Split-flap build guide

Fastener assignments are from the upstream screw table. Per unit: 2 of each unit fastener. The case needs the same count for every size.

Tools

What each printed part looks like

Upstream's renders of the 10-unit parts. Shorter cases have shorter Left and/or Right pieces.

Both views have the board's top edge up: that's the edge nearest U10 and the U4 chip, and U7 and U8 sit on the opposite edge. The numbers on the maps are the soldering order in the table. The board says Version 1.2 on the top side; the photos in stage 3 show an older version.

1. U4, ULN2003A, bottom side. Place it so the dot on the chip is at the top left, as in the bottom view. Add flux, tack one corner pin, check that every pin sits on its pad, then solder the rest. Clear any bridges between pins.
2. C2 100 nF and C1 330 nF, bottom side. They go in the white box marked 5V, C2 above C1. Do not use the C5 spot just above them. These capacitors have no polarity.
3. SW1 and the Nano headers, top side. Fit the DIP switch with its ON edge toward U6 and switch 1 on the left. Then fit the two 1×15 female headers into the long rows. Plug the Nano in, USB end toward the top edge, to hold them straight while you solder them from the bottom side. Unplug it afterwards.
4. JST-XH sockets, top side. U10 (5-pin), U6 (3-pin), then U7 and U8 (4-pin). U10, U7 and U8 each have a peg that fits only one way. U6 has none, so match it to U10 next to it. Hold each socket flat against the board while you solder it.
5. U3, L7805, top side. Stand it upright with the metal tab toward the Nano and the printed black face toward U7 and U8. Left to right, the legs are IN, GND, OUT. Backwards, it puts 12 V on the 5 V rail and destroys the Nano.
   Don't lay it flat, even though the older boards in the stage 3 photos have it that way: its metal tab would rest on the empty ESP-01 pads.
6. Meter check, no power, no Nano. Use continuity mode on the socket pins from the bottom side. GND and 12V on U8 must not beep, and neither must U6's two outer pins. U8's GND pin must beep to U6's middle pin. The pinouts are in the table below.
7. Make the power lead. Plug the 200 mm XH-4 cable into U8. The labels beside U8 name its pins, left to right: 12V, GND, SDA, SCL. Tag each wire at the socket, because cable colours mean nothing. Unplug it, solder 12V to the DC jack's centre pin and GND to its outer contact, and tape over the SDA and SCL ends separately so they can't touch anything.
   Check with the meter which jack tab is the centre pin, and that your supply is centre-positive.
8. First power, no Nano. Plug the lead into U8 and apply 12 V. The Nano header's 5V hole, 4th from the bottom of the left row, should read 4.9–5.1 V against GND. If it doesn't, or the 7805 gets hot, disconnect and recheck it.

FlapDrumOuter is the long open cylinder. FlapDrumInner is the disc with spokes, four large holes and the motor hub. Each has a ring of 45 flap holes, and the flaps hang between the two rings.

The two drum halves are the CAD parts. The magnet and flaps are simplified shapes. Yellow marks the parts a step moves, orange what it adds.

1. Stand FlapDrumOuter on its flange with the plain end up. Inside, two round bosses stand against the wall, about 10 mm below the rim. Melt an M2 insert into the top of each one with the soldering iron at about 200 °C. Push straight down and stop when it is flush.
   2× M2 insert3D

   

2. Solder a 300 mm XH-3 cable to each KY-003, by function and not by position, because the two ends use different pin orders. Plug the cable into a U6 socket to see which wire is which, then connect the wire at U6's 5V pin (nearest U10) to the sensor's +, the middle wire to −, and the wire nearest SW1 to S.
   On most KY-003 boards the middle pin is +, so a straight-through cable would reverse the power. Go by the labels on your board. If only S and − are marked, the unmarked pin is +.
3. Find the magnet's pole. Plug the sensor into U6 of the tested board and apply 12 V to the board. Hold the magnet to the sensor: when its LED lights, that face points at the sensor. Mark that face with a marker. If the LED stays dark on both faces, disconnect and recheck the wiring.
4. On FlapDrumInner, find the small 2 mm pocket on the hub side (the side the hub sticks out of), 20 mm from the centre. Glue the 2×1 mm magnet into it, marked face out. Let it cure.
   3D
5. Push FlapDrumInner into the plain end of FlapDrumOuter, hub first. Its two small counterbored holes must land over the inserts. It's a friction fit: it takes some force, and the halves can still be pulled apart.
   3D
6. Each flap ring has a tiny round mark next to one hole (arrow in the photo). The screw holes line up in two positions. Use the one where the two marks also line up.
   3D

