Please, how do i control my servo with an ATMEGA 168, 16Mhz MCU

[rox2007]

Once again, please help, please

[robonoob]

u only have a chip? or a whole controll board?
if u have a controll board then search internet for how to make a circuit board with your atmega as its brain and then you can connect ur servos there.
else if u have a control board then where is the problem? just connect the servos where needed and programme it and you are all done
but if u know all the hardware thing(like where to connect it and stuff) and you have done this all (like connecting and powering servo) but you only have problems with servo control code, then you should read some examples of servo controll and read tutorials about controlling the servo with the code you want to use.
anyway internet is a good friend of yours use it

[Admin]

Can you tell us what you have working and what isn't working?

The $50 Robot will tell you exactly how to do it.

Are you sure you have 16MHz?

[rox2007]

Well, this is what i have done.

--i have my mcu board which runs my line detecting code
--i modified my servo for continuous rotation using the admin tutorial. it worked. servo stopped at 1.5ms

this is what i used for delay
courtesy sparkfun blink_iMhz code

//General short delays
void delay_ms(uint16_t x)
{
  uint8_t y, z;
  for ( ; x > 0 ; x--){
    for ( y = 0 ; y < 90 ; y++){
      for ( z = 0 ; z < 6 ; z++){
        asm volatile ("nop");
      }
    }
  }
}

--but i added an oscillator t(16mhz and set the fuse bits) to my mcu after . my code ran perfectly but faster, which is what i wanted
--but now when i try to control the servo with 1.5ms using the above code, it doesnt stop instead it moves slower
--so if anyone can help me with a servo control code, i'll be really grateful

[rox2007]

actually it reverses when it gets that 1.5ms
maybe it recaliberated itself
i should probably run a code from 0ms to 2ms to find the new stop point

[airman00]

perhaps when you added on the 16mhz oscillator you messed up the pulse.

A program that controls a servo @ 4mhz will not work correctly control a servo @ 16mhz

But that is based on my experience in assembly and BASIC , though not in C , thats just a guess.

[rox2007]

yeh, i guess so
i'll just run a code that runs the servo from 0ms to 2ms, and find that centerpoint

[rgcustodio]

check you F_CPU settings make sure you've set it up properly for the new oscillator, then don't forget to recompile your code.

[airman00]

at what oscillator speed did the servo work correctly?

[rox2007]

at 4mhz i think

[rox2007]

check you F_CPU settings make sure you've set it up properly for the new oscillator, then don't forget to recompile your code.

where do i find this

[rgcustodio]

check you F_CPU settings make sure you've set it up properly for the new oscillator, then don't forget to recompile your code.

where do i find this

it should be a define in one of your source or header files.

you should find something like:

Code: [Select]

// make sure the following is the CPU frequency in Hertz
#define F_CPU 1600000UL
in your code.

[airman00]

at 4mhz i think

so try to send it a pulse of 6 ms( 4 times 1.5ms)  in your confused code. Once upon a time , I ran servo code at 8 mhz instead of the 4mhz which worked before. So all I did was double the 1.5  ms pulse , so the microcontroller though it was sending a 3ms pulse , but since it was at 8mhz it ended up giving 1.5 ms.


P.S. If you try to do the 6 ms pulse , have an on/off switch for the power supply , because if you leave it on and it gives a real 6ms pulse i think the servo will turn to the extreme angle and the gears will grind. or maybe the servo won't accept the pulse at all.

[rox2007]

this just might work thanx.

[airman00]

well did it work?

[rox2007]

nope, dont know what happened.....is it possible to loop through numbers and find the right milliseconds for stopping it
actually i think i was running it at 1mhz

[rox2007]

how do you modify the delay_cycles code from atmega8 to atmega16

about the fcpu thing, i dont have it declared anywhere. shouldi declare it?

[rox2007]

it looks like for any value 10ms and above the servo doesnt move, ignore this...it doesnt work

[Admin]

Wait . . . atmega16 or atmega168?

Anyway, you don't have to modify the delay code, its exactly the same.

What changes is the frequency you are running at . . . does your hardware have a crystal built in? Are you using the Arduino or the $50 Robot? What are your fuse frequency settings? Are you using AVRlib?

Here is a great way to determine your frequency for servo use (if you don't have an oscilloscope):

Code: [Select]

turn on LED
loop 10 times:
  delay_cycles(65500);
turn off LED
loop 10 times:
  delay_cycles(65500);
repeat

Now this means that 65500*10*2 cycles occur for every flash of the LED.

Now get out your watch and count the number of times your LED turns on in one minute.

Lets say its 30 times, count.

That means:
65500*10*2*count/(60 seconds) = cycles per second

or

655000 cycles/second

but what you want is to know how many cycles it takes for 1.5ms - the servo control time . . .

so:

655 cycles/ms   ->   655*1.5=982.5

so to get your servo to stop moving, you'd want to send a signal of 1.5ms long, or 982.5:

turn servo on
delay_cycles(982);
turn servo off

Your servo moving one direction would be 655*1 (for 1ms), and the other way is 655*2 (for 2ms).

[rox2007]

i'll try this..

Thanx alot admin, you are still the best

[Admin]

thanks

I think Ill turn that last post into a tutorial . . . it saved me tons of timing frustration when I figured that out last summer . .  .

[rox2007]

that wont be a bad idea

[rox2007]

-----i am using a 16mhz external crystal with an atmega168

-------built like the $50 Robot

fuse frequency settings= i got this from sparkfun

----avrdude -p m168 -P com1 -c ponyser -U lfuse:w:0xE6:m
i am using AVRlib?

admin, one question:
loop 10 times:
turn on
loop 10 times:
turn off

do you mean i should run it in a for loop like

for (j = 0; j < 10; j++)
      {
          PORTC = 0xFF;
         PORTB = 0xFF;
         PORTD = 0xFF;
         
           delay_cycles(65500);
         PORTC = 0x00;
         PORTB = 0x00;
         PORTD = 0x00;
         loop 10 times:
           delay_cycles(65500);
      }


OR

   for (j = 0; j < 10; j++)
      {
          PORTC = 0xFF;
         PORTB = 0xFF;
         PORTD = 0xFF;
      }   
      for (j = 0; j < 10; j++)
      {
         delay_cycles(65500);
         PORTC = 0x00;
         PORTB = 0x00;
         PORTD = 0x00;
         
         delay_cycles(65500);
      }

[rgcustodio]

regarding the F_CPU thing nope i guess it isn't needed in your case, i think you're not using avrlibc. you can ignore the F_CPU thingy.

[Admin]

you want to do that first for loop you posted, but probably just for your LED pin . . . I'm also doing 16MHz on another AVR, so if you did your fuse settings properly, you will find your delay should be around ~800.

since its just a quickie test, I just do:

Code: [Select]

while(1)
{
LED_on();
delay_cycles(65500);
delay_cycles(65500);
delay_cycles(65500);
delay_cycles(65500);
delay_cycles(65500);
delay_cycles(65500);
delay_cycles(65500);
delay_cycles(65500);
delay_cycles(65500);
delay_cycles(65500);
LED_off();
delay_cycles(65500);
delay_cycles(65500);
delay_cycles(65500);
delay_cycles(65500);
delay_cycles(65500);
delay_cycles(65500);
delay_cycles(65500);
delay_cycles(65500);
delay_cycles(65500);
delay_cycles(65500);
}

[rox2007]

i got 521, with the code i wrote. i'll try what you wrote. and was this correct for a 16mhz external oscillator

avrdude -p m168 -P com1 -c ponyser -U lfuse:w:0xE6:m

[rox2007]

maybe i didnt do the fuse settings right, how can i do it right

[rox2007]

Read Osc.Calibration Byte successful: 0xA8 (168)

i got 22 counts
i checked my fuse bits and they are correct

    *  CKDIV8 = 1
    * CKOUT = 1
    * SUT1 = 1
    * SUT0 = 0
    * CKSEL3 = 0
    * CKSEL2 = 1
    * CKSEL1 = 1
    * CKSEL0 = 0

[Admin]

maybe i didnt do the fuse settings right, how can i do it right

I use AVR Studio to do my fuse settings.

i checked my fuse bits and they are correct

    *  CKDIV8 = 1
    * CKOUT = 1
    * SUT1 = 1
    * SUT0 = 0
    * CKSEL3 = 0
    * CKSEL2 = 1
    * CKSEL1 = 1
    * CKSEL0 = 0

how do you know thats correct? are you sure you want to divide the clock by 8 (making it 1/8th the speed)?

[rox2007]

actually, i got that from sparkfun. I am using the serial dongle and thats what i saw on sparkfun's tutorial. well i just skimmed through the tutorial, maybe i missed something. I dont know how to do it with AVR though. If you could help me out that would be great.