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Help please ? - Really simple LED circuit

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.

Reply to
pcmangler
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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.
Reply to
Derek Potter

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,

Reply to
Mochuelo

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

Reply to
Deefoo

---------------------------------------------------------------------------------------------------------------------------

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 \\
Reply to
ehsjr

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