Shredder Auto Reverse

Cheap and simple solution to add auto-reverse to your shredder.  It uses a proximity sensor, an Arduino and a relay to control a VFD (inverter). This is currently alpha and a number of new features will be added in the next week.

Status : Beta (Next update in end Sept.)

Build Time : 4 – 8 hours

Required machines : hand tools

Material bill : 0 – 50 Euro

Compatible machines : Shredder, Extrusion, Shredder & Extrusion Combo



Arduino UNO

Consider buying an Arduino with screw terminals. There are also industrial grade versions.

3 Position Switch

4 Channel – Relay

Proximity Sensor

Magnet & inducting 4 bolts 

Alternative : using a optical sensor

Screw terminals for Arduino 

Amazon (‘Arduino Screw Terminals’). You need this for having good connections.

VFD – Inverter

You may already have this for your 3 phase motor.

Optional Components

Thermocouple for motor heat

Alarm Buzzer

IR Sensor (Recommended) – LM393

24V to 5V Transformer to utilize the VFD’s power supply

LED Push Button to enable/disable Auto-Reverse mode

Screw shield

Wire Diagram – Basic Version with proximity sensor

Wire Diagram – 24V Version with proximity sensor


  1. Download source code or Zip from Github 
  2. Open with Arduino IDE the auto-reverse/auto-reverse.ino file
  3. Upload to Arduino UNO


There are a number of variables which may not fit to your setup. You may increase the the timeout threshold of the sensor. By default this is set to 3000ms (3 seconds). Here are the variables.


  • please make sure everything is grounded and wired as described. It’s easy to destroy any of the components
  • please make sure the shredder box is covered by something
  • for testing, please move the proximity a little away just

Next / Todos

  • Add temperature sensor to recognize motor overheating : done
  • Add alarm sound : done
  • Add LCD & Touchpad to adjust settings
  • Evaluate VFD’s error signal and/or absence of the inverter
  • Update documentation for commercial and safe version
  • Update documentation for Amazon links