Infrared HPWM setup

[astanapane]

Dear all,

just a quick question. I didnt want to open a new thread but most of the Infrared threads are closed.

I would like to set up the PIC18F26k22 in order to use HPWM for the 38khz IR.

First of all i would like to ask if i can use 64Mhz as the main PIC frequency.

i tried to use mister e's pic multi-calc and set 64Mhz. The following are the results i got.



but from the calculations i made:

(64Mhz / (4*TMR2 prescale value * 38Khz))-1 = PR2
(64Mhz / (4*1*38Khz)) - 1 = PR2
(64Mhz / (152000)) - 1 = PR2 <=>

            64,000,000
<=> PR2 =  ------------ -1 <=>
             152,000

<=> PR2 = 420

Also calculating the bits:

              log(FOSC / FPWM)
 Resolution = ------------------- bits
                  Log(2)

log(64,000,000 / 38,000) = 3.226

log(2) = 0.301

so we have:
3.226
------- = 10.17 ~ 10 bits
0.301

and calculating the CCPRL1:

(PR2 + 1) * TMR2 prescale * 50% Duty Cycle = value for CCPRL1, or
(420 + 1) * 1 * 0.50 = 421 * 0.50 = 210

So i set in the code the following:

TRISC.2 = 0 ' CCP1 (PortC.2 = Output)
PR2 = 420 ' Set PWM Period for approximately 38KHz
CCPR1L = 210 ' Set PWM Duty-Cycle to 50%
T2CON = %00000100 ' Timer2 ON + 1:1 prescale --> i know this might not be right as at 64Mhz there is no 1:1 scale based on mister's e multi-calc.
CCP1CON = %00001100 ' Mode select = PWM

could you please help me to clear things up?

I dont mind using 16Mhz as a base frequency, but still the calculations i get are not match with mister's e multi-calc.

Thanks for your help in advance.

[richard]

prescaler is 4 , 16 is also a possibility
(64Mhz / (4*TMR2 prescale value * 38Khz))-1 = PR2
(64Mhz / (4*4*38Khz)) - 1 = PR2
(64Mhz / (152000*4)) - 1 = PR2 <=>


Code:
64,000,000
<=> PR2 = ------------ -1 <=>
152,000*4
<=> PR2 = 104

(PR2 + 1) * TMR2 prescale * 50% Duty Cycle = value for CCPRL1, or
(104+ 1) * 4 * 0.50 = 421 * 0.50 = 210

T2CON = %00000101

PR2 = 104 ' Set PWM Period for approximately 38KHz
CCPR1L = 210>>2 ' Set PWM Duty-Cycle to 50%

note
PR2 is a 8bit reg it cannot ever be 420 or anything larger than 255
CCPR1L are the upper 8 bits of the duty cycle word value
CCP1CON bit 4 and 5 are the lower two bits

[astanapane]

Hi Richard,

thanks for the clarification and answer.

I found in the manual what you said regarding the Resolution bits.

[richard]

the duty cycle is a 10 bit value at best for that chip, not all frequencies can have the full 10bit range available
it totally depends on choices made with regard to prescaler and period.
no matter what bit resolution is possible the CPRxL value is the upper 8 bits of the duty cycle word valueCCP1CON bit 4 and 5 are the lower two bits

[astanapane]

i've also noticed you've shifted 2 bits on the right the CCPR1L

CCPR1L = 210>>2 ' Set PWM Duty-Cycle to 50%

So the CCPR1L value will be 52.

(11010010) 210>>2 = 00110100 = 52

why have we shifted?

