In the last blog, I discussed the project that I'm going to build. In this blog, I will describe my experiments with the thermal switches and a video showing the working of the project.
Since my project is to make a circuit to auto-cut off the room heaters, I chose the switches that are triggered around a normal temperature of about 30 deg C and are in the normally closed position. This means, as soon as the ambient temperature of the room reaches 30 deg C, the switch will become open and disconnect the heater from the power supply.
The problem I faced while implementing this is that it is already summer in my country and the temperature is around 40 deg C. So while experimenting with the 30 deg C switches, I found out that they are already in the open position due to external temperatures. Hence, for this experiment, I chose a thermal switch with a higher temperature (90 deg C) and used a soldering iron to heat up the switch to test the project.
Also as suggested by Gough, I did slight modifications in the circuit and went ahead with the switch and the relay only without using the opamp comparator. Since, the switch itself is a binary element (ON/OFF).
Here's a video of the working project-
The challenges in this project are -
The switch does not latch itself in the last position, hence there is a need to design a latching circuit or a timer to trigger the room heater. Once the ambient temperature drops below the switching temperature, the switch changes its position, in my case, it switches back to the closed position thereby switching on the heater again. And this keeps on happening like a loop. So there is a need to somehow put a timer or a latch to hold the OFF state of the switch for a while before it can switch ON again.