March 16 2016

Our open-source Jellybean Switch has come along by leaps and bounds in the last few weeks, thanks in a big part to Nick Fryer's help in refining the design - thanks Nick!

While Kin, Ade & Nick are all working on improved versions of the design, I wanted to get our existing design production-ready and make some production-quality switches in the process.

We have a collection of switch components, some of them printed on FDM 3D Printers and some printed by Shapeways on industrial printers, so we are curious to see how the design came out on the different printers. 

1. Current Design

The current design consists of 4 components:

  1. The bottom "base"
  2. The top "dome"
  3. An insert that keeps the top and bottom together
  4. A tactile switch

Not shown in this diagram there is also a bit of wire and a 3.5mm plug to connect the switch.

2. Fitting the Top and Bottom

One of the first issues with the current design is that the base and dome doesn't fit together straight out of the printer, you have to sand one of them down first before they will fit. In the case of the Shapeways prints we had to sand A LOT before the prints fitted, so I wanted to see if maybe the design can be adjusted. 

To see what is happening we measured the design size of the prints with the actual print size.

Button Base - Design  vs Print Size

The picture below shows the design size vs the actual size of prints we got from various printers:

To get the tops so that they click freely I had to sand the Top Outside down to 61,5mm and the Top Inside down to 60,1mm. This gives enough room for the top and bottom to move freely, but the button still operates correctly when assembled.

Conclusion

I think we can adjust the top design to be slightly smaller so that it will fit without needing to be sanded down. 

From the measurements the Top Outside should be adjusted from 63,0mm down to about 61,7mm, and the Top Inside from 60,934 down to 60,1mm

3. Tactile Switch

One of the things that have been bothering me about the current design is that we have this big dome trying to push a teeny tiny little area on the tactile switch, so the whole design is very dependent on the dome being printed accurately otherwise it won't click.

There are thousands of tactile switches out there, so I decided to try some other ones that might be more suitable.

The switch that I found works best is shown on the left, it has a much larger surface area to click on, and the surface area is round to fit with our round button

Key Tactile Switch Parameters

As I was looking at new switches they had tons of parameters, so I had to define the key characteristics of our switch: 

  • Activation Pressure - The current switch has an activation pressure of 1.5N (or about 150g)
  • Switch Travel Before Activation - To activate the current switch it is pushed down about 1.5mm 
  • Tactile Feedback - the switch needs to make an audible and sensory "click" as feedback

Pressure Area on Current Switch vs New Switch

The two photos below shows the pressure area on the current switch and on the new switch. The pressure area on the new switch is now in the middle, not off-center, and it is a round pressure area meaning the dome top of the switch is less likely to get stuck

I modified some of the existing bases to fit the new switch, and am very happy with the results. In initial testing it clicked easily and from all directions :)

To work with the existing base design I had to mount the switch 8,4mm from the bottom of the base.

The proposed new switch is available from Australian supplier Element 14 here: