I want to control the volume of the output using Sound command.

[billys7]

My issue is that i don't know how to create white noise, without using the SOUND command.
If i knew, it would be easier to me, to make the pattern of the sound i want.

The other choice is to to connect the output of the sound to a transistor and with an interrupt and PWM output to the base of the transistor.

[AvionicsMaster1]

To me, white noise is a random frequency in the audible range. Using the SOUND command gives you a specific frequency. Packing together commands to give you a randomish frequency won't be what I think of as white noise.

To make a specific sound, as the whistle on a train, or music, the chuff-chuff sound, will require you to know the frequency or key of the sound and use the sound command to approximate it.

From experience I've found feeding the output from a 12F683 into a speaker doesn't generate a very "loud" sound. You'll have to amplify it somehow and I don't know why you couldn't use a pin off the the chip to control the volume of the sound. I'm sure someone will shoot a hole in that theory but why not?

I'm thinking if you're going to go through that trouble why don't you get an actual recording of the train whistle or horn signals and put them on a SD card and just have it play into the amplifier? Might be easier and sound better than trying to approximate locomotive horn signals with a PIC.

My nickels worth.

[billys7]

Actually, If i knew the frequency of sound command 255, which is a white noise, it would be easy for me to edit it.
Paco here http://usuaris.tinet.cat/fmco/dccfunc_en.html has made it with Tushuuu and assembly.

He uses TMR2 as PWM generator for sound, Vref module for volume control, TMR1 for Envelope timing, TMR0 for software noise generator, internal comparator for mixing sound and noise.
RB0 is DCC input, RB3 (PWM) conected to RA1 (comparator), RA2 outputs to a buffer OPAMP, RA4 to OPAMP output throught a resistor and to another OPAMP buffer for output to a buzzer.

The size of the circuit is the reason that i need software edit of the sound. The circuit must be very small.

[billys7]

I wrote this, but it is very slow.
The pic is 16F1824, and RA2 is connected to the base of BC547, RC3 to opamp and the output of the opamp to the collector of BC547 and emmiter to speaker.


@ __config _CONFIG1, _FOSC_INTOSC & _WDTE_OFF & _PWRTE_ON & _MCLRE_OFF & _CP_OFF & _CPD_OFF & _BOREN_OFF & _CLKOUTEN_OFF & _IESO_OFF & _FCMEN_OFF
@ __config _CONFIG2, _WRT_OFF & _PLLEN_OFF & _STVREN_OFF & _BORV_19 & _LVP_OFF

DEFINE OSC 4

OSCCON = %01101000 '4mhz oscillator

DEFINE CCP3_REG PORTA 'Channel-1 port
DEFINE CCP3_BIT 2 'Channel-1 bit

TRISA = 0
TRISC = 0 ' OUTPUT
ANSELA = 0
ANSELC = 0

OPTION_REG.7=0 ' Weak pullup enabled
OPTION_REG.6=0 ' Interrupt Edg Select bit
OPTION_REG.5=0 ' TMR0CS Timer0 Clock Source select
OPTION_REG.4=0 ' TMR0CS Timer0 Source edge select
OPTION_REG.3=0 ' Prescaller assignemnet (0-> timer0)
OPTION_REG.2=1 ' Prescaller rate
OPTION_REG.1=1 ' Prescaller rate
OPTION_REG.0=1 ' Prescaller rate
'Prescaler 1:256, INTERRUPT every 65,536ms


x var BYTE

ON INTERRUPT GOTO ISR
INTCON = %10100000 ' enable TMR0 and GLOBAL
X = 0

GOTO START

START
sound portc.3, [255, 65535]
goto START


ISR:
disable
X=X+5
IF X>255 THEN
X=0
ENDIF

hpwm 3,x,20000

INTCON.2=0

resume
enable

end

Where is my mistake ?

[HenrikOlsson]

Hi,
First of all, the manual states that the duration part of the sound statement should be 0-255, you're specifying 65535.
Second, and what I think is the main "mistake", is in your interpretation of how ON INTERRUPT works.

ON INTERRUPT isn't a real hardware interrupt. It will only check the interrupt flag between each PBP statement. If you specify a sound duration of 255 the sound command takes 255*12ms=3060ms so the ISR will only execute once ever ~3 seconds even if TMR0 overflows once every 65ms. Had it worked with 65535 as the duration the ISR would only execute every 786th second.

Finally, doing things like IF X>255 THEN when X is declared as a BYTE doesn't do anything because X can never be larger than 255 anyway. You can safely keep adding 5 to it, it will wrap around by itself.

Hope it helps.

/Henrik.

[billys7]

Yes you are right.
How can i make a real interrupt ?

[mackrackit]

You can use
http://darreltaylor.com/DT_INTS-14/intro.html
This is the easy way.

Or you can read in the manual for an explanation on how to write your own.