# Audio Jack Power

• ### Question

• I am looking into sending code through a Infrared LED that is connected via 3.5mm audio jack.

This would work by turning a current on and off in relation with the binary code.

Could anyone explain how I would do this? Thanks!
Friday, May 9, 2014 2:11 PM

• An audio jack will have a small amount of current that is equivalent to sound output. I don't know how much amperage it has, nor how your LED would work. It would probably be better to have the LED run by an external power source (battery) that works in relation to the sound output of the power jack. (sound = 1, silence =0).

Matt Small - Microsoft Escalation Engineer - Forum Moderator

NOTE: If I ask for code, please provide something that I can drop directly into a project and run (including XAML), or an actual application project. I'm trying to help a lot of people, so I don't have time to figure out weird snippets with undefined objects and unknown namespaces.

Friday, May 9, 2014 7:04 PM
• Hah! Someone after my own heart! EE graduate here (but I only tinker with this stuff nowadays).

From the old Microsoft archive, a headphone jack is expected to supply 300 mV into a 32 ohm load; it should also be able to supply 1V into a 320 ohm load.  A little math says that the audio current is 3 to 9 milliAmps.

But looking here, LEDs generally require 15 milliAmps of current at 3V, which means that you're short both on the voltage side and on the current side.

Jumping right into the Mouser catalog, and picking a dim LED (dim LEDs take less power), we find something like this: they've got a low-current LED that needs 1.7V and only 2mA current.  That's still not good enough.

There are companies like LabJack (which I've never used, but I've read about their stuff) sell USB devices that can run an LED (and much more); they are about \$100.

Or, if you're handy with a soldering iron, you could whip up a simple battery-powered audio amplifier; almost any kind of circuit should work.

Alternatively, if someone else is a bit less rusty than me chimes in, I might have got my figures wrong, and it turns out to be very do-able.

Friday, May 9, 2014 7:58 PM
• You should use a multimeter and see for yourself what Voltage and Current readings are :) I just measured voltage on my Dell Latitude it was running between +0.05 V to -0.02 V.

While math looks OK but a 5V battery will always offer 5V no matter what is your Resistance, any change in resistance will simply increase or decrease current. Any such circuits are designed to handle situations where you may want to overdraw circuit, so there will always be upper limits for current.

Like Matt suggested, you should simply use a Transistor Switch (PNP or NPN) and use the output of Audio jack as a control voltage.

-- Vishal Kaushik --

Sunday, May 11, 2014 5:25 PM

### All replies

• An audio jack will have a small amount of current that is equivalent to sound output. I don't know how much amperage it has, nor how your LED would work. It would probably be better to have the LED run by an external power source (battery) that works in relation to the sound output of the power jack. (sound = 1, silence =0).

Matt Small - Microsoft Escalation Engineer - Forum Moderator

NOTE: If I ask for code, please provide something that I can drop directly into a project and run (including XAML), or an actual application project. I'm trying to help a lot of people, so I don't have time to figure out weird snippets with undefined objects and unknown namespaces.

Friday, May 9, 2014 7:04 PM
• Hah! Someone after my own heart! EE graduate here (but I only tinker with this stuff nowadays).

From the old Microsoft archive, a headphone jack is expected to supply 300 mV into a 32 ohm load; it should also be able to supply 1V into a 320 ohm load.  A little math says that the audio current is 3 to 9 milliAmps.

But looking here, LEDs generally require 15 milliAmps of current at 3V, which means that you're short both on the voltage side and on the current side.

Jumping right into the Mouser catalog, and picking a dim LED (dim LEDs take less power), we find something like this: they've got a low-current LED that needs 1.7V and only 2mA current.  That's still not good enough.

There are companies like LabJack (which I've never used, but I've read about their stuff) sell USB devices that can run an LED (and much more); they are about \$100.

Or, if you're handy with a soldering iron, you could whip up a simple battery-powered audio amplifier; almost any kind of circuit should work.

Alternatively, if someone else is a bit less rusty than me chimes in, I might have got my figures wrong, and it turns out to be very do-able.

Friday, May 9, 2014 7:58 PM
• You should use a multimeter and see for yourself what Voltage and Current readings are :) I just measured voltage on my Dell Latitude it was running between +0.05 V to -0.02 V.

While math looks OK but a 5V battery will always offer 5V no matter what is your Resistance, any change in resistance will simply increase or decrease current. Any such circuits are designed to handle situations where you may want to overdraw circuit, so there will always be upper limits for current.

Like Matt suggested, you should simply use a Transistor Switch (PNP or NPN) and use the output of Audio jack as a control voltage.

-- Vishal Kaushik --