PBP projects for R/C models

[Kenjones1935]

At last I am getting the correct reference materials.

DS33014K is telling me about MPASM Assembler, Library and Linker.

I have ordered from Belgrade "PIC Microcontrollers". It is being shipped by air. That alone is pretty amazing. Just a little paperback book.

I have also found an online book at:

http://www.mikroe.com/en/books/picmcubook/ch0/

It may be the same book only on line. I am old fashioned. I like to read from paper.

I have plenty of studying to do. Thank you again and again.

Ken

[Kenjones1935]

I copied your code snip from POST #73 at 3:02 on the 28th of January.

I noticed in the .asm code that it wanted to:

INCLUDE "MACKRA~1.MAC"

There is no such file in my computer. Do I need a copy? May I have one?

Also the compiler complained that:

Error 118: "Overwriting previous address contents (2007)

Page 157 of DS33014K says that Error 118 occurred because "Code was previously generated for this address" I assume it is talking about address (2007). I do not see where in the .asm code this is happening. I do not even know what to look for.

Ken

[Kenjones1935]

Mackrackit,

From what I understand your code will do a PWM every time TMR0 overflows.

What I need to do is make this overflow happen every 20ms. That is 50 pulses per second. We have a 4 meg oscillator. If I were designing this counter I think I would have it set to 20,000 each time it overflows. I gather from page 74 of the Data Sheet that this is not possible. The biggest prescaler is 256.

How about a routine that counts these interrupts until 1/50 of a second has elapsed then calls PWM? I would have it send one pulse out pin 1 with the duty as defined by "duty". It would look like

PWM 1,duty,1

I have found a section on Timers in a book called Running Small Motors with PIC Microcontrollers that has an example of MicroEngineering Labs code that makes an eight digit LCD display the time in hours, minutes and seconds. I think this code must do something like I need.

Ken

[rmteo]

You want 20,000 counts before it overflows. Setting the prescaler to 1:256, you will need 20,000/256 counts = 78. The counter rolls over (overflows and sets T0IF) when it reaches 255, so if you pre-load it with 255-78 = 177, then it will overflow approximately every 20mS.

[mackrackit]

I copied your code snip from POST #73 at 3:02 on the 28th of January.
I noticed in the .asm code that it wanted to:
INCLUDE "MACKRA~1.MAC"
There is no such file in my computer. Do I need a copy? May I have one?

Looks like you have the code named MACKRACKIT?
The *.MAC file is the macro file generated by PBP. It will be in your project directory. The name is chopped to the 8.1? standards.

Also the compiler complained that:
Error 118: "Overwriting previous address contents (2007)
Page 157 of DS33014K says that Error 118 occurred because "Code was previously generated for this address" I assume it is talking about address (2007). I do not see where in the .asm code this is happening. I do not even know what to look for.

Ken

Looks like you are setting the configs in the *.inc file. I have them in the code. Just comment that line out and it should be OK.

[mackrackit]

Mackrackit,
From what I understand your code will do a PWM every time TMR0 overflows.

The code in post #73 will toggle a LED when TMRO overflows. The LED on PORTD.7 will gradually become brighter then turn off and start over again.

This was just an example of an interrupt working with something else going on.

You do have to be careful with this as things will sometimes not work as expected. Like they say, the machine will do what it is told, not what you want

This is the same code as in post #73 with some modifications to demonstrate a "pitfall".
The START loop still has PORTD.7 PWMing the LED with PORTD.0 added to be toggled.
Inside of the interrupt loop the same PWM that is on PORTD.7 is now on PORTD.6.

What do you think will happen?
What does happen?

