Voltage output from PIC16f628A

[mister_e]

your CCP definition are fine for 4MHZ, but not for 10MHZ.

download this tool bellow
http://www.picbasic.co.uk/forum/showthread.php?t=4994

it will give you some answer.

1. This voltage i require is to be read by a vehicle ecu. If you use PWM will it see that as a voltage or will it see the pulses?

More than likely it will see pulses. You have to convert it to pure DC with a simple RC filter... better if you add a op-amp buffer in between.

[bennamanna]

Gday,

Thanks again for your reply. I will use a rc filter as you suggested.

I have downloaded your calc. It looks like it would be verry usefull. As stated I am a beginner ;- ( Could you please step me through what I have to enter in to your calc and my code to fix it? I will learn this way.

Thanks,

Ben

[mister_e]

you just need to enter the OSC speed and expected frequency. it will give you...
<img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=1168&stc=1&d=116295770 1">
There, you have the
prescaller => 1:16 => see T2CON setting in your datasheet
PR2 => 155 => directly

It also give you the value for 100% duty cycle => 625

If you want to set different DutyCycle, move the scroll bar at the top right. The duty value will be reported in the 'results' section at the bottom.

Not much.

[bennamanna]

Gday again,

Thanks for that info. I changed the PR2 as per your calculation. It still does not seem to give the same value as I enter in the terminal application. If I am correct in my coding, if I send it 100 with a terminal app 100 should display on the LCD and it should set the duty cycle to 100. This is not the case. It says 34 on the LCD and reflects that in the duty cycle.

Any ideas?

Thanks,

Ben

[mister_e]

I don't know wich terminal software you're using but be sure it send ASCII character and use the right modifier in your Serin/Serin2/DEBUGIN/HSERIN line.

Look for # or DEC.

Also, make sure your terminal software don't send cr and lf character.

Once you're sure of it, you should have better results.

If you send 100 and receive it correctly, you should have a 16% duty cycle.

[bennamanna]

Gday,

I am using serial communicator that is with microcode studio. I cant see a setting to ensure it is sending ascii. I made sure it was not sending cr and it made no diference.

The code I am using is below.

NCLUDE "modedefs.bas" ' Include serial modes
SI VAR PORTB.1 ' Serial Input pin
B0 VAR BYTE
Define OSC 10

Define LCD_DREG PORTA ' RA0..3
Define LCD_DBIT 0
Define LCD_RSREG PORTA ' RA6
Define LCD_RSBIT 6
Define LCD_EREG PORTA ' RA4
Define LCD_EBIT 4
Define LCD_BITS 4
TRISA = 0
TRISB = 0
CMCON = 7

Pause 1000 ' Wait for LCD to startup

duty VAR BYTE ' Duty cycle value (CCPR3L:CCP3CON<5:4>)

TRISB.3 = 0 ' Set PORTB.5 (CCP3) to output
CCP1CON = %00001100 ' Set CCP3 to PWM
T2CON = %00010101 ' Turn on Timer2, Prescale=4

PR2 = 155 ' Set PR2 to get 1KHz out
duty = 100 ' Set duty cycle to 20%

loop:
SerIn SI,T9600,,duty
if duty > 625 then
LCDOut $FE,1 ' Clear LCD screen
LCDOut "Duty to great" ' Display line 1
goto loop
endif

CCP1CON.4 = duty.0 ' Store duty to registers as
CCP1CON.5 = duty.1 ' a 10-bit word
CCPR1L = duty >> 2

'duty = duty + 5 ' Increase duty cycle
LCDOut $FE,1 ' Clear LCD screen
LCDOut # duty ' Display line 1

GoTo loop ' Do it forever

Any other ideas why it is not receiving the same as I send it?

Thanks,

Ben

[sayzer]

hi Ben,

Since our PICs are serial processors, at least for now, and must execute the instructions serially, that is to say one line or instruction at a time, you will never get Serin and Serout commands working at the same time.

If you use hardware USART, then it will be working in the background, so that you can receive something at the same time you send it.


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