Category: Spinal Cord Injury∨g=

DIY Jelly Bean-style Single Switch

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DIY Jelly Bean-style Single Switch is designed for use by individuals with limited upper extremity mobility as a result of neurological involvement.  

Technical Specifications: 

Step 1: Materials.

  • Learning Resources Answer Buzzers (The answer buzzers pack comes with 4 switches, and if you use male-male 3.5 millimeters cables, each one will provide a cable for two switches)
  • 2x Mono (or stereo) 3.5mm Audio Cables
  • Cable Zip ties

Tools used:

  • Soldering iron
  • #1 Phillips head screwdriver
  • X-Acto knife
  • Hot glue gun
  • Wire Cutters/Strippers

Step 2: Disassemble & Inspect.

On the bottom of the switch are 4 rubber feet. Under those feet are four screws. You can use a knife or straight edge to remove the feet. Once unscrewed, you can see that there's plenty of room inside to work with. The switch under here is a very simple, not ultra-high-quality dome switch. The top dome is literally held on with scotch-type tape. You could buy 16 of these switches for every one JellyBean. The construction of this switch, makes it fairly durable. The potential tradeoff in longevity is well worth the affordability.

Step 3: Drill for Cable.

You need to make a hole in the black ring for the audio cable. If you notice on the bottom, there is a registration notch for the bottom so that it only fits into the ring one way. Pick a spot in your ring between the speaker and the battery compartment, on the side where the black/red wires attach to the battery contacts. The author twisted his X-Acto knife while applying pressure to drill a small hole. You could use a drill if you want to but this was just as easy, and the results were good.

Step 4: Strip and Prep Cable.

If you bought Male-Male 3.5mm cables, you can cut each cable in half and use it for two switches. Feed the cut end of the cable through the hole. Strip about 2 inches of the wire, and separate and twist the shield. On the author’s first two switches, he thinned the shield wire as the video recommended, but this made the wire too stiff to route well. Cut the shield wire down to about an inch.

Step 5: Cut Trace.

This PCB trace needs to be cut, disconnected from the circuit in order for the switch to work. Using your knife, apply pressure and a sawing motion to make a break in the circuit board's contact. It wasn't clear from the video, but the switch won't work both as a standalone noisemaker and as an ability switch. Cutting this trace was how the author chose to disconnect the switch from the rest of the electronics.

Step 6: "Drill" PCB.

The author used his hacky spinning-knife trick to drill these holes. It was tried with his thinnest drill bit, but the hole was too large and the drill bit tended to pull the traces off the cheap PCB. Using the sharp knife allowed the author to make smaller, neater holes. Holes are not technically necessary, though I like the mechanical stability they offer. The author also used a 40-watt Weller soldering iron, but was melting/burning the PCB trying to just tack the wires on in the proper spot. The author didn't want to risk damaging the relatively fragile switch.

The author found on some of the switches that the switch's tape covered the spot that needed soldering that provided a positive lead. The author used his knife to push the tape back and scrape the PCB trace to make sure it had a good place to contact.

Step 7: Solder Wires.

Attach the wires to the two places on the PCB you drilled.

Step 8: Strain Relief!

To keep the wires from moving around against their fragile and hacky solder joints, the author applied liberal amounts of hot glue between the wire and the PCB, the case, and even at the point where I had stripped and twisted the shield of the cable. Once the glue hardened, the author added a cable zip tie (about 1/8 inch beyond the edge of the bottom base) to provide strain relief. This will prevent normal pulling on the cable from straining the hot glue joints. Cinch it down tight.

Step 9: Reassemble.

Reassembly is easy, just reverse the first step.

Author:  by RyanFromQA


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Cost of mateirals and supplies.
DIY Jelly Bean-style Single Switch