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### Topic: DIY EBOW to control LED brightness! (Read 3647 times)previous topic - next topic

#### dataplex

##### Jan 03, 2012, 05:30 pm
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)http://vimeo.com/32643008

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
Ășlfur
-------http://ulfurhansson.com/

#### DVDdoug

#1
##### Jan 03, 2012, 10:31 pm
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.

#### dataplex

#2
##### Jan 03, 2012, 10:50 pm

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

any help would be greatly appreciated!
thanks
-------http://ulfurhansson.com/

#### C4B3Z0N

#3
##### Feb 13, 2015, 04:46 pm
@dataplex I'm developing an idea similar to your project but with radio frequencies and a guitar. I'm wondering if I could pick your brain about what your final schematic ended up looking like.

I'm basing my project off the same schematic as you and have ordered a 8ohm(driver) and 32ohm (sensor) transducer. I would like something like 50ohm to go along with Ivan Kuznetzov build but the next nighest transducer I found was 100ohm.

Any pointers would help!

Here is audio of a very brute and very analog version of my project: https://soundcloud.com/openlapuerta/2n_n3. (in this version all the audio fx are manually manipulated)

#### polymorph

#4
##### Feb 13, 2015, 11:09 pm
It would help if you would draw all your parts to the standard. Is that an NPN, PNP, etc? How is it connected?

Are those rectangles with a black line next to them meant to be coils?

I prefer resistors drawn as symbols rather than featureless rectangles. Remember, a schematic is supposed to be about readability and ease of analysis, or we'd all just post pictorials.

Ah, but here I am, responding to a 3 year old thread...
Steve Greenfield AE7HD
Drawing Schematics: tinyurl.com/23mo9pf - tinyurl.com/o97ysyx - tinyurl.com/q7uqnvn

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