LED bar display for 100v a/c signal (intensity monitoring)

[shahbaz.ele]

dear all
I want to attach LED bar to a TOA machine (Amplifier for audio) for monitoring intensity of signal.
its out put is 100v a/c signal.
can anyone suggest me about it ?

 

[BradtheRad]

The 3914 IC is ideal for bargraph led's. It has ten output pins for 10 led's. You can select between bargraph mode, or having one LED light at a given moment. You can stack them to get a 10 or 20 or 30 led display. It can handle higher volt levels than many popular IC's, although 100V may need dividing down.

It has a cousin, the 3915, which is suitable for audio use because its steps are logarithmic (whereas the 3914 is in linear steps).

Also a 3916 which is a VU meter bargraph.

 

[shahbaz.ele]

but LM3914 is for DC voltage.
will it work for a/c also.

 

[BradtheRad]

I have used a 3914 as an audio bargraph meter. It will respond to the positive waveform only, if you adjust things right. I forget whether I used a diode to remove the negative portion.

You will need to divide down the 100 VAC signal. Maybe via capacitive drop, or inductor drop, or transformer drop. You should choose something that will not affect frequency response. If you use simple resistors then they must be rated for the power dissipation.

 

[shahbaz.ele]

can I do it with induction method.
by induction simple one LED glow for flow of current.
no extra load on circuit.

 

[BradtheRad]

can I do it with induction method.
by induction simple one LED glow for flow of current.
no extra load on circuit.

I once experimented with this idea. I wanted to see if I could get an led to light when the refrigerator called for power.

I used jumper wires to provide one isolated current-carrying wire to the fridge. I wrapped that one wire around a transformer (just a few turns). It did not have any electrical connection to the transformer windings.

I hooked up an led to the transformer windings. I tried the primary. I tried the secondary. One arrangement did cause the led to light dimly, when the fridge called for power. I was amazed I got that much result.

I did not experiment further. To make the led brighter, I suppose I could have tried different transformers, coils, different amounts of windings, etc. It might be worth a try.

If your equipment already contains a coil or transformer, then you might try bringing a coil close to it (with the led hooked up across the coil), and get enough current to light the led.