Activate tiny RELAY by headphone jack?? (PLEASE HELP)

[(*steve*)]

I think there would be plenty of power there, harnessing it in a sensible way is a bit of a challenge. You can probably live with an average power consumption under a milliwatt.

I might charge a small capacitor (say 1uF) and use it to power a Schmitt trigger which extends the pulses it receives (essentially straight from the audio). the output is used to switch a mosfet. If this is isolated with a transformer, it should operate as a switch.

The interesting behaviour would be during power-up. As the capacitor discharges, the mosfet will already be off and presumably the Schmitt trigger will have control of its outputs until the capacitor voltage drops below Vgs(th)

it might fail the OP's idea of "simple" though.

 

[supak111]

There is nothing on the market that can do this already? Even if it uses an external power. Can anyone think of anything that could work that I could just buy?

I was able to modify a 12v clapper relay to work but they are just not practical: its too expensive, I have to modify it, and it uses an external power.

Would it be possible to use 2 mosfets? 1 to amplify the sound out of the mp3 player, and second on as a switch?

 

[CocaCola]

There is nothing on the market that can do this already? Even if it uses an external power.

As I suggested on page 1, a LM3915 VU meter circuit could be hacked to do what you want... There are DIY LM3915 kits out there, all you would need to do is interface the relay to one of the outputs... As I stated before it's not the creme of the crop solution but it's one that is simple to get working and understand...

 

[supak111]

As I suggested on page 1, a LM3915 VU meter circuit could be hacked to do what you want... There are DIY LM3915 kits out there, all you would need to do is interface the relay to one of the outputs... As I stated before it's not the creme of the crop solution but it's one that is simple to get working and understand...

Yea that VU meter looks like something I will try, I must have missed that post on the first page sorry.

 

[supak111]

Quick question for every. Would it be easily possible to modify a sound activated LED light key chain finder??

"http://www.dhgate.com/led-sound-con...chain/p-ff8080812bae96f3012bcc9c9e4826a1.html"

If my link doesn't pop up you can ebay "led key chain finder", they are like $1 so it would be perfect.

 

[QuantumCheese]

If were now opening it up to including external power, it becomes quite simple
so yes, probably, with a bit of hacking about.

 

[supak111]

Doesn't look like I'm not gonna make it work easily without the external power so I'm just looking for cheap alternatives.

 

[Lenp]

Don't complicate it!
Use a small audio transformer to step the audio voltage up, then use a sensitive gate triac to switch a low voltage AC relay or optical isolator. Parts cost only a few dollars. I've used a similar design in over a thousand produced units. I can supply details if needed! PM me...

 

[supak111]

I'm not trying to complicate it.

Problem I had was that I was only able to get .07V for the speaker wires, not enough to get the transistor ON. But I ended up make the sound produce .9v so I was able to use just 1 transistor. Ended up being super easy and super cheap.

 

[CDRIVE]

This is my first post here and I'm surprised to see that absolutely no one was curious about what it is that you're switching. So, I'd like to be the first to ask.

 

[wdancer]

This is my first post here and I'm surprised to see that absolutely no one was curious about what it is that you're switching. So, I'd like to be the first to ask.

Yeah, if you are doing it to turn off your speakers when you plug in your head phones, it is pretty simple.

3.5mm audio jack with internal switch in series with the coil of the relay and a small power supply (old wall plug power supply). You are not going to get away from using a power source for your circuit since you need a voltage to turn on your relay.

 

[CDRIVE]

Yeah, if you are doing it to turn off your speakers when you plug in your head phones, it is pretty simple.

.

What makes you think that's what he wants to do? Nothing the OP posted even remotely hints at that. The OP is obviously triggering something.