After completing the previous project which could locally or remotely control DC power through the use of PWM. I started to think about methods to control AC or mains power. This of course presents a new set of challenges. First of all, our single transistor used to switch DC previously cannot be used. Second, we cannot use the simple and minute linear regulator we used to provide low voltage for any logical operations.
These are the two main challenges faced when attempting to create a remote alternating current switch. There are of course easy ways around these challenges. To switch AC on and off, we can use a mechanical relay. Using this method, we cannot achieve power manipulation like in the case of PWM with DC switching. This could be achieved with phase angle control using a thyristor, or the like, but for this project, a simple on and off will be sufficient.
To drop line AC voltage for use in logical circuit operations, a small switch mode power supply with an output voltage of maybe 5v could be used. But this is an unnecessarily complex and costly, for this application. A capacitive dropper circuit can be used in this case, which will have a smaller footprint, and be both less expensive, and complex. The circuit will however be mains referenced, which isn’t an issue here, as the circuit will be contained in an isolated case.
The final decision to make will be of how to remotely control the circuit. An infrared receiver was used in the last circuit, but because this circuit needs to be isolated, and because these types of switches are connected to mains power cords which are hidden from view, it was decided that radio frequency would be used. A 433MHz module was selected as there was some familiarity with its use in previous projects.
The circuit board was designed to fit inside an enclosure that previously housed a similar device, which was missing its remote control. Using this enclosure also enabled adequate isolation protection from mains voltages without any additional thought or effort. An RF remote control was also designed, which was powered with a coin cell battery. The ATTiny85 microcontroller was used in both circuits for the logical operations.