1. Home
  2. Electronics Design
  3. Audio to LED circuit..

Audio to LED circuit..

I'm looking for a circuit that will do the following. It will plug into a headphone jack and will light up an LED when any audio signal is outputted. The brightness of the LED does not vary depending on the strength of the audio output or the volume of the device, it will always be on when there is any audio signal and off when there isn't. I will be sending it short pulses of audio, basically to make it blink at a certain intervals. The specs of the LED are: 1.2VDC 29mA. I'd like to try and use the smallest size battery as possible.

I've done a lot of circuit building, but not much design, so I would consider myself a bit of a newbie. Any help?

Reply to
hurricane_number_one
Loading thread data ...

Most basic idea I can think of right now is to use a comparator to drive an LED.. However this solution may not yield a bright LED.

D from BC myrealaddress(at)comic(dot)com British Columbia Canada

Reply to
D from BC

** Really ??

Even red LEDs take 1.5 volts to make any light at all.

Other colours take higher voltages.

..... Phil

Reply to
Phil Allison

Sorry, forgot to mention it's an IR. Any help on a design?

Reply to
hurricane_number_one

"Phil Allison"

Sorry, forgot to mention it's an IR. Any help on a design?

** Any help on what you are trying to do ?

..... Phil

Reply to
Phil Allison

What about slaving a 74123 off the back of the comparator to keep the LED on for a fixed minimum period. I used this years ago for detecting PCM signals.

Reply to
K Ludger

There are specialty comparators with a latch pin. That can probably help to get a brief 'hold' function.

This helps so the LED brightness in not so dependant on the audio dynamics. (Assuming a circuit that has enough voltage to provide a current for good LED brightness.)

D from BC myrealaddress(at)comic(dot)com British Columbia Canada

Reply to
D from BC

.-------------------------------------------------------------. | This is an ascii schematic, if the diagram appears garbled | | try switching to a fixed-pitch font (courier works well) | | pasting it into notepad works well on ms-windows. | | or in google groups "show original" (in "more options") | `-------------------------------------------------------------'

LED +3v---+--[33R]----->|----------------+ | | +--[1K]--+--[100]--+ + | | | / || | | |/ BC547 in >-----||----|---------+-[100]--| || | |\\ | | \\| 100nF +-->|---+ ~\\ 1N914 | | | | 0V >-----------------+--------------+--

If the LED doesn't light brightly enough try a 1uF capacitor across the C-E of the transistor.

if the LED doesn't get dark enough during silence add a 1K resistor in parallel with it.

brightness may vary depending on the signal, but this should be OK for morse practice etc.

Reply to
Jasen Betts

I'd rectify the signal then low pass and amplfiy to make "minimum" input signal send output to rail. Put output through resistor and LED. One dual op-amp should do it.

George Herold

Reply to
ggherold

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.