[richard]

why have we shifted?
CPRxL value is the upper 8 bits of the duty cycle word valueCCP1CON bit 4 and 5 are the lower two bits



(011010010) 210>>2 = 00110100 = 52 ;high 8bits
(011010010) 210 & 3 = 00000010 = 2 ;low 2 bits

00000010<<4 = 00100000
CCP1CON = 00100000 |12 to set low bits in pwmmode

C version from microchip

void PWM1_LoadDutyValue(uint16_t dutyValue)
{
   // Writing to 8 MSBs of pwm duty cycle in CCPRL register
    CCPR1L = ((dutyValue & 0x03FC)>>2);
    
   // Writing to 2 LSBs of pwm duty cycle in CCPCON register
    CCP1CON = ((uint8_t)(CCP1CON & 0xCF) | ((dutyValue & 0x0003)<<4));
}

[astanapane]

thanks Richard. now is clear.

i will get back once i have a working code and establish an IR communication.

[astanapane]

with the following configuration i got this on the scope. So i guess we are in a good path.

To mention that the main OSC is at 64Mhz using HPWM on the PIC18f26K22 on portc.2

TRISC.2 = 0          ' CCP1 (PortC.2 = Output)
PR2 = 104            ' Set PWM Period for approximately 38KHz
CCPR1L = 52          ' Set PWM Duty-Cycle to 50% (011010010) 210>>2 = 00110100 = 52
T2CON = %00000101    ' Timer2 ON + 4 prescale
CCP1CON = %00001100  ' Mode select %00001100 = PWM

all thanks to Richard.

now im going on the next step.

[richard]

very good.
you could set the lower two bits of the Duty-Cycle word [CCP1CON bits 4:5] to get the duty cycle
even closer to exactly 50%, if you wanted to
CCP1CON = %00101100

[astanapane]

I will do that thanks a lot.

Yesterday i tried till late at night to set a code for the TX and RX, a very simple one but didnt work.

tx:

'*-----------------------------------------------------------------------------|
'*                        |  --------------------- |                           |
'*----------------------- | EUART 1 Configuration  | --------------------------|
'*                        |  --------------------- |                           |
'*-----------------------------------------------------------------------------|                                                                             |
        DEFINE HSER_RCSTA 90h ' Enable serial port & continuous receive
        DEFINE HSER_TXSTA 24h ' Enable transmit, BRGH = 1
        DEFINE HSER_CLROERR 1 ' Clear overflow automatically
        DEFINE HSER_SPBRG 130 ' 9600 Baud @ 64MHz, -0.02%
        SPBRGH = 6
        BAUDCON.3 = 1         ' Enable 16 bit baudrate generator             
'------------------------------------------------------------------------------|

ID	    VAR BYTE
button1 var porta.0  ' we configure this button 1 at porta.0
button2 var porta.1  ' we configure this button 2 at porta.1
RED     var latc.3   ' a RED LED indicates the PIC working condition
Blue    var lata.2   ' a Blue LED indicates the push button everytime

high red
pause 100
low red 
pause 50
high red
'------------------------------------------------------------------------------|
BEGIN:

   ID	= 10
if button1 = 0 then 
    gosub button1_pressed
	endif

low blue
	GOTO BEGIN
'------------------------------------------------------------------------------|

button1_pressed:
high blue
	    hSEROUT [ID]  ' we send at portc.6 which is connected the IR module at the 74LS00 in pin No2 
	    PAUSE 100
    return

button2_pressed:
high blue
	    hSEROUT [ID]  ' we send at portc.6 which is connected the IR module at the 74LS00 in pin No3 
	    PAUSE 100
    return
end

RX:

'*-----------------------------------------------------------------------------|
'*                        |  --------------------- |                           |
'*----------------------- | EUART 2 Configuration  | --------------------------|
'*                        |  --------------------- |                           |
'*-----------------------------------------------------------------------------|                                                                             |

        DEFINE HSER2_RCSTA 90h ' Enable serial port & continuous receive
        DEFINE HSER2_TXSTA 24h ' Enable transmit, BRGH = 1
        DEFINE HSER2_CLROERR 1 ' Clear overflow automatically
        DEFINE HSER2_SPBRG 130 ' 9600 Baud @ 64MHz, -0.02%
        SPBRGH2 = 6
        BAUDCON2.3 = 1         ' Enable 16 bit baudrate generator
        
