PBP projects for R/C models

[Kenjones1935]

I am realizing that using PAUSE can not work if my PIC is meant to do some thinking between pulses. I just discovered

http://darreltaylor.com/DT_INTS-14/SPWM.html

He is using interrupts. That is what I was hoping to do in the first place. I'll see if I can figure out what he is saying.

Meanwhile, would you be willing to take pictures of the pulses that my code is making if I posted the code?

Ken

[ScaleRobotics]

Sure! Post what you have, and I will send you some oscilloscope shots.

[Kenjones1935]

Scalerobotics:

This snippet has the capabiltiy to increment the pulse size a little bit at a time.

With this code the car starts out driving very fast backwards, then after five to ten seconds it stops, but never starts up forward.

My theory is that the (PAUSE 20) is what is causing the 50 pulses per second, Is that correct?

duty	VAR	WORD		' Duty cycle value (CCPR1L:CCP1CON<5:4>)
range   VAR word
segment   var word 
		TRISC.2 = 0				' Set PORTC.2 (CCP1) to output
		CCP1CON = %00001100		' Set CCP1 to PWM 
		T2CON = %00000101		' Turn on Timer2, Prescale=4

' Use formula to determine PR2 value for a 1KHz signal, 
' 4MHz clock, and prescale=4. (4E6/(4*4*1E3))-1=249
'		PR2 = 249				' Set PR2 to get 1KHz out
'		PR2 = 499				' Set PR2 to get 2KHz out
	
' Use formula to determine CCPR1L:CCP1CON<5:4> value for
' ends of range 20% to 80%.  (249+1)*4*0.2=200 (20% value)
' (249+1)*4*0.8=800 (80% value)
'       duty = 200	' Set duty cycle to 20%

       range = 25
       duty = 1650	' Set duty cycle to 1.65msec      
       segment = 0

mainloop:	CCP1CON.4 = duty.0		' Store duty to registers as
		CCP1CON.5 = duty.1		' a 10-bit word
		CCPR1L = DUTY >> 2
		Pause 20				' Pause 1/50 of second
       duty = duty + 2    ' Increase duty cycle




		IF (duty < (1650 + segment + range)) Then mainloop	' Do it again unless 2 msec

		duty = duty + 2				' Reset to 20% duty cycle

		segment = segment + range
        
        PAUSE 2000      'Pause 2 seconds				
        
       	GoTo mainloop				' Do it forever

[ScaleRobotics]

Here is the result. It changes from off through the percentage points to all the way on, but the period remains constant at about 1.023ms. (I finally got my oscilloscope USB driver to work today!)

[Kenjones1935]

Thank you soooo much. What a great tool..

Two things for me to consider.

1. PAUSE seems to not have the affect I expected.
2. The PR2 constant must mean something to PBP, but I can not figure out what.

Lastly, which version of oscilloscope software do you use? Is it freeware or did it cost money. If so, how much?

Ken

[Kenjones1935]

The following code makes the car go full speed backwards, then stop, then full speed forwards, then stop etc. Using the RC system I can control the motor continuously though varying speed. I have not yet figured what HPWM parameters produce various speeds to the ESC. It may be that the over-specification fast pulse frequency is overriding that nuance.

To really discover what this is doing I need to study and understand the ASM code. I think HPWM is interrupt driven. I am concerned because page 87 of the PBP Manual seems to say that the slowest pulse frequency is 245 hz. I want 50 hz.

'****************************************************************
'*  Name    : HPWMcommand.BAS                                   *
'*  Author  : Ken Jones                                         *
'*  Notice  : Copyright (c) 2010 [select VIEW...EDITOR OPTIONS] *
'*          : All Rights Reserved                               *
'*  Date    : 1/27/2010                                         *
'*  Version : 1.0                                               *
'*  Notes   : PBP has a HPWM command.  Let's try it.                                                  *
'*          :                                                   *
'****************************************************************
' Don't forget. The duty cycle is 0 to 256 resolution
MAINLOOP:
  HPWM 1,110,50     ' Neutral discovered by experiment.
  PAUSE 5000
  HPWM 1,64,50      ' Full backwards
  PAUSE 2000
  HPWM 1,110,50
  PAUSE 5000
  HPWM 1,164,50     ' Full forward
  PAUSE 2000
 goto mainloop

Ken

[rmteo]

....I am concerned because page 87 of the PBP Manual seems to say that the slowest pulse frequency is 245 hz. I want 50 hz.

Period = [(PR2) + 1] * 4 * TOSC *(TMR2 Prescale Value)
Frequency = 1/Period

Therefore with a 4MHz clock, the lowest frequency is 244Hz.