source of voltage near the nextruder?  

RE: source of voltage near the nextruder?

The Love Board filament sensor connector has 3V3 output pin. I suppose you could attach something inline there: https://www.prusa3d.com/downloads/Electronics_drawings/FDM-MK4-LoveBoard-38.pdf

RE:

There is a +5V supply on pin 14 of the large connector (to the main "umbilical cord") on the LoveBoard. The +5V supply also shows up in a few other places on the LoveBoard -- see the attached circuit diagram.

Are you sure about the stated current? 50 µA would be very little for an LED. Might it be 5 mA or (for illumination purposes) even 50 mA = 0.05 A?  In any case, make sure to provide a suitable series resistor to limit the current.

Edit: Ah, hyiger beat me to it... I would prefer the +5V supply, especially if you want to use a blue or white LED; gives you more headroom for the series resistor. 

RE: source of voltage near the nextruder?

Thanks, Jürgen. You are absoulty right. 0.05 A, or 50mA. 

Thanks for the suggestion and the circuit diagram.

Tom

RE: source of voltage near the nextruder?

I was planning to do something similar (bling out the Nextruder) but then it’s going to get removed in a month or two. Let us know how your project goes!

RE:

I'm looking at the schematic that @jurgen-7 linked to, and I see that there is an existing DNF (meaning don't actually add the components) LED circuit on the output of the 3.3V regulator (U1) at schematic coordinates D-7. This means that there should be unpopulated pads for R14 and D3. I'm not sure of the size of the SMT packages, nor their location on the actual board, but they should provide easily(?) solderable places for your current limiting resistor and LED. R14 is specified as 620Ω, and D3 is specified as a red, 2.8V, 5mA LED. (If I remember my formula properly, this circuit would pass ~0.8mA through that LED.) If the location of D3 isn't where you would want it, you could solder fine wires between the pads of D3 and where you want your LED. I'd probably use 30AWG wire, it used to be (and maybe still is) sold as wire-wrap wire. Enameled magnet wire might also be an option (though I find the enamel on magnet wire a little more tricky to reliably remove than the insulation on wire-wrap wire).

Remember, you can pass less current through an LED than its rating. This is one way to dim a LED so it isn't eye-scorchingly bright. The current rating on an LED is the maximum you should pass through it before it starts to get damaged. You may want to play with the LED you expect to use with different resistor values on a bread board to choose the illumination level you want.