It can take several hours to 3D-print the various enclosure parts. You can get a head start on the assembly process by charging the rechargeable batteries and connecting the electronic components while the enclosures are printing.
This printed list of wiring tables will be helpful during the assembly process. Print it and have a copy on hand.
The Assembly Process
Install and Charge the Rechargeable Batteries
What you need:
- (2) 18650, flat-top rechargeable batteries
- (1) DIY More battery holder
- (optional, but highly recommended magnetic USB charging cable with an appropriate magnetic plug)
- a USB wall plug voltage converter that provides at least 2 Amps at 5 volts
Assemble the parts:
Insert the batteries into the holder as specified on the holder. Note that the + ends of both batteries point in the same direction.
If the battery holder has a sliding switch, move the slide toward the batteries.
Plug a USB charging cable into the wall-plug voltage converter and then into the charging port on the battery holder.
Allow the batteries to charge until all five red LEDs on the underside of the holder are lit and steady. This can take several hours.
This process step is described in the following video:
Deciding on the Location of the Components
It can seem like a chicken-and-egg problem. How do you determine where the components should go if you don’t already have them assembled? But you can make good progress by using the component sizes and your imagination. The proximity sensor enclosures are about 50 mm square, and the control unit enclosure is about 150 mm wide and 100 mm high.
There are two fundamental questions you will try to answer during this step:
- Where will I mount the proximity sensors, buzzers, and the control unit?
- How will I mount the proximity sensors, buzzers, and the control unit?
- How will I route the phone cables from the control unit to the proximity sensors?
What you need:
- The control unit, proximity sensor, and buzzer 3D-printed enclosure components.
- Optional: example mounting clips/cups
- Optional: lengths of Velcro straps
Determining the component locations and mounting options
First, consider where you will want to mount the proximity sensors. You will want to mount them as far forward on the walker or gait trainer as feasible. You will also want to mount them along the outside reach of the walker/trainer. The mounting location must be rigid and offer a wide view, ensuring that other parts of the walker/trainer do not obstruct their view.
Next, consider the typical height of obstructions. If most obstructions will be low to the ground, you will want to mount the sensors lower on the walker/trainer. If obstructions are higher, you will want to mount the sensors higher.
When you decide on a location, determine what parts of the walker/trainer frame are there. Is it a round pipe that would accommodate a mounting clip, or a flat surface, or a set of pipes that would require a Velcro strap? Will the sensor lie along the mounting surface or be placed at the end of a frame element that runs from back to front? Pick a mounting method that works for the chosen location.
The control unit should be placed centrally to the sensors and securely. Now, imagine the best way to mount the control unit there.
Once you’ve chosen locations for the sensors and control unit, take a tape measure and run the tape from the approximate location of the control unit along the walker/trainer frame to the approximate location of each of the sensors and buzzers. If the control unit isn’t centered exactly between the other components, these four distances can be different. Use this information to select the phone cords that you will purchase or construct. Note that you can make your own custom-length phone cords by purchasing a length of 4-wire phone cord, RJ11 phone plugs, and a wire cutter/stripper made specifically for this purpose.
Preparing the Jumper Wires
What you need:
- the four 3D-printed wire clamps
- (15) jumper wires separated into (1) set of three, (2) sets of two, and (2) sets of four
- superglue
Assemble the parts:
Begin by printing the five wire clamps. They will be completed in just a few minutes. Handle them carefully. They’re small and have thin walls.
Arrange the wires in each group with the blocky female ends aligned side by side and with the small metal window facing up and the wires untangled.
Apply a small amount of superglue to the face of each clamp. Then, carefully squeeze the female block ends of the jumper wire groups between the walls of the clamps and onto the superglue. The ends of the blocks should align exactly to fit tightly in the clamp.
Hold the blocks down for several seconds, then set aside the clamps and wires for the glue to cure.
This process step is described in the following video:
Mounting the Raspberry Pi Pico in the Terminal Breakout Board
What you need:
- (1) Raspberry Pi Pico
- (1) Terminal Breakout Board
Assemble the parts:
The pins on the underside of the Pico will be inserted into the two rows of black headers that rise up from the Terminal Breakout Board.
Note that the USB port on the face of the Pico points away from the small, green, 3-screw terminal block.
Angle the Pico up slightly so you can easily align the far row of pins and the openings in the far row of headers. Insert the Pico pins just far enough to ensure alignment and then rotate the Pico down and the near row of pins into the near row of openings.
