Wednesday 8 April 2020

Automatic Hand Sanitizer Dispenser

As I am writing this, the location that I am residing in is under partial lock down due to the Covid-19 pandemic.  Thus I have been confined to home like most folks everywhere throughout the world right now.  Apart from some work via remote working, I have been working on small projects to keep myself occupied.  I saw many posts on automatic hand sanitizer dispenser being shared online past few weeks.  The idea is have a system that can detect a person hand as he/she place it at the nozzle of the hand sanitizer container, and discharge the content automatically, thus avoiding hand contact with the hand sanitizer level to minimize the transfer of the virus or other pathogens to our hand.

  Most of the designs uses an RC servo motor or geared DC motor to activate the nozzle of the container, a few use small aquarium pump immersed in the sanitizer liquid to push the liquid out of the container (when the motor in the pump is energized).  I decided to build one too and I think the solution using the aquarium pump is more elegant and robust.  The RC servo motor/geared dc motor is cumbersome to install and will fail after a few hundreds activation due to the plastic gearbox and potentiometer in the RC servo motor.  However, getting components is difficult at the moment, I do not have the aquarium pump so I have to use whatever material available.  One of the design that interest me is the one that uses a stepper motor with lead screw mechanism to push the level, as seen here, the mechanism is similar to the one used in many 3D printers and CNC machines.  This solution is a bit complicated than the aquarium pump method, but it is very robust, last many cycles of usage and can be easily setup to cater to different container size.  I happen to have some spare stepper motors and lead screw lying around, thus I decided to adopt this method. I share my design below.  I use an Arduino Uno as the controller, and a standard A4988 Stepper Motor Driver module (Alternatively a higher power rating DRV8825 module can also be used) to drive the stepper motor.  I don't have an ultrasonic sensor (for sensing the hand of the user), so I replace the object sensor with a Sharp infrared distance sensor instead.  The design files can be found on the github site.

The construction details:

The wiring diagram:

 A video of the dispenser in action is shown here: