Creating a switch for 2 stereo signals

[s_carra]

Hi all, thank you for accepting me.

I have a simple project in mind which I would like to do it with Arduino and maybe a relay. The basic idea is in this picture:

I am a beginner on this, so any input/ suggestion is welcomed. One thing, though: the filtered signal in the drawing should not interfere at all with the straight through path of the original signal.

Thanks,
salvo

[DVDdoug]

A relay is usually the most foolproof solution (or maybe a pair of relays).

The Arduino doesn't put-out enough current to directly drive a relay coil so you need a transistor or MOSFET driver circuit. But you can buy relay boards with a built-in driver.

It usually doesn't hurt anything to feed the signal continuously into the filter so a DPDT relay can handle both channels and either select the direct signal or the signal out of the filter.

Sometimes an unconnected output (or input) can "float up" and then you get a click or pop when it's switched-in. In that case, pull-down resistors (between 10K and 100K) will work with regular line-level RCA connections.

There are "analog switches" and analog multiplexers/demultiplexers but regular-old electro-mechanical relays are simply electrically-controlled and electrically-isolated switches and you are less likely to get noise or distortion or any "weird problems".

[mrburnette]

Relays around audio are "likely" to cause a "pop" which may or may not be an issue for you:

Relay switching for audio - Electrical Engineering Stack Exchange

Additionally, cheap relays have cheap contacts and "may" oxidize causing a higher than desired resistance: not a problem when switching power, but audio signals may not have the ability to create 'wetting' (sometimes: whetting). In the old days, vacuum sealed mercury relays were available and high-end communications often used gold/platinum contacts.

Of interest:
Only Mechanical Relays Will Do For Automated Hi-Fi Audio Source Switching | Hackaday

[cedarlakeinstruments]

If you use a relay, use a reed relay. Power relays aren't very good at switching very low-current signals. However, for this application (switching audio), I've used a DG509 analog switch and found that it works pretty nicely.

[Wawa]

Relays with gold clad contacts are good for audio signals, or reed relays.
Stay away from common relays for power, because they will fail in time (not making contact at all).
If you want to use ICs...
Back in the days I used CD4053 chips for audio switching.
Now I would use the 74HC4053, with a 5volt supply and a negative 5volt supply on VEE.
From memory I used the third DPST switch to mute (short) the unused channel, to reduce cross-talk.
Leo..

[s_carra]

Hi all,

so I got it working (sort of). I have used a 4 relays card and used 3 of them. The signal for the left, right and GRD, are connected to the common pins of each of the DPDT relays, and the unfiltered output is connected to the NO pins and the filtered connection are on the NC pins. On the Arduino, I am using an 5 volts external power supply (2 AMPS rating) that is also powering the Arduino (separate connections). the pins used on the Arduino are A1, A2, and A3 while the 2 LEDs for the unfiltered and the filtered connection, and a change switch which drives the program based on ON or OFF position are connected to pin 8, 9, and 10.

As said this works, but not having used any resistors I notice that when the system is on the NO pin switch the lights on the relays flicker very faintly and very quickly, whereas when the pin NC are engaged the light are on as normal.

The question is: is this normal, or should I add/change something ?

Thanks for your reply.

Cheers,
salvo