Audio to LED circuit..

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

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

Other colours take higher voltages.

..... Phil

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

"Phil Allison"

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

..... Phil

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.

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

.-------------------------------------------------------------. | 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.

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