Smart Power Saver Switch. No Arduino, Internet or Programming Required

This is very simple, but very useful home automation device - it tracks power consumption of your main load, and powers on and off additional load according to it. It has many practical uses - like power on your TV, when you power on STB, power off your desk lamp, when your monitor goes to sleep, power off your audio amplifier, when you turn off your TV, and many, many others. There are no hard to get components (actually, 99% of parts used in this project, can be sourced from an old AT/ATX power supply), no SMD parts, no programming, no Wi-Fi and no internet required.

What you will need:

1 pcs LM358 opamp

4 pcs general purpose diodes - 1N4004, 1N4148, almost any will work.

1 pcs general purpose small NPN transistor - S8050, BC547, 2N3904, C9013, etc.

3 pcs 10K resistor (1/4 or 1/6W)

1 pcs 220K resistor (1/4 or 1/6W)

1 pcs 100K resistor (1/4 or 1/6W)

1 pcs 33K resistor (1/4 or 1/6W)

1 pcs 1K resistor (1/4 or 1/6W)

1 pcs 4.7K resistor (1/4 or 1/6W)

1 pcs multi-turn 10K resistor.

3 pcs 10UF capacitors (may be mica or electrolytic, at least 6.3V voltage)

1 pcs 0.1UF mica capacitor.

1 pc 5 volt relay - SRD-05VDC-SL-C or any other similar.

1 pcs input filter from a switching power supply.

1 pc 5 volt power supply, should deliver at least 100 milliamps.

Any empty enclosure of appropriate size, or a sheet (approx A4 sized) of 3mm acrylic.

Generic diy tools, such as soldering iron, hot melt glue, scissors, etc.

Optional components:

Glossy film for diy labels.

Power input/output sockets (ones usually found on AT/ATX power supplies).

Power switch.

The circuit is fairly simple and works as follows:

The current consumed by the main load, goes thru the transformer (Tr1), where it induces small voltage across secondary winding. This voltage is amplified by 1st amplifier in opamp (OP1), rectified (by diode D5), filtered (by capacitor C5) and fed to user adjustable (via changing reference voltage at opamps pin with pot P1) comparator (built using 2nd opamp, OP2), which controls relay (Rel1) via transistor (T1), and relay controls auxiliary load. There are some additional components too - diodes D2 and D3 are used to provide protection of opamp input, in case of spike at circuit input, resistor R8 adjusts delay, after which relay is triggered. Resistor R6 protects opamp's output from overloading and diode D4 protects transistor from high voltage spikes, which occur, when relay is de-enrgized. There are also two 0.1uf bypass capacitors on PCB (not shown in circuit) which are used for noise reduction at opamp's power pins.

The circuit is built on single side PCB, which is designed to be home manufacturing method friendly - by CNC or etching. Of course, you can outsource manufacturing to any PCB manufacturing plant - gerber files are included in the "downloads" section. I've manufactured both versions, as you can see on the photos.

Before starting the assembly, you'll need to modify an input filter. For this, you have to remove one of windings, and wind a new one, using 3-4 turns of relatively thick wire (18 or 20 AWG will work fine). This will be the "input" winding.

I'm using small 5VDC supply for powering the circuit. Current consumption with relay on is about 65mA, so almost any 5V power supply will work.

After assembly is completed, you can test the circuit in the following way. Set the pot P1 into middle position, do not connect load to the circuit, just power it on. If everything is done properly, relay should click and release in couple of seconds. If this does not happens, check your circuit for any errors or issues.

If everything is fine, you can connect your loads - both one to be monitored and one to be controlled. Put your main load into ON state, and by adjusting pot P1, make sure that controlled load is also powered on. Now put your main load into off/standby state (either with remote control or power button or whatever way you do it) and make sure that controlled load also went off (there might be a small delay of 2-3 seconds, before it goes off). If it stays on, adjust the pot in the opposite direction, until aux load turns off. Now wake up your main load and check whenever controlled load also goes on. That's all.

I've made several revisions of this controller, some are "lo-fi", using homebrew PCB and enclosure from old laptop power supply, some of them use standard NEMA boxes (do not forget to make vent holes in the top), and also there is a special, "deluxe" version, which has enclosure made from acrylic and has full sized input and output sockets (taken from old PC AT power supply), power switch, labels and even silicone feet. In this mod, PCB is mounted upside down, so hole for adjustment pot is made from the below - to not ruin the classy look this controller has :)

You can download the archive with the all files from this link. (I tried to attach zip file here, but it does not works)

https://gofile.io/d/Tk3IKE

It contains a folder with files and two standalone files:

\PCB - Folder with Gerber and DRL files needed for ordering PCB manufacturing at companies like expresspcb, jlcpcb and others.

powerman.gbr - Mirrored Gerber file for making PCB at home using engraving or etching.

Shell.svg - Plans for cutting the shell from the acrylic sheet of 3mm thickness. Optimized for K40 and similar laser cutters.