Limited
Limit your design’s range of motion, not your creativity.
Last updated March 2019
A limit switch is a common switch used in design due to its low cost, ease of use, low wire count, and small form factor. You typically see them in a design that has an one axis or more such as a 3D printer, laser cutter, or CNC router, or a camera slider. For example, a 3D printer has 3 axes, X, Y, and Z, so you will have 3 limit switches. Usually they are placed at where the default home location is. Do you ever watch a 3D printer upon initialization? It will first home the extruder by spinning each X, Y, and Z motor until it hits a limit switch. When the limit switch is pressed, a signal is sent to the controller which signifies that the extruder has reaches its home location for a particular axis. Once all three switches have been activated, the controller knows exactly where the extruder is. If you didn’t have any limit switches, the controller would have no idea where the extruder is and therefore, it could start your print in the wrong location.
How do you wire a limit switch? There are 3 wires on a limit switch: COM, NO (normally open), and NC (normally closed). We usually use NO to reduce power consumption since there is no current flowing. When the switch is pressed, the circuit is complete, and current flows from COM thru the NO pin and to your controller pin.You can connect COM to ground or a voltage source such as 3.3VDC or 5VDC depending on the maximum voltage of your controller. We like to connect the COM pin to 3.3Vdc and pull the NO side down (ground). Again, to minimize power consumption. If the NO pin is not pulled down, then this pin will be floating. A pin that is floating could either be 0V or 3.3Vdc which is bad because you can start triggering the controller when you don’t want it to. Even touching the floating pin with your finger can change the voltage level! An example of our wiring is below. This is the NO side pulled low. We also provided a schematic with the NO side pulled high.
In a STEM career, you will get to use your creativity a lot. You could design the next smart and connected city, the next mode of transportation, or a new method of communication. The problems are getting complex so we really need STEM graduates to develop a new way of thinking. How do you develop this new method of thinking? By getting out of your comfort zone. Take on projects that seem impossible at first, jump at a new opportunity every chance you get. You will start thinking in ways you have never imagined. Once you do, you will feel like you could solve anything.
What did we learn?
- Limit switches are used in a wide variety of applications and are easy to use.
- Don’t underestimate your creativity. Take on those projects that get you our of your comfort zone.