093h
    retlw 096h
    retlw 099h
    retlw 09Ch
    retlw 09Fh
    retlw 0A2h
    retlw 0A5h
    retlw 0A8h
    retlw 0ABh
    retlw 0AEh
    retlw 0B1h
    retlw 0B3h
    retlw 0B6h
    retlw 0B9h
    retlw 0BCh
    retlw 0BFh
    retlw 0C1h
    retlw 0C4h
    retlw 0C7h
    retlw 0C9h
    retlw 0CCh
    retlw 0CEh
    retlw 0D1h
    retlw 0D3h
    retlw 0D5h
    retlw 0D8h
    retlw 0DAh
    retlw 0DCh
    retlw 0DEh
    retlw 0E0h
    retlw 0E2h
    retlw 0E4h
    retlw 0E6h
    retlw 0E8h
    retlw 0EAh
    retlw 0EBh
    retlw 0EDh
    retlw 0EFh
    retlw 0F0h
    retlw 0F1h
    retlw 0F3h
    retlw 0F4h
    retlw 0F5h
    retlw 0F6h
    retlw 0F8h
    retlw 0F9h
    retlw 0FAh
    retlw 0FAh
    retlw 0FBh
    retlw 0FCh
    retlw 0FDh
    retlw 0FDh
    retlw 0FEh
    retlw 0FEh
    retlw 0FEh
    retlw 0FFh
    retlw 0FFh
    retlw 0FFh
    retlw 0FFh
    retlw 0FFh
    retlw 0FFh
    retlw 0FFh
    retlw 0FEh
    retlw 0FEh
    retlw 0FEh
    retlw 0FDh
    retlw 0FDh
    retlw 0FCh
    retlw 0FBh
    retlw 0FAh
    retlw 0FAh
    retlw 0F9h
    retlw 0F8h
    retlw 0F6h
    retlw 0F5h
    retlw 0F4h
    retlw 0F3h
    retlw 0F1h
    retlw 0F0h
    retlw 0EFh
    retlw 0EDh
    retlw 0EBh
    retlw 0EAh
    retlw 0E8h
    retlw 0E6h
    retlw 0E4h
    retlw 0E2h
    retlw 0E0h
    retlw 0DEh
    retlw 0DCh
    retlw 0DAh
    retlw 0D8h
    retlw 0D5h
    retlw 0D3h
    retlw 0D1h
    retlw 0CEh
    retlw 0CCh
    retlw 0C9h
    retlw 0C7h
    retlw 0C4h
    retlw 0C1h
    retlw 0BFh
    retlw 0BCh
    retlw 0B9h
    retlw 0B6h
    retlw 0B3h
    retlw 0B1h
    retlw 0AEh
    retlw 0ABh
    retlw 0A8h
    retlw 0A5h
    retlw 0A2h
    retlw 09Fh
    retlw 09Ch
    retlw 099h
    retlw 096h
    retlw 093h
    retlw 090h
    retlw 08Ch
    retlw 089h
    retlw 086h
    retlw 083h

ENDASM
New:
' The frequency is calculated as FreqValue = DesiredFreq/((1/2^24)*(5*10^6/28))
' Same as FreqValue = DesiredFreq/((1/16777216)*(5000000/28))
' Same as FreqValue = DesiredFreq*16777216*28/5000000
' Same as FreqValue = DesiredFreq*93,9524096
' The resolution is 1/93,9524096 = 0,01064368656703404........Hz

' The eight frequencies selected for this test is........
'  67,0 = 001896
'  94,8 = 0022CA
' 118,8	= 002B99
' 146,2	= 0035A7
' 173,8	= 003FC8
' 199,5	= 004937
' 225,7	= 0052D5
' 254,1 = 005D41

    TempVar = PortA & %00000111     'Only lower 3 bits
'    LOOKUP TempVar,[$00,$00,$00,$00,$00,$00,$00,$00],Freq[2]    'Stuff Hibyte            
'    LOOKUP TempVar,[$1a,$25,$2e,$39,$44,$4e,$58,$63],Freq[1]    'Stuff Midbyte
'    LOOKUP TempVar,[$58,$47,$b7,$7d,$57,$72,$c0,$eb],Freq[0]    'Stuff Lowbyte
    LOOKUP TempVar,[$00,$00,$00,$00,$00,$00,$00,$00],Freq[2]    'Stuff Hibyte            
    LOOKUP TempVar,[$18,$22,$2b,$35,$3f,$49,$52,$5d],Freq[1]    'Stuff Midbyte
    LOOKUP TempVar,[$96,$ca,$99,$a7,$c8,$37,$d5,$41],Freq[0]    'Stuff Lowbyte    
    GOTO Main
END

Doing amplitde control is probably too much to ask from a 16F@20MHz but a 18F@40MHz might be able to pull it off.

/Ingvar

**sougata** · - 12th December 2006, 12:39

Hi All,

Thanks Ingvar at least you share the same vision as me.

Doing amplitde control is probably too much to ask from a 16F@20MHz but a 18F@40MHz might be able to pull it off.

Actually my client wants to put this module into a breadboard trainer to make it compete better. he does'nt want to increase the manufacturing cost however.

Because the amplitude control will also be used to modulte the base sinewave at a lower frequency it needs to be computed on the fly through a modulation index (I suppose).

Thanks Alain for the link but I cannot read German.(I am not sure even if it is German at all)

**Acetronics2** · - 12th December 2006, 12:46

Originally Posted by sougata

Hi All,

Thanks Alain for the link but I cannot read German.(I am not sure even if it is German at all)

The only interesting info here is the price reached ... ~ 50 US $ ( sold ...) .

Alain

speck · - 12th December 2006, 23:15

Hi Ingvar-

Could this be made to work using the HPWM output & a timer interrupt to output very low frequency sine waves? (< 30hz) Using a lookup table & a variable timer interrupt cycle to vary the sample rate/freq. of the sine? Perhaps amplitude could be varied by scaling the wavetable values?

Was it the case that the PWM output didn't give you a smooth sine at higher frequencies? Or it just didn't work well at all?

Originally Posted by Ingvar

I did some experimenting with DDS a few years ago, i wrote this piece of code. If my memory serves me right, it worked up to 20kHz with reasonable good looking sine on the output. I also did some testing with PWMoutput but never got good results with that, there may be some leftovers in the program from that ...... just remove.
Doing amplitde control is probably too much to ask from a 16F@20MHz but a 18F@40MHz might be able to pull it off.

/Ingvar

**Archangel** · - 13th December 2006, 00:34

10-MHz-DDS-Funktionsgenerator mit PC-Softwaresteuerung-preis:69,95 euro
Das ist gut, Ya ?

Thread: Low cost audio function generator(DDS)

Thread Tools

Search Thread

Display

Hybrid View

Unavailability of components

Down memory lane

Commercial example ...

Thanks Ingvar

comment

Similar Threads

Old and beyond help ?

Pic16f84 and RC5 kode

Microcontroller with 2 way paging application problem

Problems with RC2 and RC3

4-line LCD Help - using PortA instead of B

Members who have read this thread : 0

Bookmarks

Bookmarks

Posting Permissions