The approach I’m going to take with this project is to design and build each part of the mains controller as independent circuits and evaluate / play with them. When I have them all hooked up in a way that works and that I’m happy with, then I can draw a schematic and board layout that beings them all together.

In order that my plug in mains controller doesn’t need an extra socket for the power supply I will need to design and build a power supply. Also the invasive power measurement technique that I intend to try out requires two independent power supplies.

As I mentioned in my previous post, a quick look online gives my a simple power supply circuit. Also transformers with two secondary windings are easy to find. This will mean that I have to build the same circuit twice attached to each of the secondary windings.

Below you can see a schematic. You can see that it’s actually two identical schematics. I’ve also added a little LED to each one as a power indicator.

The parts used for this are listed below (Linked numbers are Farnell part numbers).

  • 1 × 9531297 Mini Toroidal Transformer, 1.6VA, 2 × 9V Secondary Windings.
  • 2 × 1621776 Bridge Rectifier 1.5A.
  • 4 × 9451200 470µF Capacitor 25V.
  • 2 × 9666095 5V Voltage Regulator.
  • 1 × 1357320 Screw Terminal Block, 4 Way.
  • 2 × 1142517 3mm Red LED
  • 2 × 9341102 1K Resistor

Next we lay out a board, print, etch, drill it and mount the components. The board layout is below.

A quick check with a multimeter shows that it’s producing 5 volts on both the outputs and that there is no shared ground since no potential difference is reported between 5 volts on DC1 and GND on DC2.