Published on November 20, 2014
Leave no one behind.
Spectacles, phone, wallet, watch. Tablet, keys, pocket knife, camera. Multi-tool. USB cable and charger. Extra batteries. Outgoing mail. Coupons, tickets, medication, and makeup. Sunglasses. Contact lens case and solution. That video game you've been meaning to return. A book to read on the subway.
Nowadays we've got more stuff than ever, and it seems like we have to carry most of it around with us. We're also more distracted than ever, our attention constantly jumping back and forth between real and virtual space. It's an insidious combination that can lead to lots of wasted time and energy when we find ourselves at the pharmacy without the prescription, at the hotel without the phone charger, or at the airport without the passport.
Whatever it is you keep forgetting, this project can help. It combines a selection of parts from littleBits' Premium Kit with a few common pieces of off-the-shelf hardware to create an automatic pick-me-up-and-take-me-with-you machine. Put it on a table by the door, put the stuff you want to remember inside, and turn it on. If you start to go out without pickings up your things, it sounds an alarm to remind you to grab them, and keeps ringing until you do.
How it Works
The top tray is hinged and counterbalanced with a tension spring adjusted to just support the weight of the tray itself, but nothing more. When weight is added to the tray, it falls slightly on its hinges, and a "bumper" attached to the right face activates the roller switch Bit on the base. The roller switch turns on the first LED bit (to give a visual indication that it's working) and the sound trigger (to listen for someone approaching the door). When the sound trigger goes off, it sends a signal to the vibration motor Bit, the pulse Bit, and the second long LED Bit. This causes the vibration motor to shake a jingle bell (producing an auditory alert) and also flashes the second long LED via the intervening pulse Bit (producing a visual alert). Because the bell is positioned right next to the sound trigger, the auditory alert creates an "infinite loop," retriggering the alarm circuit over and over again until the weight is removed from the tray, the return spring pulls it back up, and the roller switch resets.
NOTE: This project requires a lot of drilling. The easiest way to get all the right holes in all the right places is to download my full-scale drilling templates, print them onto full-page adhesive backed mailing labels, cut them out, and stick them to the sides of the trays. Then just drill through template and plastic together, starting all the holes with a 1/8" brad point bit, then switching to your step bit to expand them out to finish diameter.
Slide a shelf support into the back right corner of the top tray, and mark the location where the pin hits the wall. Drill a 1/8" pilot hole in this spot, then drill it out to 1/4" with the step bit.
Mark through the hole on the other face of the shelf support to locate the hole for the mounting screw. Drill a pilot hole here as before, but this time only drill out to 3/16" diameter.
Install the shelf support in the corner of the tray, with the pin protruding through the 1/4" hole, using a machine screw through the 3/16" hole. Secure with a flat washer, lock washer, and hex nut. Tighten the hex nut just far enough to compress the lock washer—no need to get crazy with it.
Repeat this step to mount a second shelf support in the back left corner.
Download the base tray drilling templates and print them out at 100% size on an adhesive backed mailing label.
Cut out the template marked "back right upper corner." Remove the adhesive backing, and apply the label to the base tray as marked. Drill 1/8" pilot holes, where indicated, and expand to 3/16" with your step bit. Repeat this instruction with the template marked "back left upper corner."
Mount one of two flat corner braces to the holes you just drilled using a pair of machine screws. Secure each screw with a flat washer, lock washer, and hex nut.
Align the top tray over the base tray, and insert the protruding hinge pin into the uppermost hole of the corner brace you just attached. Repeat the previous instruction to mount the other corner brace, being sure to properly index the remaining hinge pin on the other side. The top tray should now be securely hinged on the base.
Use a piece of carpet tape to temporarily mount the 1-inch "inside L" corner brace to the center back edge of of the top tray's underside. In this position, the protruding arm will limit how far the hinge can open by bumping up against the back face of the base tray. Position the corner brace so that the hinge stops swinging when the bottoms of the two trays are parallel.
With the hinge open to its limit, trace the profile of the corner brace arm onto the back face of the base tray with a marker.
Demount the top tray by removing one of the shelf support pins. Drill a 3/16" hole in the underside of the top tray, using the existing hole in the 1" corner brace as a guide. Since you have a metal "template" to guide your drilling, there's no need for a pilot hole in this case.
Remove the 1" corner brace, peel off the carpet tape, and remove any adhesive residue using a paper towel moistened with rubbing alcohol.
Permanently mount the 1" corner brace to the top tray using a machine screw, flat washer, lock washer, and hex nut.
On the back face of the base, use the tip of your needle file to scratch a line between the traced hole and the midpoint of the short traced edge. Add a second, perpendicular scratch to mark the midpoint of this line.
Drill a 1/8" pilot hole at the intersection of the two scratched lines.
Carefully and patiently expand the 1/8" pilot hole up to 5/8" using your step bit.
Disconnect the motor from the vibration motor Bit at the PCB connector.
Cut the hanging loop off your jingle bell with a pair of side-cutting pliers. Smooth any sharp or rough edges with a needle file.
Pry open the "leaves" on the underside of the jingle bell and pass the motor connector into the bell and out through the hole where the hanging loop used to be.
NOTE: Most jingle bells have a short piece of steel wire inside as a "clapper." The problem with this is that, because the vibration motor is magnetic, the steel will stick to it and not rattle around like it should. To fix, remove and discard the factory clapper, and cut a short piece of 10-12 gauge solid copper wire (which is nonmagnetic) to replace it.