'16F887 INT RUPT
'44 PIN DEMO BOARD

 @ __config _CONFIG1, _INTRC_OSC_NOCLKOUT & _WDT_ON & _MCLRE_OFF & _LVP_OFF & _CP_OFF

 INTCON.5 = 1    'ENABLE TMR0  DATA SHEET SECTION 14.3.2
 OSCCON = %01110000 '8 Mhz
 OPTION_REG = %10000111  ' 1:256 PRESCALE
 ON INTERRUPT GOTO TLOOP
 CNT  VAR BYTE
 D    VAR BYTE
 D = 0
 HIGH PORTD.0
 PAUSE 500

 START:
 FOR CNT = 0 TO 150
 PWM PORTD.7,D,100
 D = D + 2
 NEXT CNT
 TOGGLE PORTD.0
 PAUSE 100
 GOTO START

 DISABLE
 TLOOP:
 INTCON.2=0 ' DATA SHEET SECTION 14.3.2
 TOGGLE PORTD.4
 FOR CNT = 0 TO 150
 PWM PORTD.6,D,100
 D = D + 2
 NEXT CNT
 RESUME
 ENABLE

[Kenjones1935]

Just like you said it would.

Now on to your next one. It compiles and works also. I see what it does. I need to figure out how.

Thank you!!

[Kenjones1935]

Can anyone point me to a definition of "prescaler".
What I thought it meant does not seem to jive with what I am seeing.

Ken

[Kenjones1935]

"Running Small Motors with PIC Microcontrollers" says, on page108

"A pre-scaler is applied to the system clock and affects the timer by slowing down the system clock as it applies to the timer. Normally the timer is fed by a fourth of the basic clock frequency, which is called Fosc/4. In a system running a 4 MHz the timer sees a clock running at 1 MHz. If the pre-scaler is set for 1:8, the clock will be slowed down by another eight times, and the timer will see a clock at 125kHz."

"The post-scaler setting determines how may overflows will go by before an interrupt is triggered."

If I pre-scale TMRO 1:256 I will get overflows at about 4K per second. If I add a post-scaler of 1:64 I will end up with about 62 interrupts per second.

Close enough for government work?

Ken

[Kenjones1935]

I just found in DS33023 section 11.6.

"There is only one pre-scaler available which is mutually exclusively shared between Timer 0 and Watchdog Timer."

So I have to count the 4000 Interrupts per second using a

FOR CNT To 80
NEXT

loop. That will give me much closer to 50 pulses per second.

Correct?

[rmteo]

See my post #84 above. Which part is unclear to you?

[mackrackit]

Hi Ken,

I always get confused with this part of things too, so I will just point you to a couple of threads that I refer to when the need arises.

I think maybe the parts about
TMR1L
TMR1H
are the things you need to look at???

http://www.picbasic.co.uk/forum/showthread.php?t=961
http://list.picbasic.com/forum/messa...tml?1049090059

[Bruce]

You could simplify this a great deal if your PIC has Timer1 available, and Compare,
Capture, PWM .. by just using the Compare peripheral.

Here's an example:

    DEFINE OSC 4

    Match VAR WORD
    
    Match   = 20000         ' 20,000 * 1uS = 20mS until compare match
    CCPR1H  = Match.HighByte' Load compare register high
    CCPR1L  = Match.LowByte ' Load compare register low
    CCP1CON = %00001011     ' Compare mode, auto reset Timer1
    
    '/ TRIS & Port Setup
    PORTB.0=1
    TRISB = $FE  ' PORTB.0 output, rest inputs
    
    '/ disable interrupts
    INTCON.7 = 0 ' Disable global ints
    INTCON.6 = 0 ' Disable peripheral ints
    PIE1.0   = 0 ' Disable Timer1 int
    PIE1.2   = 0 ' Disable CCP1 int

    T1CON = %00000000 ' Timer1 off, internal clock, 1:1 prescale
    TMR1H = 0         ' Clear Timer1 high
    TMR1L = 0         ' Clear Timer1 low
    
    T1CON.0 = 1  ' Turn on Timer1

LOOPS: ' NOTE: PIR1.2 is the CCP1IF compare interrupt flag bit.
       ' this bit is set when Timer1 reaches the value in
       ' CCPR1L & CCPR1H
    IF PIR1.2 = 1 THEN   ' If CCP1 to TMR1 compare match occured
       PORTB = PORTB ^ 1 ' Toggle PORTB.0
       PIR1.2 = 0        ' Clear compare interrupt flag bit
    ENDIF
    GOTO LOOPS

    END

Just 1 single interrupt could take care of your 20mS timing VS a bunch to accumulate the
total 20mS time period.

A single interrupt every 20mS & no reloading anything. Timer1 is automatically cleared on
match, and the CCPR1L/CCPR1H registers contain the value loaded into them until you
change it.

[rmteo]

For 20mS timing, you can do it with a single interrupt with any of the 3 timers on the PIC16F887.

Timer0 - Set prescaler to 1:256
Timer1 - As shown above by Bruce
Timer2 - Set prescaler to 1:16, set postscaler to 1:16

[Kenjones1935]

It seems to me that the most important feature that must be continuously timed in my RC car in autonomous control is the 50 pulses per second Pulse Width Modulated simulation of the RC Receiver to Electronic Speed Control signal. Doing this job in background with one Interrupt sounds correct.

The oscillator seen by TMR0 with pre-scaler runs at 1000000Hz

The pre-scaler 1:256 cuts that down to 3906.25. ie 4kHz.

A post-scaler of 1:64 cuts this down to 61.035Hz. Close enough is my guess. I don't have a grip on how to code this yet. Do I at least understand the concept?

-----------------------another way---------------

Bruce suggests counting up to 20,000 in bits of 1 microsecond. That should be easy enough with a 16 bit register built from TMR1H and TMR1L.

------------now how do I get only one PWM pulse?----------------

Page 135 of the PBP manual seems to indicate that the command:

PWM Pin,Duty,Cycle

will produce "Cycle" number of pulses. It says, "This PWM cycle is repeated "Cycle" times." It also says that, "If a 4mHz oscillator is used, each "Cycle" is about 5ms long."

This seems to mean that the following command:

PWM 1, 75, 1

would produce one pulse about 1.5msec long. This is the neutral pulse for a ESC.

If this is true then writing a routines to control the drive wheels and the steering servo will not be difficult at all.

What do you think?

Ken

[Kenjones1935]

I can count up to 60,000 micro seconds using Bruce's mechanism. This is long enough to make the LED on PORTD.0 blink visibly!

Next step is to add the PWM command and connect the output to my RC car's ESC box.

Thanks again, All

Ken

[Bruce]

This is pretty crude, but see if it does what it should when changing to Forward, Back, etc
with your ESC.

    DEFINE OSC 4

    Match VAR WORD
    
    Forward CON 1000     ' ~1mS pulse
    Neutral CON 1500     ' ~1.5mS pulse
    Back    CON 2000     ' ~2mS pulse
    
    Match   = 20000         ' 20,000 * 1uS = 20mS until compare match
    CCPR1H  = Match.HighByte' Load compare register high
    CCPR1L  = Match.LowByte ' Load compare register low
    CCP1CON = %00001011     ' Compare mode, auto reset Timer1
    
    '/ TRIS & Port Setup
    PORTB.0=1
    TRISB = $FE  ' PORTB.0 output, rest inputs
    
    '/ disable interrupts
    INTCON.7 = 0 ' Disable global ints
    INTCON.6 = 0 ' Disable peripheral ints
    PIE1.0   = 0 ' Disable Timer1 int
    PIE1.2   = 0 ' Disable CCP1 int

    T1CON = %00000000 ' Timer1 off, internal clock, 1:1 prescale
    TMR1H = 0         ' Clear Timer1 high
    TMR1L = 0         ' Clear Timer1 low
    
    T1CON.0 = 1  ' Turn on Timer1

LOOPS: ' NOTE: PIR1.2 is the CCP1IF compare interrupt flag bit.
       ' this bit is set when Timer1 reaches the value in
       ' CCPR1L & CCPR1H
    IF PIR1.2 = 1 THEN   ' If CCP1 to TMR1 compare match occured
       HIGH 0
       PAUSEUS Forward   ' change this to Neutral, Back, Forward to see effect
       LOW 0
       PIR1.2 = 0        ' Clear compare interrupt flag bit
    ENDIF
    GOTO LOOPS

    END

[Kenjones1935]

Not only does your code work (with a couple of adjustments specific to my PICkit 2 setup) but it also makes my car go not-so-fast, faster, and fastest.
It also successfully drives the steering servo left, center and right. This validates the rumors that I was getting from the RC people about the shape and timing of their PWM signals.

GREAT!! Now on to bigger and better stuff like light sensing and proximity sensing. First I need to write some car control routines

FORWARD speed,duration
BACKWARD speed, duration
STEER_RIGHT ?
STEER_LEFT ?



