Yet Another Assistive Technology (AT) Button Tester (YABT)

There are plenty of AT (Assistive/Adaptive Technology) Switch Testers out there. Makers Making Change (based in Canada) has some excellent example. I wanted to make my own, using the bunch of 4 AA battery holders I had on hand. So, this is Yet Another Design. Something handy for my toolbox. Perhaps it will give you some ideas -- retrofitting is challenging and cool -- and you're able to leverage items already available in the market.

Supplies

Battery Holder With Switch -- 4 AA

Three LEDs, any type, 5mm are easiest to get.

Three 47 ohm resistors (anything around 50). Supply power is 3.0 volts.

Hookup wire. Heat shrink tubing (optional).

1/8" (3.5 mm) audio jack. Stereo, but mono will work, too. Or TRRS (4 pole).

Step 1: Converting Battery Box

Procure the 4 AA batter holder. These can be purchased from Jameco or other electronics suppliers.

Step 2: Converting Battery Box

Remove the contact (spring) assembly from cells 2 to 3.

Step 3: Converting Battery Box

Remove the positive assembly from cell 4.

Step 4: Converting Battery Box

Insert the positive assembly you removed from cell 4 to the top of cell 2. It should slide right in.

Step 5: Converting Battery Box

You should now have a nice 2 cell battery box. Leaving you two spaces to put your own stuff into. This box will now supply 3 Volts.

Step 6: Converting Battery Box

Remove the spring assembly that goes between batteries 3 and four. You should have two spring/contact assemblies left over for other projects. Those springs are useful!

Step 7: Drilling for Jack

At where battery 3 negative would be, drill a hold which fits your jack. I'm using oversized jacks, so needed an 8 mm hole. You may need smaller. A pilot hole is a good idea. Take it slow, and ream out with a reamer or similar tool to clean up with hole.

Step 8: Check That Jack Fits

Put the jack in the hole and confirm that everything looks good. You will probably need to use some needle nose pliers to clear out any plastic that is in your way.

Step 9: Solder the Jack

Okay, this is going to be dependent on the jack you are using. What you want is left (usually the TIP), right (optional -- usually the first ring), and Ground. Let's talk about Ground. On a Stereo jack, it will be the "shield" -- the base -- the closest to the plastic. HOWEVER , on a TRRS plug (tip, ring, ring, shield) -- the ground is the SECOND RING and the shield is for microphone. I wire to the second ring -- because a stereo plug will still work, and you have the option of using the Mic connection for fancy stuff. It will all make more sense if you look at the jacks and plugs. :-)

Here's where I'm doing some point-to-point soldering magic.

I solder two 47 ohm resistors to the TIP and RING (left and right) connections on the jack. I solder a black (ground) wire to the Ground connection. If you are using TRRS, that's the second ring down. For stereo, it's the shield.

Step 10: Take a Break

And make sure you've soldered the right stuff to the jack. Use a multimeter -- the labeling on these jacks varies widely. Trust your multimeter, not the crumby documentation. :-)

Step 11: Soldering the LEDs

In my case, I'm testing both the tip (left) -- the most common connection -- along with the first ring (right). If you want, skip the first ring (right). I added it Just In Case. For testing, you'll usually just care about the tip.

What I did was place three (or two) LEDs in a Panavise, with all positive leads facing toward me. I bent the leads, and soldered.

Step 12: Drill Some More Holes

After soldering together the LEDs, I roughly took a look at the spacing, and drilled 5mm holes into the battery case.

Step 13: Resistor for "Power On" LED

The two (or one) resistors mounted to the Jack take care of those LEDs, but the "power on" LED still need some help. Solder on the last of the 47 ohm resistors to it's cathode (negative -- what you haven't soldered yet).

Step 14: Point to Point Wiring

Okay, we have two steps here. First, solder the resistors from the jack to the appropriate LED. In my setup, I went Tip (left) to Yellow and Ring 1 (right) to Red -- "red = right" -- my little mantra. I slipped on some heat shrink tubing where I thought things might short out.

All the negatives (from the three LEDS -- left, right, and Power On) get soldered together and shrink tubed. Positive goes to positive and shrink tubed. Cut excess wire as necessary. It's a pretty simple circuit, and I promise to post a Frizing sketch.

VCC > Power LED (green) > drop resistor (47 ohm) > ground -- lights up when powered on.

VCC > drop resistor (47 ohm) > Tip/Left connection on Jack

VCC > drop resistor (47 ohm) > Ring/Right connection on Jack

Ground > Ground Connection on Jack. Is Stereo jack, this is shield. If TRRS, this is second ring.

Step 15: Test It Out

Put two AA batteries in and turn the switch on. Your power (green) should light up.

Step 16: Plug in a Switch

Plug in a test switch and hit its button. The Yellow (TIP) LED should light. Unless it's wired to Ring, where Red (RING) should light. Ether way, you want an LED to light when the button is pushed.

Step 17: I'm Not Lighting Up!

If you are having problems, please let me know. Most likely issues: Don't forget the drop resistors. Remember the polarity of LEDs (long leg = anode = positive). Don't let wires touch. Double-check how your jack is configured -- don't trust the documentation -- test it with a multimeter (a $5 one is fine). You want to check for continuity.

Step 18: You're Done!

This is another little tool I toss into my toolbox when in the field. It allows me to quickly check switches and requires no 3D printing. Some point to point wiring and practice is retrofitting, an you'll be set.