Close up the jingle bell with the motor and clapper inside. Make sure to get the leaves close enough together (without actually touching) that the clapper cannot fall out.
I like to mount Bits using a grid of precisely-placed 1/4" holes that their feet can just pop into. If you do this carefully, the Bits will press-fit and hold securely, but still be easy to remove if you want to use them for something else. It also looks nice and clean. The down side is that you have to locate and drill the holes with a fairly high degree of precision. If you'd rather not go to all that trouble, strips of 1" double-sided foam tape are much faster and almost as secure. If you want to go the foam-tape route, you can skip the template process entirely.
Otherwise, cut out the remaining three paper templates and apply them to the base as shown in the photos and indicated on the template instructions.
Carefully locate and drill 1/8" pilot holes where indicated by the "cross hairs" on the templates. Then expand each of them up to 1/4" using your step bit.
Assemble your Bits as shown in the circuit diagram. Disconnect one end of each of the two "wire" Bits from its PCB connector so you can thread it through the cord routing holes in the case.
Install the "stuff sensing" Bits on the right face of the base tray. Thread the long LED lead and the wire from the wire bit through the routing holes, then press-fit the Bits' feet into the grid of mounting holes. Make sure the roller switch Bit is set to "close" mode.
Install the "door sensing" Bits on the left face of the base tray. As before, thread the "dangly parts" through the appropriate routing holes, then pop the Bits' feet in place. Use the screwdriver to adjust the pulse Bit to its fastest setting.
Reattach the wire Bit PCB connectors to electrically complete the circuit, then install the two daisy-chained wire Bits on the inside front surface of the base. Corral any slack wire inside the base by winding it around the wire bits, or with small twist ties.
Measure and mark a drilling center in the top of the base, about 1-3/16" in from the left hand edge, directly in line with the vibration motor Bit PCB connector. Drill a 1/8" pilot hole in this location, and expand to 1/4" with your step bit.
Thread the connector running from your jingle bell through this hole from inside the base, then run it over to the vibration motor Bit and plug it in. Your jingle bell should now hang inside the base from the vibration motor wires, where it can ring loudly and freely.
Mark and drill two more holes in the top of the base for mounting the LEDs. The location of these doesn't matter too much, so long as the LED leads will reach. I chose to put mine roughly in the center of the front-left and back-right quadrants of the base top. Start with 1/8" pilot holes, as usual, then expand to 3/16" with your step bit. This diameter will be just a touch small for the LEDs, so expand the holes slightly with your needle file until they fit snugly.
Hook one end of your extension spring to the free end of the 1" corner brace.
Route the other end of the spring through the hole in the back of the base, then reinstall the top tray on the base hinges.
Press-fit the pin on your last shelf support into the center hole in the faucet washer, then apply a layer of carpet tape to its other face. With the top tray in the "full down" position, locate and temporarily mount the shelf support on the right side of the top tray with the carpet tape, in a position where the roller switch is depressed by the washer. The switch should be actuated well past its tripping point, but not quite so far that it reaches the lower limit of its travel.
Drill two holes in a horizontal line in the front face of the base tray, right in the middle, towards the top edge, about 7/16" apart on center. Start with a 1/8" pilot hole and expand to 3/16".
Thread the ball chain through the free end of the spring and then through the two holes you just drilled. Connect the two ends of the chain with the coupler, leaving plenty of slack at first.
Use side-cutting pliers to incrementally shorten the ball chain until the spring tension is correct. The hinge should reliably return to its "up" position when the tray is empty, but should fall far enough to trip the roller switch when even a small weight is added.
If necessary, adjust the position of the washer and shelf support until the tray's switching action is reliable and consistent. Once you've got it all working right, drill a 3/16" hole through the carpet tape using the existing hole in the shelf support as a template. Then remove the shelf support and the tape, clean off any adhesive residue, and secure the shelf support permanently back in place with a screw, flat washer, lock washer, and hex nut.
Set the completed project on a shelf or table beside your door, with the sound trigger Bit microphone pointed towards it. Plug in your power source, turn on the power Bit, and put your forget-me-nots inside the tray. The first LED should light up to indicate that the device has detected an object and is ready to trigger when you go out the door. Test it by snapping your fingers or blowing into the microphone, which should set off the flashing LED and ringing bell. Because the bell is right next to the sound trigger, the sound from the bell should reactivate the alarm cycle over and over again, keeping it going until you remove the objects from the tray.
Reset the system by gently raising and lowering the tray, and verify that approaching and opening the door (as you normally would on your way out) also activates the alarm.
If the system doesn't trigger when you go out, or doesn't keep ringing until you remove the objects from the tray, increase the sensitivity of the sound trigger Bit by turning the micro adjuster next to the microphone counterclockwise with the screwdriver.
The littleBits battery + cable will work great for initial testing, but since normal use will likely involve leaving the unit on for hours or days, you'll want to hook up an AC adapter so you can plug into a wall outlet and not drain your battery.
If you have problems with your younger brother, noisy neighbor, TV, or other loud noises accidentally triggering the system when you're not actually going out, try adding a tube of paper and/or tape around the microphone element to increase its directionality. If you still have problems with false triggers, remember you can adjust the sensitivity of the sound trigger by turning the micro adjuster with the screwdriver. Another option is to make your door louder, for instance by adding a shopkeeper's bell or other noisemaker that goes off when you open it.
Finally, you can upgrade your Don't-Leave-Home-Without-It Machine to respond to motion, instead of sound, by swapping out the sound trigger Bit for a motion trigger Bit, which should be a drop-in replacement.