Help please ? - Really simple LED circuit

[[email protected]]

Hi, I was wondering if anyone here could help me with designing a
really simple circuit that would illuminate an LED when a signal was
present on an audio input.

Basically, I'm trying to create a "visual metronome" that I can feed
with regular pulses from a minidisc / CD player. Ideally, the LED
would remain lit as long as the signal (sine wave, anything really) was
present and extinguish when the signal disappeared - I could then
control the length of illumination by varying the length of the
recorded audio pulses.

Is this as simple electronics-wise as it is seems (to me anyway !) in
principal ?

Any help would be very gratefully received.

Cheers,

Kev.

---------------------------------------------------------------------------------------------------------------------------
Background Info - I'm a guitarist in a small band and certain songs we
do could benefit with additional accompaniment (a bit of keyboards
etc). I can record these parts myself onto MD/CD, but need to make
sure our human (just !) drummer keeps in sync with the recorded
accompaniment (which would have long gaps of silence). I could record
the accompaniment on the Left channel and a 'click track' of audio
pulses on the Right channel. My idea is then to feed this "visual
metronome" with this signal, and hey-presto, the drummer (and therefore
the rest of us !) can keep in sync with the accompaniment.

 

[Mochuelo]

Yes, the circuit would be very simple, but I would recommend audio
instead of light. This way, the drummer would not have to constantly
look at one point, and with sound it would be easier to distinguish
normal beats from those that start the beginning of a pattern (you
could just use different frequencies). The drummer would wear a small
earphone, or plain headphones (so that s/he could also listen to
another audio track, on the other channel).

If you want to go with the LED, you need a small amplifier (using an
operational amplifier) plus an envelope detector (diode + R + C), or
even just the amplifier alone.

Best,

 

[Derek Potter]

Hi, I was wondering if anyone here could help me with designing a
really simple circuit that would illuminate an LED when a signal was
present on an audio input.

Basically, I'm trying to create a "visual metronome" that I can feed
with regular pulses from a minidisc / CD player. Ideally, the LED
would remain lit as long as the signal (sine wave, anything really) was
present and extinguish when the signal disappeared - I could then
control the length of illumination by varying the length of the
recorded audio pulses.

Is this as simple electronics-wise as it is seems (to me anyway !) in
principal ?

Any help would be very gratefully received.

Cheers,

Kev.

---------------------------------------------------------------------------------------------------------------------------
Background Info - I'm a guitarist in a small band and certain songs we
do could benefit with additional accompaniment (a bit of keyboards
etc). I can record these parts myself onto MD/CD, but need to make
sure our human (just !) drummer keeps in sync with the recorded
accompaniment (which would have long gaps of silence). I could record
the accompaniment on the Left channel and a 'click track' of audio
pulses on the Right channel. My idea is then to feed this "visual
metronome" with this signal, and hey-presto, the drummer (and therefore
the rest of us !) can keep in sync with the accompaniment.

node name components

IN input resistor A 100R
input signal

base input resistor B
NPN base
bias resistor A 1K *
divider resistor A 100R **

GND input ground
NPN emitter
divider resistor B **

collector NPN collector
LED +ve

LED-ve LED -ve
LED resistor A 100R

supply + +5V
LED resistor B
bias resistor B

* nominal adjust to taste
** divider resistor only needed if input is AC coupled.

 

[Deefoo]

Background Info - I'm a guitarist in a small band and certain songs we
do could benefit with additional accompaniment (a bit of keyboards
etc). I can record these parts myself onto MD/CD, but need to make
sure our human (just !) drummer keeps in sync with the recorded
accompaniment (which would have long gaps of silence). I could record
the accompaniment on the Left channel and a 'click track' of audio
pulses on the Right channel. My idea is then to feed this "visual
metronome" with this signal, and hey-presto, the drummer (and therefore
the rest of us !) can keep in sync with the accompaniment.

I used to play in a group that used backing tapes (stereo cassettes). I was
the drummer and I made half of the backing tapes. On my tapes I used one
track for metronome while the other contained the music. On the other tapes
we had the music on both tracks. I then played along with headphones... It
had to be pretty loud though.

--DF

 

[ehsjr]

Hi, I was wondering if anyone here could help me with designing a
really simple circuit that would illuminate an LED when a signal was
present on an audio input.

Basically, I'm trying to create a "visual metronome" that I can feed
with regular pulses from a minidisc / CD player. Ideally, the LED
would remain lit as long as the signal (sine wave, anything really) was
present and extinguish when the signal disappeared - I could then
control the length of illumination by varying the length of the
recorded audio pulses.

Is this as simple electronics-wise as it is seems (to me anyway !) in
principal ?

Any help would be very gratefully received.

Cheers,

Kev.

---------------------------------------------------------------------------------------------------------------------------
Background Info - I'm a guitarist in a small band and certain songs we
do could benefit with additional accompaniment (a bit of keyboards
etc). I can record these parts myself onto MD/CD, but need to make
sure our human (just !) drummer keeps in sync with the recorded
accompaniment (which would have long gaps of silence). I could record
the accompaniment on the Left channel and a 'click track' of audio
pulses on the Right channel. My idea is then to feed this "visual
metronome" with this signal, and hey-presto, the drummer (and therefore
the rest of us !) can keep in sync with the accompaniment.

Something like this should do it.
Adjust the pot so the LED lights at the right times.

+12 -----------+-------+------+------+
| | | |
| | | [470R]
| | | |
[1M] | | [LED]
| | |\4 |
Audio ---||---+-------|---2|-\ |
.1uf | / | }1----+
| 1M \<--3|+/ LM324
[1M] / |/11
| | |
Gnd -----------+-------+------+

Adapted from a post by John Fields - his stuff is always good.
Modified a bit for this application.

Ed