Turn on Your Sound System Automatically While Turning on TV or Computer

In this project, I will create a very simple circuit to turn my speaker system on while I turn my computer on. I found it quite a hassle to turn the speaker on separately each time I sit to work on my computer.

Basically, when we turn our PC on, the USB ports supply a constant 5V and the voltage drops to 0V when power is turned off. I used this property and connected a 6V relay to the USB port of my PC. The relay is connected to the power cable of the speaker. The relay is turned on when pc is turned on and it closes the circuit between mains power and speaker. I hope you will enjoy it!

Tools needed:

1 x USB A, you can salvage it from any unused USB cable or from this link

1 x diode LINK

1 x 6V relay LINK

Some cables, tape and heat shrink tube

If you are using an old USB cable then cut it as shown, the red color wire should be positive supply and the black color is the ground. Another thing is, short the data pins, this ensures a higher current supply from the PC. If the data pins are left open then the highest current output is 600mA whereas shorting the data pins ensures an output current up to 1 or even 2Amps!

Solder the components according to the schematic. The relay is connected in series with the power cord. Be careful while connecting the wires, since 220V can be dangerous and can destroy your device! Use heat shrink tubes to insulate properly.

Connect the diode in the proper orientation. It is needed to prevent the flyback voltage from damaging your device. The coil inside the relay produces a pulse of high voltage while turning off, the diode acts as a protection to prevent this voltage from reaching your device.

Your PC may have ERP disabled, this prevents computer USB ports to turn off even when the computer is shut down. Thus you need to enable ERP from the BIOS setting of your pc. Check this video from Tech Mash for a better understanding: https://youtu.be/FlWKpgkNXKM

NB: this step is not required if you are using the USB port from your monitor or TV.

Use a normal power bank to test if the circuit is working properly before connecting it to the main device. I have used several heat shrink tubes and a double layer of scotch tape to insulate everything properly. It reduces any risk of getting shocked and damaging your device.

Watch the following video to see how the circuit works.