What's the inspiration?
Our project idea was born of the need for a way to heat your food on the go. Since conventional ovens and microwaves are much to large to be casually carried around, we saw fit to create a heating device that was portable.
What can it do?
The user can adjust the potentiometer to set the temperature they want The Hot Box to achieve. The setting temperature will be visible at the left two digits of th LCD screen. The maximum temperature it can go is about 95C, which is enough to bake most cake batters and is well above the temperature most people would heat food to. The heating process takes less than 10 minutes, depending on the termperature settings. We can hold the temperature to within a degree of the set temperature, making it well-suited for those foods that need precise temperature control.
How does it work?
The way that our project works is actually quite simple. Inside a closed box we have a temperature sensor and a heating coil. When the temperature reading indicates that the box is colder or warmer than a set temperature, a relay turns the coil either on or off in order to hold the temperature of the box at a set temperature. The set temperature is controlled by a potentiometer and the set value as well as the actual measured temperature. The enclosure and box are both made of acrylic sheet and a computer power supply provides the power for both the micro-controller and the heating coil.
Fig 1: An overhead view of The Hot Box
What is the most significant challenge we meet?
With the limitation of 5V going through the relay, the heating efficiency on the coil is very low on our very first version of The Hot Box. It tooks way to long to heat up any space and can hardly hold temperature above 50C. With the power supply we decide that we need almost 10A for the coil to head up efficiently, but there is hardly any converter that handles that amount of current. In the most desparate moment, our hero KJ discovered a power-supply for a computer (the big black thing inside the larger box), and he creatively rewired the power-supply to make it suitable for our project. We later shrink the size of the temperature-controlled box so that it hits an astonishingly high temperature of 95C in a surprisingly short amount of time of 5-10 minutes.