Ken

[Kenjones1935]

Am I correct in thinking that PAUSEUS stops the PIC.

To run my car the PIC must control steering and wheel rotating. It also monitors whether channel 3 from the RC receiver is calling for a return to RC control.

Meanwhile the car must be able to sense and react to light, ultra sound proximity, and other timers. It has to find its way to a destination.

The PWM pulses are generated at 50 per second. That is 20ms between clock matching interrupts. The longest PAUSEUS is 1.75ms which is 8.75% of total time. Steering concurrent with wheel rotation could consume 17.5% of compute time.

Is this a problem? I just don't know enough about real time PIC coding to know the answer. What do you all think?

Ken

[mackrackit]

PAUSE puts the code into a loop for a certain amount of instructions. It does not stop the hardware interrupts.

This is what a PAUSE in ASM looks like. Just a routine to eat some time.

; Delay = 0.1 seconds
; Clock frequency = 4 MHz
; Actual delay = 0.1 seconds = 100000 cycles
; Error = 0 %
Delay	;99993 cycles
	movlw	0x1E
	movwf	d1
	movlw	0x4F
	movwf	d2
Delay_0
	decfsz	d1, f
	goto	$+2
	decfsz	d2, f
	goto	Delay_0	;3 cycles
	goto	$+1
	nop		;4 cycles (including call)
	return

[Bruce]

If you have hardware interrupts enabled, it will jump out of any code routine, execute whatever code you have in your interrupt handler, then return to where it was prior to the interrupt.

Note I wasn't recommending you use this routine to control your motors, I was just curious if it worked. Once you know what you'll need to do to handle all the other things you need to like light sensing, ultrasonic, etc, then you'll have some idea of how to incorporate all your routines (or most) into a single interrupt handler.

Your particular type of application could also benefit from a few dedicated application specific ICs like maybe some 8-pin PICs programmed to do nothing but generate your motor control signals by just monitoring a few inputs, and using these inputs to determine speed, direction, etc. Then you main controller could control motors by just taking a pin or 2 high or low.

A lot of robotics applications use distributed processing like this to take some of the repetitive tasks off of the primary controller.

Example: Instead of using a sonar sensor, you could build this into your main controller. But then your main controller wastes a ton of time doing what the external sonar sensor does.

So - most people will just buy & use a sonar sensor rather than design it into the main circuit. Just take that a step further, and make your own 8-pin servo controllers.

If you have a lot of things going on, motors, sensors, measurements, etc, etc, you can take a huge burden off the main controller by just creating a few of your own litle application specific PICs with a few I/O-pins on the primary controller telling them what to do.

You could have a whole herd of little 8-pin PICs interfaced & controlled by the primary controller, and it only takes a few pins on the primary to control them, and just a few instruction cycles to make that happen.

Or you could shove it all into just one with some crafty interrupt handler to sort it all out. Just an idea. Sounds like a fun project.

Microchip has a new 8-pin PICs coming shortly with a hardware USART & other goodies that could make some really interesting little peripheral controllers.

[Acetronics2]

Microchip has a new 8-pin PICs coming shortly with a hardware USART & other goodies that could make some really interesting little peripheral controllers.

Hi, Bruce ...

Could you give some little details ... please ??? a number ???

I have been DREAMING of it for so long !!!

Alain

PS: 1822 ???

[Bruce]

Hi Alain,

Yes. It's the 8-pin PIC12F1822.

 Enhanced Mid-range Core with 49 Instruction, 16 Stack Levels
 Flash Program Memory with self read/write capability
 Internal 32MHz oscillator
 Integrated Capacitive mTouch Sensing Module
 Data Signal Modulator Module
 MI2C, SPI, EUSART w/auto baud
 ECCP (Enhanced/Capture Compare PWM) Module
 Comparator with selectable Voltage Reference
 4 Channel 10b ADC with Voltage Reference
 25mA Source/Sink current I/O
 Two 8-bit Timers (TMR0/TMR2)
 One 16-bit Timer (TMR1)
 Extended Watchdog Timer (EWDT)
 Enhanced Power-On/Off-Reset
 Brown-Out Reset (BOR)
 In Circuit Serial Programming (ICSP)
 On Board In-Circuit Debug
 Wide Operating Voltage (1.8V – 5.5V)
 Low Power PIC12LF182x variants (1.8V – 3.6V)
 Standby Current (PIC12LF182X):  30 nA @ 1.8V, typical

[Kenjones1935]

Guys and Gals,

I might take a side trip to a scenic view along this road.

