next topic »

[on:]

hi guys

i am making an electromagnetic instrument, - basically a harp with 12 ebows on 36 strings. the ebows drive the strings, and are triggered with an arduino.

here is the prototype driving strings on a piano (i am currently building the harp)

i have worked everything out, but i really want to add a neat feature to the device. i would like to add an amber LED to each ebow, which brightness is controlled by the volume of the input signals coil.

here is the schematic i based my ebows on::


so, when a string is vibrating - the signal of the pick-up coil controls the brightness of the led.

can the LM386 drive a single LED by default? how would i implement this into the circuit? whats the most simple way to do this?

thanks!!
all the best
úlfur

[Reply #1 on:]

That should work.   An LED is only going to need something like 50mW.

You'll need to make sure you are driving the 386 hard-enough to get the maximum voltage out of it.  (There is no level/gain control in your schematic.) 

Since the output is capacitively-coupled AC, your peak voltage will be slightly less than half of the power supply to the 386.  And since an LED only lights-up during 1/2 of the AC cycle, you'll need to give it more current (than you would with DC) or accept less-brightness.

I'm thinking you'll need a series resistor of around 100 ohms (but, do you own calculations & experiments).  And check the peak reverse voltage for the LED.    It's probably a good idea to put a reversed diode (or a reversed LED) across the LED to protect it from reverse voltage during the negative-half of the AC voltage swing.

[Reply #2 on:]

i am still a novice at electronics.. but - does this make any sense?

any help would be greatly appreciated!
thanks