'-------------------------------------------------------------------------------|
ID	    con 10
Green   var lata.1   ' a Green LED which indicates the 1st output of the IR input code
Blue    var lata.0   ' a Blue LED indicates the 2nd output of the IR input code 
Red     var lata.2   ' a Red LED indicates the PIC working condition
'------------------------------------------------------------------------------|
'                 RED LED indicates that PIC is up and running                 |
'------------------------------------------------------------------------------|

high red
pause 100
low red 
'------------------------------------------------------------------------------|

Begin:

hSERin2 [wait(ID)]
high red
'pause 100

   gosub FIRST_SIGNAL
'   endif

'------------------------------------------------------------------------------|

FIRST_SIGNAL:
high green
pause 500
low green
return

end

[richard]

any Alias that refers to a LATx reg cannot be safely used with HIGH,LOW,TOGGLE or any other pbp high level command
the sort of bugs it can introduce vary from chip to chip and can be difficult to understand , don't do it

Blue var lata.2 '; an alias to a lata

high blue ; will not work safely
blue = 1 ; will work
low blue ; will not work safely
blue = 0 ; will work
toggle blue ; will not work safely
blue = !blue ; will work
etc...

Yesterday i tried till late at night to set a code for the TX and RX, a very simple one but didnt work.

how are the chips connected , show a schematic

[astanapane]

I will make the schematic on paper later today and will upload it here.

thanks

[Ioannis]

any Alias that refers to a LATx reg cannot be safely used with HIGH,LOW,TOGGLE or any other pbp high level command the sort of bugs it can introduce vary from chip to chip and can be difficult to understand , don't do it

Blue var lata.2 '; an alias to a lata

high blue ; will not work safely

Though this is the recommended way to control output pins. I suppose this was before LAT registers showed up?

Ioannis

[astanapane]

Please find the schematic as follows.

I hope i didnt forget anything. In any case is very simple.

[richard]

if you look at the data sheet for a tsop4838 you will see that you have a numbers of issues to contend with


1. @9600baud the bit time is 100uS or approx 4 cycles of 38khz , about 2 to three times faster than the tsop4838 can cope with
2. the max burst rate is 800/sec a 9600baud stream can exceed that
3. after a 70 cycle transmission a 12 cycle min tx gap must be made [some devices can lock up if u don't and need a pwr cycle to recover]
4. the device will do its very best to reject a continuous transmission and go mute till a min tx gap in tx is observed, which is what you are doing.

overall tsop4838 is not particularly suitable for serial tx from a uart, you could try a much lower baud rate and you will need to
invert the transmission logic so that there no transmission at idle

i would also wire tx to rx directly to verify code works before trying ir link, also have a look at Manchester encoding and check out ir tx protocols like RC5/6 NEC etc

[astanapane]

Hi Richard,

you are right, i have decreased the speed and manage to play a lit bit with the delay in useconds.

I worked somehow but not always reliable.

I think i will try the RC5 method.

[richard]

I worked somehow but not always reliable.

the series resistor for the led is wat too big, it will make range / reliability pretty low. it could go as low as 39 ohms safely [probably lower even] in a non continuously on configuration otherwise 100 ohm would be better

[astanapane]

I will try to change that as well before i go for the RC5.

The following 15 days i will be in a business trip in Abu Dhabi so i will get back as soon as i have time to check this out.

Many thanks.

[tumbleweed]

You can get rid of the transistor and associated resistors and just connect the OUT directly to RB7.

If you need to, you can invert the RX sign with the DTRXP bit in the baudcon register.

[mpgmike]

the series resistor for the led is wat too big, it will make range / reliability pretty low. it could go as low as 39 ohms safely [probably lower even] in a non continuously on configuration otherwise 100 ohm would be better

For most LEDs or SSRs, I found 470 ohms offers a good compromise between response time and effectiveness.