Turning Stereo Amplifer on and Off Automatically





Introduction: Turning Stereo Amplifer on and Off Automatically

Do you have an amplifier hidden somewhere in the living room or basement (or home theater) that you want it to turn on when you start to play music?

This circuit is the solution for you!

It is pretty similar to another project I posted a while ago, but here it turns amplifier on and off. If source is playing then the unit will turn amplifier on by using the sending the remote infrared code to turn it on, and when idle for some time, the unit will send the power off remote infrared code to turn off the amplifier. The code here is set to work with a Kenwood 6030 amplifier. If you have a different gear, no fear. Changing the program to work with another set of codes is really simple. You will need to change one or two hex codes only in the KenwoodIdle.PDE file. The best place to learn the codes of your gear is by looking at http://www.lirc.org/ 

The PCB shown in the picture is part of a shield designed for similar idea that also includes Equalizer bar-graph of the music. The circuit here is a subset of it and for it no PCB is really necessary (but since I got 10 PCBs in a batch... I got some spare ones).

Step 1: Parts & Assembly

1x Arduino, any type is good, Uno, Nano, Mini or other mutants.
1x RGB LED (optional)1
1x 330 Ohm Resistor (220 to 470 good as well)2
1x 220 Ohm Resistor (100 Ohm is even better for the IR LED)3
1x IR LED (most likely you need 940nm one)
2x 3.5mm Stereo jacks
4x 22KOhm Resistors (10K is minimum, 56K is maximum I believe)

You will need Arduino IDE 0022 as I did not see the IR Remote library ported to the Arduino 1.x IDE yet.
Put the files in IRremote sub-directory into the Arduino libraries folder
Compile and load the program to your Arduino.

1) Status LED is optional, you don't really need it. but it is useful:
If showing Red, that means amplifier is off and no music is played by source.
If showing Green, that means amplifier is ON but no music is played by source
If showing Blue, that means amplifier is ON and music is played by source.

2) Increasing the value of the resistor of the status LED will make it dimmed which might be desired. I use only one resistor and that means that you can only have one color at a time from this RGB LED. In this case it is by design. If you want to play around with different colors and stuff, you will need to move to three different resistors one for every color. Note that if you do that, the resistors should be slightly different between the Red, Green and Blue ones (for example 330 for Red, 300 for Green and  270 for Blue for the RGB LED that I have).

3) Reducing the value of the resistor of the IR LED can increase the distance between the IR LED and the amplifier under control. Do not go below 100 ohm otherwise you might fry your Arduino. I used 220 Ohm as I placed the IR LED very close to the amplifier IR sensor.

How to connect to your Stereo system:
The amplifier output should be connected to an output of the amplifier, connection to tape recorder is typically not used anymore these days and can very well be the best place to connect this unit to your amplifier (recording output of tape from Amplifier to the Amplifier jack of this unit).
The source input, marked as Sonos in the diagram below (this is almost always the source of music in my house these days) can be taken from RCA connection of the Sonos or using a split cable take one into this unit and the other to the amplifier.

Enjoy the listening.


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Questions & Answers


I'm trying to set this up on a Particle Photon as I want something connected to the network and with my limited knowledge of this stuff it seemed like the easiest way to do it. I'm struggling to understand some things here. You said in a comment response that this has one input (from audio source) and one output (to amp) but I don't understand how the circuit diagram can support that as the L and R inputs (A2 and A3) don't connect to the L and R outputs (A4 and A5). There are connections to resistors that are connected to the ground but how can that connect A2 (L in) to A4 (L out) and A3 (R in) to A5 (R out) as they are all connected to the ground through the resistors. Would really appreciate clarification on this. Thank you!

The Source Input is something that is "input" from this device point-of-view. In my case it simply connects to Sonos player, but that can be CD player, iPod, Tuner or anything else.

The Amplifier Output, is ALSO something that is "input" from this device point-of-view. It can be pre-amp output, Tape recording output from the amplifier or even the speakers (however some change to circuit will be required to ensure no over-voltage is fed to the Arduino analog inputs).

The resistors in the diagram are to ensure impedance of ~20KOhm which is a "standard" impedance on audio line levels. The Arduino has a very high impedance (probably a 1MOhm or more) and this can cause some noise. So the resistors of 22K are simply there to ensure impedance of inputs.

Thanks for your work! I almost made it but i still have some bugs. I powered my arduino (chinese nano copy) from a wall charger and it doesn't work. It works only if i plug it to my notebooks USB port. What can be wrong? (I think notebook give less mA to the board so it is very strange :) )

Can't say for sure. Can be anything from bad wall charger to an electric problem on the power-supply regulator circuit on your Arduino board.

I used cheap USB charges most of the times, either with Arduino or Chinese copies with no issues. Generally speaking prefer those over 7 or 9V wall charges, as it overall dissipates less energy.

Thanks for the instructable! I've got it to work with my old Yamaha rx-v2092. Now I start saving for another sonos.

Glad you found it useful!

Very nice solution! One question though: why do you need to have a second input for the amplifier output? Surely, the source input is sufficient to determine whether:

- if an audio signal is present turn the amplifier on

- if an audio signal has been absent for more than x seconds, turn the amplifier off

I'm a bit confused as to why the second input is required for the stated functionality.


Thanks Ledom.

There is actually only single "Input" but two jacks that are connected. The reason is you take the output from a player, plug it in to this unit and from there take cable from the 2nd jack and connect to amplifier. Pure convinience

curious in anyone did a feasibility study in terms of cost savings than having stereo on all the time? I used a kilo-watt for my stereo which was 35 watts and found 10 month return on investment figuring $25 hardware(resisters free for me), average times used, peak/off peak pricing. $30/year savings.

neat idea! could you also control gain with this remote?