Electrical stuff question

One of the next projects I am going to work on will involve moving the controller under the deckplates of the printer under the bed, and adding some LED lighting. To that end I have a 12 volt LED ring thing, and a strip of cutable 12 volt LED stuff. I’m thinking that I can just go from the power supply (which will also be under the deck plates at that point) to a switch on one leg, to the strip, to the ring, and back to power supply in a simple serial circuit. Reading around though some people mention needing to add a resistor. Anyone know enough about electronics to help decipher what exactly I need to make sure I don’t catch my LED’s on fire inadvertantly?

The next question, as part of that same electronics move, I will be needing to redo a good portion of my existing wiring harness, and I want to make sure I add disconnect fittings to all the motors and limit switches and whatnot, and the hotend. I’m thinking of using a DB9 serial connector for the hot end piece (or maybe DB15 to accomodate the fan and light leads) but for the Z motors, and sensors and whatnot, I’m looking for a good small fitting with some sort of “don’t accidentally pull apart latch” Any reccommendations on 2 or 4 pin fittings like that, and specifically what they are called? (or part numbers of good ones?) I can crimp pins and build connectors, I just don’t have a clue which ones to pick


First question:
The reason people call for a resistor is because you need to limit the current going into an LED to about 20mA (varies between colors). If you have a strip of LEDs then you need to know how much voltage each LED “uses” when operating. I am assuming you are using a 12v psu. Let’s just say your strip uses 5v and the ring uses 2v (completely made up idk the real values). As I said before, since you want to use a series connection (this may/may not work depending on the specs of the lights) we are going to choose 20mA to be the current (always the same everywhere in series circuit). There’s something called Kirchoff’s voltage law which says that if you move around your circuit in a loop then the sum of the voltage drops (amt. each thing uses) will equal the voltage of the power source. This means that [power supply voltage] - [led strip voltage] - [led ring voltage]- [voltage used by resistor] = 0
So we can find the voltage across the resistor. For my made of values, rearranging the above equation, the voltage drop across the resistor will be 12V - 2V - 5V = [voltage used by resistor] = 5V

Then you need to use Ohm’s Law (V=IR) to determine the resistor’s value of resistance. We know the current through the resistor will be 20mA (cuz it’s the same everywhere) and we know the voltage across the resistor will be 5v so, rearranging V=IR, we can write: R = 5v/20mA = 250 Ohms.

So that’s how you determine which resistor to use if you wish to do this in series. You may not want to do that, though depending on your products. It would help if you had the datasheet or the specs for the LED ring and for the LED strip. Can you point to where you bought them?

Second Question:

The ones used by lulzbot are nice:
CONTACT SKT 14-18AWG CRIMP TIN Digikey 1-66360-6-ND
CONTACT PIN 14-18AWG CRIMP TIN Digikey 1-66361-6-ND
Connector, 4 pin Female housing with latch Molex 50579404 Digikey WM2902-ND
Connector, 4 pin Male housing with latch Molex 701070003 Digikey WM2535-ND

i pasted that from a BOM. It’s got the 4 pin and 2 pin connectors, male and female, and the contacts which fit both.

just reread the OP. If both things are rated for 12v then you will need to connect them in parallel (lmk if you need clarification there). Once again I can give you a good answer if you send me to their source.

So that would look something like this: Wire going from the positive end of the PSU to a switch. The anodes of both LED things are connected to the other end of the switch. The anode is the positive side of an LED (light emitting diode, all diodes are one-way current devices) and the cathode is the negative. So you connect the anodes of the LED thingeymabobbers together and you connect the cathodes together and then they will form two “branches” for the current to flow through and both will get the 12v they are rated for (per your OP). Then you run a wire from the cathodes to the PSU and boom doneskies you’ve got a lightshow.

I still don’t know if you need a currentlimitingresistor (borrowing the linguistic allowances of German for clarity) because I don’t know for sure if they are rated for 12v but if they are then you don’t need to worry about it.

EDIT: if you want some free connectors then you can strip them off of an old computer power supply and tape them together for strain relief.

Thank you for the detailed explanation. Yes, this is a 12V power supply, specifically the one that came with an AO-100. it has 3 12V outputs, one of which is unused. The LED’s in particular are the following:
Input volts: DC 12V (12V 5A for 5meters 3528 600LED light strip) of which I will be using 2 strips of 36 LED’s for the top of the Gantry, and a LED ring http://www.ebay.com/itm/331069300864?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649
which will go around the nozzle. It’'s also definitely 12V, but I don’t know how many amps it draws. the LED’s look identical to the ones on the strip lights, it says “04a” on the package, but that seems low to be amperage (just a guess).

Those connectors look like they should work, I’ll grab some of those. Thanks for the tip!

I went for the 12V RGB LEDs with the controller. I wired them directly into where the power supply connects to the Rambo board. That is what the guys one #REPRAP IRC recommended. In hindsight I wish I had gone for the white as I don’t think the RGB LEDs will be bright enough. I am not going for mood lighting, I am trying to see what is printing!

I just ordered some clear T-Glase to make some LED Gantry. I still have to figure out how to design some sort of gantry around the nozzle since I can’t fnd a stand alone RGB ring that I could tie into the existing controller.

Be careful when moving anything electronic underneath the bed. I’ve been using a MendelMax 2.0 beta that has both the power supply and the controller mounted underneath. While it is not much of a problem for the experienced user, inexperienced users (of which there are many for this printer – it’s in a public-access facility) have a tendency to dump lulzjuice all over (and into) both the power supply and the controller, which, as you might guess, is less than good at best and downright dangerous at worst.

Just my $0.02

Ok these things are just plug n play.
You could plug both into the same 12v source but make sure you do it in parallel, not series.

If you decide to use the port on the controller board then you would be able to switch it remotely which may be more attractive to you than a physical switch. Depends on what you like and your willingness to mess around with the firmware.

Yeah, I can see that being a concern, but 1. This is my personal printer, and 2, the lower chassis will have deckplates mounted shortly that will divert any liquid spill away from the PSU or the location the controller will be at. Any spill would either go down the center hole for the rail and down the two diverter plates, or over the side plates. There will be a fan vent hole somewhere in the side or the top plate, but I plan on putting a raised fan grille on the surface, and mounting it so the fan is somewhat offset of anything that would be adversely impacted by a spill. You can see the deckplates here before they are mounted. The front, rear and side plates are going to be similar once they are done, possibly with some sort of edge treatment (maybe a chrome corner band or something). I keep going back and forth in my mind about adding a belly plate as well, but the end result will basically be two somewhat sealed upside down shallow tubs over the melty electrical bits. Between that and my top secret vibration isolation rubber feet thingies I think that will mitigate the worst of the potential for disaster.

edit: the deckplate project is here: https://forum.lulzbot.com/t/ao-10x-top-deck-cover-plates-and-y-rail-bellows/370/1

Ok, great, thanks for taking a look!

I was planning on using the controller port for the extruder fans someday when I go to a dual extruder. Most of the time they will be on if the machine is on, but I can see times when I will want to have them off, so a simple physical switch should be fine.


Looking forward to a picture :slight_smile:

In the event anyone reads this thread later, it turns out the part number for those pins is for the larger size pins that won’t fit in the smaller sized housings. The correct part numbers may be:
Digikey WM2510-ND
Digikey WM2565-ND

I’ll let you know if they fit for sure when they get here. The other ones are definitly too big though.

FYI, next generation TAZ electronics is happening here:


Very interesting! So the 2 9 pin LCD outputs get ran together to that DB25 serial port, then the extruder 1, 2 7, and x/y to the 4 large cutouts and the bed to one of the two smaller round holes? Very clean, I like it! Those fittings look very interesting too. I’ll have to order a few of them and see how they work with a smaller printer.

I’m going a bit of a different direction with the AO-10x upgrades. I’m treating it more like a computer chassis with a printer on top. I’m moving the power supply inside the lower box frame structure and putting the deckplates on this weekend. From there, the next step will be putting another 20mm extrusion under the deckplate similar to how the Y rail mounted, and using that to mount my controller inside the lower frame, relocating it from the gantry mount since it’s the old RAMPS 1.4. Should be plenty of room to upgrde to a different one in there too though if I ever go that route. The Y motor will also be inside at that point too. That will give me direct wire runs to the Y and Z motors, then I’ll run the bed cables and the X and hotend cables through some Igus Series 6 small cable chains (http://www.igus.com/iPro/iPro_01_0002_0002_USen.htm?c=US&l=en) to elemiinate the cable snag droop issue and run them back to the gantry posts.

For the LCD, i’m trying to pretty much emulate the way you have it mounted on the TAZ. I have a smaller, hopefully working one on the way that should be less of a hassle than that big beast one I never was able to get working without it beeping constantly at me. THe power button will get moved down to the new front cover plate with next to the lighting switch. An always on 120mm fan will cool the electronics box at that point. I’m definitly going to have to borrow that DB25 idea and a couple of those connector ideas from the new Taz build folder though. The Power and USB connections will be on the back plate.

Have you guys thought about putting any kind of extruder docking port on the X carriage? I’m thinking something similar along the lines of the Dell Latitude E-series docking connectors if I can find them somewhere. I think they have about 36 pins on them, so it wouldn’t really be a problem to have a docking socket on the X carriage and a Docking connector on either the single or Dual extruder module you wanted to fit to the X carriage to allow for really quick tool head swaps. A DB9 or DB15 connector might do the trick, but i’ve seen too many monitor pins folded over at work to really want to go that route if I can help it for a connection that is going to be ideally used quite often.(run the single extruder for a job, pull it and add the duals, pull them and replace it with the paste extruder, replace it with a single with a smaller nozzle, etc.) If you run across a connector that would work for something like that, let me know

Thanks for the update!

I think we’ll have a nice metal case for the LCD screen in the store real-soon-now too.

Put me on the list to buy one when you have them then. The one in the pictures looks shiny

Do you happen to have a source for DB25 panel mount to dual DB9 header cables, or are you planning on making your own as you assemble the units? Or are you using some sort of adapter?

We’re going to make those cables. Sigh.


Hopefully you will sell those too along with the cases. I’m going to need both soon. Finally have a working LCD on my printer!

Given what I had to do to get it working, I’d be willing to bet this is one of the few AO-100’s on the planet with a TAZ style full graphic LCD controller attached to it heh.

Also if anyone needs the latest updated firmware for the AO-100 Ramps 1.4 using the current as of today Marlin github distribution, let me know. It seems to be working correctly so far at any rate.