ATtiny servo control

Let's Make Robots
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1 
 

   After a brief discussion with fellow LMR member Maxhirez, about his Hedwig robot,
it seems as though there isn't much support for servos in the ATtiny family of
microcontrollers. After fighting with the 8-bit servo library I found HERE that was
supposed to make it as easy as a standard Arduino to add servos to an ATTiny project,
I decided to start from scratch and create something that was user friendly and Arduino
IDE compatable. Eventually I hope to turn this code into a fully functional open source
library, but until then I wanted to share the code I used to sweep a 9g servo on an
ATtiny84. Here's some code I came up with last night to get a servo to sweep somewhat
accurately that should work out-of-the-box. Future updates should eliminate the delay()
function and support multiple servos. Comments and suggestions are welcome.


              // **** ATtiny Servo Sweep Example **** //

const byte servo  =    0;         // Servo pin on ATtiny
int tPulse        = 4000;         // Total pulse length on 1 Mhz clock 
int hPulse        =   60;         // High pulse time (60=0deg -> 280=180deg)
bool Dir          =    1;         // Servo direction

void setup() {                
  pinMode(servo, OUTPUT);     
}

void loop() {
  digitalWrite(servo, HIGH);                // Set pin high to start pulse
  delayMicroseconds(hPulse);                // High pulse angle data   
  digitalWrite(servo,LOW);                  // Set low for the rest of pulse
  delayMicroseconds(tPulse-hPulse);
  
  if (hPulse < 280 && Dir == 1) hPulse+=10; // Rotate servo to 180 degrees
  else if (hPulse >= 280 && Dir == 1){      // Servo hit upper limit
    hPulse = 280;                           // Keep servo angle in bounds
    Dir=!Dir;                               // Switch direction
  }
  if (hPulse > 60 && Dir == 0) hPulse-=10;  // Rotate servo to 0 degrees
  else if (hPulse <= 60 && Dir == 0){       // Servo hit lower limit
    hPulse = 60;                            // Keep servo angle in bounds
    Dir=!Dir;                               // switch direction
  }
  delayMicroseconds(500); // Give servo some time to move before giving it a new position
}
https://www.youtube.com/watch?v=Dt-z27TL_Hg?hl=en_US
2

More Range

See my article Servo Math and my programs to get full range out of your servos.

3

This works great. How can code be modified to work with Attiny at 8 MHz?

4

When I tried to insert the code to ATtiny 13, I got this error message:

Arduino: 1.8.6 Hourly Build 2018/08/31 05:33 (Windows 7), Vývojová deska: “ATtiny13, 1.2 MHz internal osc., BOD 2.7V, LTO enabled (default)”

Volby pro sestavení se změnily; sestavuji vše znovu
c:\users\kubalovi\desktop\arduino-nightly\hardware\tools\avr\avr\include\util\delay.h: In function ‘main’:

c:\users\kubalovi\desktop\arduino-nightly\hardware\tools\avr\avr\include\util\delay.h:276:40: error: __builtin_avr_delay_cycles expects a compile time integer constant

__builtin_avr_delay_cycles(__ticks_dc);

                                    ^

c:\users\kubalovi\desktop\arduino-nightly\hardware\tools\avr\avr\include\util\delay.h:276:40: error: __builtin_avr_delay_cycles expects a compile time integer constant

__builtin_avr_delay_cycles(__ticks_dc);

                                    ^

lto-wrapper.exe: fatal error: C:\Users\Kubalovi\Desktop\arduino-nightly\hardware\tools\avr/bin/avr-gcc returned 1 exit status

compilation terminated.

c:/users/kubalovi/desktop/arduino-nightly/hardware/tools/avr/bin/…/lib/gcc/avr/5.4.0/…/…/…/…/avr/bin/ld.exe: error: lto-wrapper failed

collect2.exe: error: ld returned 1 exit status

exit status 1