Here is a pointer to a BASIC (which BASIC I do not know) program that controls a toy level RC car. Toy levels have no Electronic Speed Control. The DC motor and servo are driven by direct current controlled by four DPDT switches. (Bang-Bang: full speed forward, full stop, full speed back.) This project has only autonomous control. The radio receiver has been eliminated. These simplifications plus the fact that the details are on the WEB make this diversion very tempting.

http://letsmakerobots.com/files/wall_racers.bas
and
http://letsmakerobots.com/node/928

I have an appropriate RC car.
I have a spare PICkit2.
I need to translate wall_racers.bas into PBP.
I need to adapt the resulting ASM to my 16F887.
I think I have enough proto. parts for both projects.

My ego needs a boost.

Ken:

[mackrackit]

Ken,

You are kind, intelligent, and I hear good looking.

There is your ego boost

Your new approach does sound like a good way to start. Save the PWM for later and work on the other parts.

You may want to think about what Bruce said and go "modular". Then when you do get back to the PWM part it could live on a separate chip.

You said you have some solder-less breadboards, so you could get a few of the 8 or 14 pin chips with ADC to play with. Remember MicrChip has a samples program so you could get three from them to start.

[Kenjones1935]

On the other hand==>

Look at this great oscilloscope-like picture of the PWM pulses (fifty per second) very close to 1.75ms long created by Bruce's PAUSEUS technique. I finally figured out the Analyzer part of the PICkit 2 Logic Tool.

Ken

[ScaleRobotics]

On the other hand==>

Look at this great oscilloscope-like picture of the PWM pulses (fifty per second) very close to 1.75ms long created by Bruce's PAUSEUS technique. I finally figured out the Analyzer part of the PICkit 2 Logic Tool.

Ken

Now that's progress! Great job Ken. That a pretty nice looking scope, and the price makes it look even better!

Now you can see what you are doing .... er (or not doing).

[Kenjones1935]

Fritsl's code compiles and runs on my PICkit2.

The proximity detector (Devantech SRF05) responds with different size pulses (depending on the distance from it to an echoing object) when queried by this code.

Next to prove out control of the four DPDT switches which steer DC to the motor and to the servo, destroy the toy car by ripping out its radio receiver. and figure out how to mount the PICkit, the switches board and the two SRF05's.

Question. Is there any way that I can read through the PICkit programmer what is happening in real time to some of the variables. How do I think about adding debugging code?

Ken

[ScaleRobotics]

In case someone wants to measure multiple RC channels with one CCP1 pin, I did a small expermiment. If you connect every other RC receiver channel to CCP pin using 1N914 diodes (or similar), you will be able to measure pulses from three (or four) RC channels using one pin. Without the diodes, the RC channels that are low, ground out the one that is trying to pulse.

Here is a picture of RC channels 2,4, and 6. Without a channel space between them, they stay high. So, with a PIC that has two CCP pins, you should be able to read all 8 channels!

This picture shows scope yellow probe (rc 2, 4, and 6) with their diodes attached to the scope probe. and scope red probe directly attached to RC channel 2.

[ScaleRobotics]

Come to think of it, using one CCP pin, you can decode (however many channels your RC transmitter has - 1). So, using a 6 channel transmitter, you can decode 5 channels using a chip with a single CCP compare pin. To do this, connect RC1, RC3 and RC5 channels from your receiver to the CCP pin with some diodes, and a pulldown resistor. Then capture every transition with capture. The in between pulses are RC channels 2 and 4.

Now to write some code...

[Kenjones1935]

Individually the parts of the system seems to pass their tests.
The DPDT switches worked according to their truth tables.
The proximity switches echoed what looked like sensible responses.
The wheels turned and the steering responded as the DPDT switches asked of them.

