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Yeah. It’s easy to forget when you’re code steppig that what happens on the screen happens inside the chip about 10 million times faster!!
Hmm… Dead pins. Unless you’ve blasted current into them, how are you on ESD? These chippies are more sensitive than people think.
Holy cow
You’re right! I don’t know why I didn’t think of this. This is exactly the strategy we use for generating a waveform from a lookup table: you don’t lookup every point on the output, rather you lookup the point appropriate to the amount of time which has expired since the last time you looked up a point.
OKay. you may not hear from me for a few days. I’m off modifying my servo controller…!
I might try that routine but
I might try that routine but I still have a problem wiht my SRF05. the old way of measuring the echo pulse will not work since it gets interrrupted. I need to get another method of measuring the echo pulse from the SRF05
Interrupt on change
PORTB usually supports an "interrupt on change." Try implementing that rather than a free running timer.
Have you read about the “capture” method in the CCP module
It may take some reading of the data sheet, but when I used an SRF04 with my PIC18F4620, I used the CCP module. What this basically does is measure the time it takes for a pin to change state. You have to use a specific pin, either pin 16 or 17, and then there are two interrupt options.
1) You get a PING from the sensor on your CCP pin, the timer stops counting, and you get an interrupt.
2) You never get a ping, and the timer overflows, generating a different interrupt.
It may take some reading and some more questions, but it is very accurate and easy to use.
Enthusiast
Why didn’t you show up as a PIC ASM fan before now? I’ve been all alone here for, like, a year…
I’m just slow
I only get a chance to check the postings every few days. Usually, when there is a PIC question, you beat me to the answer. 
I have been using PICs for about 10 years now, all the way back to the 16’C’84.
My first
I started with 16F84 on 30th March 2001. I kept a log book. Sounds uber-nerdy, but it was the right thing to do - with my failing memory.
Still can’t deal with relocatable code and could never get anything generated by Application Maestro to work probperly.
SRF05 problems
I’m trying to measure the echo pulse in a way that I can store its value in an 8bit register that way I dont need to minipulate it inorder to use it in my program. I could compair it to a number and do somethign accordingly. I looked a little into the CCP module but it seems like that will give me a 16 bit value for the range. Its annoying how things that worked stop when you add something seemingly unrelated. I guess without problems like this programming wouldnt be much fun!
edit: for now i have my old routine in a working state but i’d rather use something a little more accurate.
relocateable code
since I am a software engineer, everything I do is relocateable. It makes it easier, in my head anyway, to ‘modularize’ my software for re-use.
well, if you setup your 16
well, if you setup your 16 bit timer to overflow at around 40 mSec, then you can just use the high byte of the timer as your answer ( 8 bits ).
Software Engineering
What do you do? Embedded systems?
I always make reusable subs, but I can’t grasp how you control the location of the GPRs in the modular parts.
my original plan was to use
my original plan was to use the hardware pwm for the srevo but for some reason I cant seem to get it down to 50Hz. the lowest I could get it was about 500 hz. Now I need to figure out an interrupt routine that will work for both the servo and the pwm for the motors. Modifying my routine for the motor pwm didnt seem to work too well. it doesn’t seem to have enough resolution.
I have a 8Mhz internal clock and I need some ideas.
flaky code
I modified my routine for a higher resolution but now the code is flaky. it works for a while then seems to just stop working. I need to modify my routine for measuring the distance with the SRF05 since the interrrupts have made this very inaccurate. I think this is also where my code stalls. I’d also like to figure out a way to reduce the number of interrupts but still have a good resolution so I can get the servo in the right position.
A possibility
Have you tried steppig throught he code witht he "stopwatch" enabled in the IDE?
You may find that the ISR is taking longer to execute than the timeout period.
Multiple MCUs
This statement is puzzling. In 500Hz you have even less time to execute all your instructions, but you calim you have it "down" to 500Hz?
The application which has the limiting feature is teh servos. They MUST operate on a 5 to 20ms cycle time. I would guess that 5ms is too short to get decent resolution on your rotational motors.
I would consider running a 20ms interrupt and using that for both the servos and teh rotational motors.
Another option is to have seperate MCUs. One for the servos, one for the motors (maybe even one for the ping sensor) and put them all on an I2C bus.
Here’s a good
Application note from Microchip on SW PWM generation:
http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1824&appnote=en524189
when I was wrighting about
when I was wrighting about 500hz It was about the hardware pwm. I couldnt figure out how to get a frequency out of that that was less than 500hz. my pic was still using the internal clock of 8Mhz.
my problem is getting a decent resolution that doesnt take up soo many clock cycles
I use a timer for servos
I use a timer for my servos. If you have an 8 MHz internal clock ( I am assuming Fosc = 8Mhz ), then your timers will be driven at 2Mhz ( Fosc / 4 ). However, and this is what I do, prescale your 16 bit timer by 2, so it counts micro seconds. Now you can turn on a servo pin, set your timer to overflow at 1000 - 2000 microseconds, and in the interrupt routine, turn off the output pin. To do the long delay of 20 milliseconds, set your timer to overflow at 20,000 microseconds.
I wish there was a way to attacah a file. I could let you see my servo.asm file which controls 4 servos on an 18F4620.
I’d like to see how that
so do you set the same timer for both parts? set it for the short pulse and then set it for the longer delay. In the interrupt service routine how do you know if you are setting the timer for the short pulse high or the longer delay low? I’m assuming that this method should work to create more than one pulse.
I’d like to see how that works with 4 servos. could you possibly email me the file? my email is snowfortbuilder {at} gmail <dot> com