Verify that all pins are properly aligned with the holes, and then gently press down on the top of the Pico to slide the pins into the headers. The pins should slide in all the way, and the Pico should rest on top of the headers.
This process step is described in the following video:
Attaching the Phone Line Connectors and Jumper Wires to the Terminal Breakout Board
What you need:
- terminal breakout board with inserted Pico
- (1) 3-wire group of “clamped and glued” jumper wires
- (4) RJ11 female connectors
- (1) potentiometer (i.e., the Trimpot)
- a small, flat-head screwdriver
- wiring tables document
Assemble the parts:
This process step is described in the following two videos:
Wiring the Proximity Sensors
What you need:
- (2) 4-wire groups of “clamped and glued” jumper wires
- (2) RJ11 female jacks
- (8) crimp-on wire connectors
- a scissors
- a pliers
- a ruler
Assemble the parts:
In this step, the two sets of 4-wire groups are connected to the 2 sets of 4 wires attached to each of the RJ11 phone cord jacks. Each wire in each 4-wire set is joined together using a crimp-on wire connector.
Before joining the wires, the extra length of the RJ11 jack and jumper wires is removed to make the later insertion of the wiring into the enclosure easier.
The wiring tables are used to record the color of the jumper wire that should be attached to each of the RJ11 jack wires.
Refer to the video for a description of how to fill in the wiring tables and how to properly use the crimp-on wire connectors.
This process step is described in the following video:
Wiring the Buzzers
What you need:
- (2) 2-wire groups of “clamped and glued” jumper wires
- (2) RJ11 female jacks
- (4) crimp-on wire connectors
- a scissors
- a pliers
- a ruler
Assemble the parts:
In this step, the two sets of 2-wire groups are connected to the 2 wires attached to each of the RJ11 phone cord jacks (after the black and yellow wires have been cut away). Each wire in each 2-wire set is joined together using a crimp-on wire connector.
Before joining the wires, the extra length of the RJ11 jack and jumper wires is removed to make the later insertion of the wiring into the enclosure easier.
The wiring tables are used to record the color of the jumper wire that should be attached to each of the RJ11 jack wires. Note that some buzzers are more sensitive than others regarding which of the buzzer pins is connected to power and which is connected to ground. The buzzers specified in the parts list don’t make a distinction.
Refer to the video for a description of how to fill in the wiring tables and how to properly use the crimp-on wire connectors.
This process step is described in the following video:
Insert Buzzers and Proximity Sensors into their Enclosures
What you need:
- (2) buzzer and (2) proximity sensor wiring harnesses
- (2) sets of 3D-printed buzzer enclosures
- (2) sets of “mirrored,” 3D-printed proximity sensor enclosures
- (6) #4 – 3/8″ screws
- a small Phillips-head screwdriver
Assemble the parts:
Proximity Sensors:
Insert the cylindrical parts of each proximity sensor into the matching hollow cylinders of the enclosure. Next, slide the connected RJ11 phone cord jack into the matching opening in the enclosure (the flat side of the jack goes in first). Push the connecting wires into the empty space of the enclosure half while sliding the other half of the enclosure into place.
Use the pointed end of a small Phillips screwdriver to clear out the thin plastic filaments that cover the hole in the back of the enclosure:
Now, insert two screws to hold the enclosure together.
Repeat these steps to assemble the second proximity sensor harness and enclosure.
Buzzers:
Choose the enclosure half without the long center post. Rest the buzzer on the half-cylinder carve-out and insert the flat side of the RJ11 jack into its slot. Work the post of the other half of the enclosure around the wiring. Don’t try too hard. You just don’t want to pinch the wiring with the post. There will be plenty of space for the wiring in the space between the two halves. Use a single screw to temporarily join the enclosure halves.
Repeat these steps to assemble the second buzzer harness and enclosure.
This process step is described in the following video:
Testing All Components and Wiring
What you need:
- the Raspberry Pi Pico and connected components from the previous step
- (4) telephone chords
- USB data cable with micro USB plug
- the computer with a USB port on which you installed Thonny
- a copy of the “assembly test.py” program
- a hard, free-standing object that you can place between the proximity sensors
Assemble the parts:
You will launch Thonny and load the “assembly test” Python program. The program will present you with a menu of tests. Each test will validate one type of component in your assembly.
Each test runs independently of the other tests, and you can run each one as often as you’d like while you troubleshoot your work to this point.
