https://github.com/chiefenne/attiny85-servo-control

Interrupt based servo control with full 8-bit resolution
https://github.com/chiefenne/attiny85-servo-control

atmel attiny85 avr rc servo-controller

Last synced: about 1 year ago
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Interrupt based servo control with full 8-bit resolution

• Host: GitHub
• URL: https://github.com/chiefenne/attiny85-servo-control
• Owner: chiefenne
• License: mit
• Created: 2018-12-30T08:41:35.000Z (over 7 years ago)
• Default Branch: master
• Last Pushed: 2018-12-31T22:26:16.000Z (over 7 years ago)
• Last Synced: 2025-02-14T05:41:20.662Z (over 1 year ago)
• Topics: atmel, attiny85, avr, rc, servo-controller
• Language: C
• Size: 544 KB
• Stars: 3
• Watchers: 1
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

          

# ATTINY85 Servo Control

[![GitHub](https://img.shields.io/github/license/mashape/apistatus.svg)](https://en.wikipedia.org/wiki/MIT_License)

An RC servo control using an [AVR ATTINY85 microcontroller](https://www.microchip.com/wwwproducts/en/ATtiny85). The control offers an interrupt driven full 8-bit resolution for a standard RC servo. The control is setup via the *8-bit Timer/Counter1* as it offers the the required prescaler (CK/32) to get a 250 kHz timer frequency from an 8 MHz clocked CPU. This allows for approximately 256 steps (8-bit) over a 1 millisecond period.

## Features

 - The servo can be moved to 256 positions within its 1ms-2ms duty range

 - A standard RC servo normally operates a total angle of approximately 90° (+/- 45°)

 - This is done via a 50 Hz PWM signal with a duty cycle of 5% (minimum position) to 10% (maximum position)

 - This means a 20 millisecond PWM signal with a duty cycle of 1 ms to 2 ms

 - To get the full resolution of the 8-bit microcontroller, the *8-bit Timer/Counter1* is setup so that it takes the 8-bit range (256 steps) for the complete duty cycle variation, i.e. 1 millisecond

 - With this setup a resolution of 0.35° per step is possible which is enough for a smooth servo motion

 - A potentiometer can be attached (configured in function *Init_ADC* via the MUX bits for PB3) and used to control the servo position (tested with a 10kΩ potentiometer)

 - An LED attached to LED_PORT indicates the servo center position (use a 200Ω resistor for the LED)

 - The pins for servo and LED can be configured by the corresponding macros (SERVO_PORT, LED_PORT). Do not use VCC, GND and RESET pins

## Example Breadboard Configuration

Obviously, before use, the code **main.c** needs to be programmed on the device via any ISP programmer.

![](images/Fritzing_Layout_1.png)

## Credits

 - The idea was found in the [AVR Freaks Forum](https://www.avrfreaks.net/comment/810846#comment-810846) posted by user **JimK**

## Prerequisites

 - For the code to work the CPU needs to run at 8 MHz (this is NOT the factory default)

 - The fuse **CKDIV8** has to be unset, otherwise the CPU would run at 1 MHz

 - As an alternative the **CKDIV8** could be left as is (factory default), but then the prescaler for the *8-bit Timer/Counter1* has to be set to **4** (using the CS1x bits in the *8-bit Timer/Counter1* control register TCCR1). This alternative is untested.



**Setting of fuses in ATMEL Studio 7 - CKDIV8 unchecked for 8 MHz clock speed**

## Additional information

 - Official MICROCHIP [ATTINY85 datasheet](http://ww1.microchip.com/downloads/en/DeviceDoc/Atmel-2586-AVR-8-bit-Microcontroller-ATtiny25-ATtiny45-ATtiny85_Datasheet.pdf)




Distributed under the MIT license. See [LICENSE](https://github.com/chiefenne/ATTINY85-Servo-Control/blob/master/LICENSE) for more information.