What?

Before digging into a project, it's worth thinking about what this thing is and its basic building blocks. What does a hotplate as a product need to do its thing? 

Well, the centerpiece is the heater, a resistive heating element. As the name implies, it's a relatively short piece of wire with low resistance that gets heated up as the current pass through. 

Something then needs to supply the current to it. And something else switch the current on and off to control when we're heating and when cooling. This in principle is a working hotplate, you plug the power, turn the switch on and it heats up. Looking at when the solder paste on top of it melts is enough to know when to cut the power. (yes, yes there are heating profiles, but for the most parts...)

However, we can get more fancy and add a temperature sensor to get real-time temperature feedback. If a smart device, say a microcontroller, reads that sensors and and can control the switch, we get a closed loop temperature-controlled hot plate. So fancy.