Automatic pencil sharpener

An automatic pencil sharpener machine that works using linear motion. You can sharpen any pencil just by pressing a button and it will take care of the rest, including gathering up all the rubbish into a container.

There is a video associated with this repository/project, I highly recommend watching it before using this repo.

Arduino

You can find the Arduino sketch in the auto_pencil_sharpener directory.

How to upload code to Attiny MCs if needed

• The Attiny MCs can be programmed just like any Arduino and it's very easy to upload code to them.
• You just need a USBASP adapter, then simply make the connections as shown in the image below.

• You will also need to install the Attiny boards using the AttinyCore board manager by placing this link http://drazzy.com/package_drazzy.com_index.json to your "Additional Boards Manager URLs", which can be accessed in File > Preferences.

• From Tools > Board, choose your Attiny board with the no bootloader option.

• Then go to Tools > Programmer and choose USBasp (ATTinyCore), and then press Tools > Burn Bootloader.

• Then to simply upload code, use Sketch > Upload Using Programmer.

• You can use stripboards with some wires to make uploading code to the Attiny MCs more convenient:

Components

• Attiny84, for the micro-controller.
• Nema 17 stepper motor, to drive the linear motion.
• A4988 stepper motor driver, with 100µF-1000µF capacitor across the motor power pins.
• 12V power supply, with at least 3A max rated current.
• LM2596 DC-DC step up/down converter, to convert 12V to 5V. 12V is required for the motors, 5V for the micro-controller.
• MCP1700, 5V voltage regulator, to ensure the Attiny84 has a consistent and smooth voltage. 1000/100µF and 100,000pF capacitors are soldered directly on the MCP1700 to deal with voltage spikes.
• 12V DC motor, the one used has a max speed of 500 RPM.
• IRF3708 MOSFET, to be able to control the DC motor using a micro-controller.
• 1N4004 Diode, to be placed across the DC motor to prevent negative voltage spikes if the DC motor is rotated when the circuit is off.
• Sliding switch, as an on and off switch.
• 2 buttons, to control the stepper motor, left and right controls.
• 8mm L30cm lead screw, for the linear motion.
• 8mm L30cm smooth rod, for the linear rail for the linear motion.
• Pillow block bearing, for the lead screw.
• SCS8UU linear bearing, for the smooth rod.
• SK8 rod support (x2), for the smooth rod.
• D19L25 5x8mm flexible shaft coupling (x2), one to attach lead screw to stepper motor and one to attach pencil to DC motor.

Optional:

• Potentiometer, this will be used to fine-tune the speed of the stepper motor, so it does not move too fast towards the sharpener.

Wiring

Breadboard

Stripboard

3D printing

Please refer to the /3d_printing directory.