However, the car does not work as a system. The PIC is running. The proximity sensors have LED's that blink when pulsed. These work. After a while the proximity detectors stop. All this is in the code, but the steering does not move at all. The wheels do not reverse when something is seen to be right in front of the car.

Question is: What kinds of debugging power do I have once the code is in the PIC besides the Logic Tool Analyze mode?

Ken

[Archangel]

Question is: What kinds of debugging power do I have once the code is in the PIC besides the Logic Tool Analyze mode?

Ken

You can hook up a serial LCD to the system and use debug to send the value stored in your variables, you can store port status in a variable and debug too.

[ScaleRobotics]

I made some progress with 5 channel PWM measurement using a single pin. Curently 5 RC channels are being measured using capture on a PIC12f683. Right now, only one channel is being passed through, but it is possible to get a max of 4 channel pass through on this chip. Bruce gave me the idea of measuring all 5 channels on one pin with his remote code learning thread: http://picbasic.co.uk/forum/showthread.php?t=12555

I need to work on getting channel 1 to be recognized as channel 1. Somehow, I need to check for a low on CCP1 for 3ms or so (between channel 5 and channel1). Anyone got a suggestion on how to do this?

Right now, you have to restart the circuit a few times to get channel 1 output to be channel 1 input. It sometimes selects channel2,3,4 or 5 (depends when you turn the chip on, and which rise it sees first). But the output now is pretty rock solid, no jitters.

I tried to label my ASM pretty well, but I need to work on this overall, especially the variables.

total words used = 275

http://scalerobotics.com/PWMpassthrough.html

[Acetronics2]

Hi,

Ok, it's not PBP ... But it does the trick.

http://www.rcgroups.com/forums/showthread.php?t=576165

Alain

[ScaleRobotics]

Hi,

Ok, it's not PBP ... But it does the trick.

http://www.rcgroups.com/forums/showthread.php?t=576165

Alain

Thanks Alain (was that for me, or Ken??),

But I currently am able to encode 1 channel while decoding 5 channels with the below code:

http://scalerobotics.com/PWMpassthrough.html

And soon should be able to add 3 outputs, and have 4 encoded channels out, while decoding 5 channels in with the pic12f683 (and 3 diodes).

But, what I can't get my head around is how to ensure the CCP1 interrupt starts the first time on RC channel 1 (first pulse). It needs to look for a low of 3ms or so, to ensure channel 1 is looking at channel 1.

Oh .... and I need to do this in ASM.

Thanks for any help you can offer.

[Acetronics2]

Hi,

Sorry ... I didn't verify the link ... ( Xtal wrote both enc and dec ...)

those ones are real decoders

Alain

[ScaleRobotics]

Thank you very much Alain, just what I was looking for!

Need to see how they do their "sync gap", but I notice he has a number of other enhancements as well ... interesting.

Walter

[Kenjones1935]

Thanks everyone for working on the RC PWM problems.

Meanwhile I have built a autonomous toy car from the ideas voiced by fritsl in Lets Built Robots.

The DPDT switches work. I have two separate battery packs. The power for the servo and the wheels shares nothing with the power for the PIC and other logic. Not even the ground circuit! This should keep the noise down.

I am using the LED's on the PICkit2 to help debug. At least I can know which routines have been visited. I wish I could figure out a way to know what are in my variables. The USB programmer can read and write all memory locations. Where do I read about real time debugging?

Oh, yes, my new PIC16F887 book arrived via air mail at the Fitchburg, MA Post Office. It is published by MIKROELEKTRONIKA d.o.o in Belgrade, Serbia. How small the world has become.

[Kenjones1935]

That's the word I have been looking for.

Is there a mechanism in PBP for setting break points.

Once that is done, is there an easy way using PICkit 2 Programmer to read the contents of a particular register?

Ken

[Kenjones1935]

I see in the PICkit 2 Programmer HELP menu discussion of the Debugger tool. Part of MPLAB IDE.

Trouble is, the programmer in MPLAB seems to not get along with the programmer in PICkit 2. I have not been able to make hide nor hair of MPLAB IDE. I have been using Microcode Studio PBP and PICkit 2 programmer.

What am I missing?

KEn