Hi there!

I have a small problem with my "weekend" project, I've been working on for almost 3 weeks now. But let's me start from the beginning. I'm not a electronics specialist/technician etc., but I know the basics and have some experience in DYI projects. I'm also a pilot (non-commercial), and got tired of all those cables I have to use in my cockpit in order to listen to some music while flying. So I decided to permanently install a small MP3 player INSIDE my headsets. Everything worked out great. It looks good visually, it works like a charm. With the ANR on inside my room sounds amazing but....

....The tiny-tiny MP3 unit (Polaroid PMP80-2) output power isn't strong enough for in-flight use in a piston airplane. It's just too quiet. So I figured I can hook up a small headset amplifier to it to boost the signal. The level is acceptable and the battery running time too, but there's still one problem I'd like to solve.

I already have 5 momentary switches mounted to the headset to control MP3 unit, and I don't really have a room for more. I'd like to create a small (literally has to be tiny) circuit to turn on the amplifier automatically ON when I'm playing the the music and OFF when the player is off. I could hook up one momentary switch to both, but power-on-off switch on my MP3 player acts also as PAUSE/PLAY button (you have to hold it like 2 sec to turn the unit off).

I was thinking about a couple of solutions:

1) There'a a 3V LED diode that stays lit when MP3 unit is in use. Use some kind of current/voltage/opto sensor to detect when it's on and a tiny relay to switch the power on to the amplifier. Plus I would have to hack the amplifier somehow to stay ON whenever the power is applied to it.

2) Audio signal detector on the audio line to switch the relay on-off.

3) Some kind of switching IC sensing when I'm pressing power off button for 2 sec and turns off the amplifier for me.

I just need a push into right direction and I would be very thankful for more detailed solution to my problem. It has to be physically small, postage stamp size or less.

I included some photos and a simple diagram. (amplifier is the Fiio E5 - not shown on the pictures)

 

2) Audio signal detector on the audio line to switch the relay on-off.

That's what I would use, fed into a level detector with a slow time response (like maybe ten seconds) so it wouldn't incorrectly turn everything off during the dead time between songs.

 

It bugs me when I see the words "relay" and "battery" in the same project, so hopefully "relay" really means "voltage controlled switch."

One trick I oft use is to employ a low voltage regulator chip as a switch. The newer ones come with an enable input. Leave it alone or pull it low and the regulator shuts down. Pull it high and the regulator... regulates. You could use a 5V regulator after the battery to work as a switch to give you something very close to the battery voltage.

Depending on how the LED is driven you may find the correct signal right there to enable the regulator. At worst you would have to add an inverting transistor or fet.

 

Here is a very low current "solid state relay" I made from a 555C timer that latches on for ten minutes when the "SW" node is pulled to ground then after ten minutes it releases and all current goes off.

You could use a comparator detecting audio signal presence to hold the 555 on by pulling the "SW" node low. Change it's timing components (47uF cap and 10MEG resistor) so it times out in ten seconds and you have it done.

 

Thank you guys a lot! That should do it. I'll post the results.