This process step is described in the following video:
Mounting the Pico to the Front Half of the Control Unit Enclosure
What you need:
- The Raspberry Pi Pico and the parts connected to it
- The front, 3D-printed half of the control unit enclosure
- (4) #4 – 3/8″ screws
- a small Phillips-head screwdriver
Assemble the parts:
Disconnect the four phone cords from the four RJ11 jacks connected to the screw terminal break-out board. You can disconnect them from the proximity sensor and buzzer enclosures as well. You won’t be reconnecting them until you’ve finished mounting all components on the walker or gait trainer.
Wrap the RJ11 jack wires around the underside of the screw-terminals breakout board and route them between the two attachment pedestals on each side of the enclosure. Left-side component wires to the left and right-side component wires to the right.
Place the RJ11 jacks into their respective slots with the buzzer jack (2 wires) above the proximity sensor jack (4 wires).
Place the breakout board on the four pedestals, ensuring that you’ve captured all the wires between the pedestals and haven’t pinched a wire.
Screw the board to the pedestals.
Now place the potentiometer in its slot on the right side of the enclosure. The 3-wire clip should sit parallel to the front of the enclosure. It doesn’t matter whether the wires are facing up or down.
This process step is described in the following video:
Mounting the Battery Pack to the Back Half of the Control Unit Enclosure
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What you need:
- The battery pack and batteries
- The back, 3D-printed half of the control unit enclosure
- 4″-long micro-USB to USB A cable
- Optional: magnetic micro-USB plug
- (4) #4 – 3/8″ screws
- a small Phillips-head screwdriver
Assemble the parts:
Disconnect the phone cords and proximity sensors from the other components.
Insert the two RJ11 phone cord jacks of the Pico assembly into the openings in the thinner, Pico-side….
This process step is described in the following video:
Putting the Two Halves of the Control Unit Together
What you need:
- The Raspberry Pi Pico and the components directly connected to it
- the two 3D-printed enclosure halves of the control unit
- battery holder with two rechargeable batteries installed
- short, flat USB to micro USB cable
- (12) screws
- a Phillips-head screwdriver
Assemble the parts:
Disconnect the phone cords and proximity sensors from the other components.
Insert the two RJ11 phone cord jacks of the Pico assembly into the openings in the thinner, Pico-side of the enclosure (flat side inserted first).
Wrap the wires coming from the two jacks around the long side of the terminal breakout board as you place it onto the four screw pedestals. Screw the terminal breakout board to the enclosure.
Lay the potentiometer and buzzers into their respective holders—a bit of adhesive may make this easier, but it’s not absolutely necessary.
Insert the small, flat USB cable into the battery holder. If you’ll be using one, this would also be a good time to insert the magnetic USB connector into the battery holder.
Use four screws to attach the battery holder to the four pedestals in the thicker battery side of the enclosure.
Put the two enclosure halves next to each other. Tip the Pico half, twist the free end of the USB cable, and insert it into the Pico’s USB port. Now flip the battery half over the Pico half and work it into place, moving the potentiometer and buzzers back into their receptacles as necessary.
Use four screws to attach the two enclosure halves.
This process step is described in the following video:
Operating the Control Unit
Attaching Clips to the Proximity Sensor Enclosures
What you need:
- the (2) assembled proximity sensor enclosures
- (2) appropriately sized and angled clips
- (4) #4 – 3/8″ screws
- a small Phillips-head screwdriver
Assemble the parts:
For each assembled sensor enclosure, use two screws to attach the clip to the enclosure through the two open arcs at the ends of the clip base. Don’t tighten the screws down all the way until you’ve attached the sensors to the walker or gait trainer and are satisfied with the positioning of the sensor.
This process step is described in the following video:
Attaching Clips to the Buzzer Enclosures
What you need:
- the (2) assembled buzzer enclosures
- (2) appropriately sized and angled clips
- a small Phillips-head screwdriver
Assemble the parts:
You’ll use the same screw that you used when inserting the buzzers and wire harnesses into the enclosures to attach the clips.
Remove the screw from the enclosure, holding both halves together, and attach the clip to the enclosure using the center hole on the clip.
This process step is described in the following video:
Final Assembly of the Proximity Sensor System
What you need:
- the assembled control unit,
- the two assembled proximity sensor enclosures,
- the two assembled proximity sensor enclosures,
- the four RJ11 phone cords,
- an appropriate set of 3D-printed mounting clips if not already attached to the components,
- an appropriate collection of Velcro straps for mounting the control unit and managing the phone cords.
Assemble the parts:
This process step is described in the following video: