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Picture of Lego Electric Connector
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There are plenty of homebrew Lego sensors and motors floating around, but most use a bisected Lego electric cable or an increasingly sparse electric plates with wire soldered to the bottom.

I, on the other hand, wanted a connector that did not use a preexisting Lego electrical connector. I found a nice (discontinued?) female connector, for the longest time I thought female would be easy to make but then it hit me. Metal studs.

I did find a nice female at http://robotics.benedettelli.com/attachment.htm, but I wanted male For in Brick use

They are unbelievably simple and easy to make, and a large number of Lego electric bricks use male connectors.
I know with the NXT the RCX legacy connectors are all but obsolete, but I prefer them. They look more Lego and are on the RCX, Scout, Code Pilot, Cybermaster, Technic Control Center, Dacta Serial Computer Interface and the 9V train system.
(It is weird a Danish company fits SAE measure better than metric (4.85mm), but it does so I will use only SAE)
3/16 metal rod (I used zinc plated for a good appearance)
A brick that fits the connector or can contain electronics you wish to hook up.
I mainly used 2x4 stud megablocks due to the fact I do not wish to drill into my Legos
 
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Step 1: Pick a Brick

Picture of Pick a Brick
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  I used 2x4’s because that is all I really had and they work for most simple sensors and converters.

  The brick should have at least a 2x2 section of studs if you want a fully rotatable connection (can clip on at any 90 angle) but a 1x2 can be made to work (like the lamp brick).

  Of course a 2x2 flat would make a nice standard cable terminal.

Step 2: Constructing the Connector

Picture of Constructing the Connector
There is no particular order to prepare the connector (except with soldering). But I
  • Drill and hollow out the Brick
  • Cut the rod terminals
  • Solder to terminals*
  • Insert and glue if necessary**
*Due to the heat of soldering you should due the solder work prior to inserting the connectors to avoid melting the brick (believe it or not I did not melt a brick just my hand) If you are building a circuit soldering on lead wires is a must.

**If the drill bit does not slip usually glue is not required (but apply if you see no need to service connector in the future)

Step 3: Drilling

Picture of Drilling
  Drilling is made easy by the fact that, to save plastic, the studs are semi hollow. Without the pilot holes this forms the connector would be incredibly difficult to get right. A drill press is the best for making perfect holes.

  The fastest way to hollow out the brick is a large drill bit down the inner poles as far as possible without drilling the top. Then clear the remaining parts with a rotary tool.

Step 4: Terminals

Picture of Terminals
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To form a stud file and chamfer the end of your 3/16 rod and cut approx. 3/16 length (.2 in was my usual length)

Tinning the wire is easy and will save some frustration.

Tinning the end of the connector takes some time. I first got a glob on the iron and touched it to the unfiled end of the rod. After enough time for the rod to heat up, the glob will flow over the rod end. At that point touch your solder to the rod not the iron and let it flow. At this point, to save time, you could solder on the tinned wire lead.

To insert your new leads just push them through the two holes. I used long nose pliers so I could reposition if necessary. Sometimes going in from the top is easier.

It is best to clip your new connector into a Lego connector and make sure there is continuity. If not use pliers to rotate any lead that is not contacting (always worked for me) then apply adhesive to any loose connector (or all if you wish).

With the wires feed out solder the screw terminal (other connector or PCB) on and glue it into place.

Step 5: The Endless Uses

Picture of The Endless Uses
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Other Potential Uses
Good uses
Nobody makes just a double sided cable (maybe a really long one), these are for homebrew sensors and motors.
  • The LED Brick
  • Micro-motor
  • Other ideas
  • Power Motor Brick
  • Adapter brick
  • Solenoid
  • Sound Brick (original had female connector)
  • 12 button keypad
  • Capacitor pack
  • Switches
  • Battery pack
Active Sensor Uses
What is more fun than simple I/O devices? Making ones with circuitry inside.
  • Linear Hall Effect Sensor (I am waiting to get some SS49E’s)
  • IR distance (just a sharp GP2D120 sensor in a brick)
  • Perhaps with clever programing; Compass, Gyro, GPS, RFID, pretty much anything!

I will eventually make a cable end with male and female terminals

They can even be used on a PIC or AVR powered programmable brick. I hope to see a surge in homebrew Lego electronics.
mrmerino3 years ago
Aww, I'm glad you found a nice female. Although I guess you wanted a male, huh?
GoldCivetta5 months ago

good job using mega bloks instead of damaging LEGO!

You are using mega bloks instead of Legos. Just wanted to clear it up.
jazzzzzz (author)  Loganator123451 year ago
I know, I did not want to drill my Legos.