Relay Board v1.0



Relays are really awesome electro-mechanical devices. A relay consists of a coil and a switch. When the coil is energized, the switch closes, connecting the two contacts together. The contacts are usually capable of carrying a very high current, whereas the current to energize the coil is much lower. This allows you to drive high currents with low power circuitry. This is a drastic oversimplification, but you can read more on the Wikipedia page.

This board has 2 relays on it that can be used for all sorts of things. The relays on this board are triggered by 12V and the switch can handle up to 160W of DC power at up to 16V. That means these badboys can handle any sort of extruder heater or heated build platform without breaking a sweat. They can also be used to power whatever other high current devices you'd like.

The only major downsides to relays are 1) they have mechanical components which can break down over time. We've estimated the relays will each have a life of about 2000-3000 hours during average MakerBot operation and 2) they make a clicking noise during operation. However, they can easily handle the power and are relatively cheap should they break down.

Get It!


The kit can be purchased from the MakerBot store. It contains all the parts needed to construct your relay board.






The power interface is a standard Molex power connector. This allows you to use a standard ATX power suppy to provide the juice. If you want to hook up your own custom supply, just cut the connector off an old ATX supply and you're golden. Yellow is +12v and Black is GND. Red is +5v and is unused.



There are 2 input channels. Each input is connected to the triggering coil of the respective relay. Each coil is connected to a clamping diode, so its very important to make sure you use the proper polarity. 12V should be connected to + and Ground should be connected to -.

The coil draws about 53mA at 12V, so you'll need some sort of transistor or mosfet to turn it on (such as the ones on the Extruder controller) When the coil is switched on, it will activate the connection and turn the corresponding output on.



There are 2 output channels that each correspond to an input. When the input is energized, the relay turns on and the '+' output is connected to +12v. When the relay is off, the '+' output is connected to Ground. The '-' output is permanently wired to Ground.

Build It

Bill of Materials



The Parts


Step 1: Solder the diodes


Bend over the leads close to the diode body and insert it into the PCB. The polarity (orientation) of the diode is very important. Make sure the band on the side of the diode lines up with the band marking on the PCB.

Step 2: Solder the power connector


The orientation of the power connector is very important. Make sure the inner notches/triangles match the drawing on the silkscreen (they should be towards the inside of the board.

Step 3: Solder the terminals


Make sure you solder the terminals so that the openings are facing the outside of the board.

Step 4: Solder the relays


The relays are pretty easy to solder. There is only one possible way to insert them. The hardest part are the pins connected to ground. You can tell these because the pads are connected to the big ground planes. Make sure to get them nice and hot to avoid dry solder joints.

Use It

Using the relay board is very easy. It is completely transparent to the software, so all you have to do is wire it up. That is a very simple 3 step process:

  1. Connect it to power
  2. Wire it to your extruder controller
  3. Wire it to your output (extruder heater / heated build platform / etc.)

1. Connect it to power


Make sure you turn off your ATX power supply before attempting any of this. Better safe than sorry.

Find an free power socket and plug it into the board. Simple!

2. Connect to Extruder Controller


Note: throughout this guide, we'll use RED wires for Positive and Black wires for Negative.

Connect these to one of the channels on your relay. Don't forget: polarity is extremely important, so don't get it wrong. If you do it will waste current and your relay board will not work.

3. Connect to Extruder Controller to Input


The extruder controller output will be powering the small control coil. The wires in this picture should be connected to the extruder controller mosfet output.

4. Connect Relay Output to load


This step is pretty easy. Simply connect your load (heater, etc) to the output channel that corresponds to your input channel (A or B). The polarity is clearly marked, in case you have polarity requirements on your load (motor direction, LEDs, etc.)

4. Mount to your MakerBot.

The holes are 3mm and the centers are on a square grid 1.7" (~43mm) apart. There are a variety of ways and places on your MakerBot where you can attach it. There is no right way to do it since this is a total hack/mod. Feel free to use whichever way you feel most comfortable with.

Attachment Methods:

  • Drill Holes + bolt on (more reliable long-term)
  • Hot glue (quick and dirty)
  • Tape it to something (ugly but extremely quick)
  • Hang it off the side (EE's across the world are cringing)

Attachment Locations:

  • On the Z stage
  • Above the MotherBoard (on the side)
  • On the top right corner.

Source Code


The design of this board is 100% open source. What this means is that we've released all the CAD files used for parts and the documentation under free licenses. The files were created with EAGLE. There are a few different ways you can access the files:

* Thingiverse - download the source, talk about it, etc.
* Google Code - download the release.
* Subversion - direct link to the release tag.

Unless otherwise stated, the content of this page is licensed under GNU Free Documentation License.