   

7. Lift the outer half a little, slide in a few flaps, press it back, and repeat. Start at the mark with Flap 2, the flap that is blank on one side and has part of an A on the other. Continue 3, 4 … 45, then Flap 1 last. After the first dozen, flip through them by hand: the halves should meet to form A, B, C. If they don't, take them out and reverse the direction around the drum or the way the flaps face.
   3D
   Flaps go in by file number, so keep the plates separate. If you printed the five Flaps PT plates, they are the whole set. If you printed upstream's flaps, take 1, 14, 15, 24, 25, 28–31 and 41–45 from Flaps PT instead. The drum then reads: blank A–Z Ã Ç É 0–9 Á . TikTok Instagram Facebook.
8. Lock the halves: two M2×8 screws through the counterbored holes in FlapDrumInner into the inserts.
   2× M2×83D
9. Spin the drum by hand. Every flap should drop cleanly and none should snag.

UnitFrame has a flat base, a side wall for the motor, and an upright PCB plate at one end. The PCB goes on the outside of that plate. Later the plate is screwed to the middle frame and the PCB pokes through a window.

The frame and drum are the CAD parts. The motor, sensor and board are simplified shapes placed on the frame's real mounting holes. The flaps and cables are left out.

1. On the drum side of the PCB plate, each of the four corner bosses has a hex pocket. Push M3 nuts into two diagonally opposite pockets: top left and bottom right, for example. If a nut won't seat, put an M3 screw through from the PCB side and tighten it to pull the nut in, then take the screw out.
   2× M3 nut3D
2. Set the stepper against its two posts on the side wall, shaft pointing away from the wall, and fix it with two M4×8 screws through its mounting ears. Its wires exit toward the small round post at the far end of the base, as in the photo.
   2× M4×83D
3. Screw the KY-003, with its cable already soldered, to its mount with two M2×4 screws, as in the photo.
   2× M2×43D

   

4. Route the stepper and sensor cables through the back of the frame and press them into the cable channel.

   

5. Fix the PCB to the outside of the PCB plate. It fits either way up, so check first: U10 and U6 go toward the hall sensor end, and U7 and U8 toward the small round post. Drive two M3×6 screws through opposite corners into the 3 mm post holes. They cut their own thread, so stop when snug. Plug the motor into U10 ("28BYJ-48 Stepper 12V", 5-pin) and the sensor into U6 ("Magnet Sensor", 3-pin).
   2× M3×63D

   

6. Fit the drum: its open end goes over the motor and sensor, and the hub in FlapDrumInner presses onto the motor shaft. Line up the flat in the hub with the flat on the shaft. Push it on until it is seated, then turn it by hand: it must not rub the frame, and the magnet must pass close to the sensor.
   3D
7. Set the DIP switch for this unit's position (table in stage 7) and label the frame. Plug in the Nano with its USB end toward U10. Backwards, it can be destroyed at power-up. All 30 pins must be in the headers.

On the PC, in a terminal opened in this repo's folder (the one with platformio.ini), with the Nano on USB and the unit on 12 V through the power lead in U8. Stop pio device monitor with Ctrl+C before each upload, because it holds the port.

1. Flash the offset tool: pio run -e offset_tool -t upload, then pio device monitor. Type an offset (start with 100) and press Enter.
   If the upload fails with a sync error, the Nano has the newer bootloader: change board to nanoatmega328new in the unit and offset_tool sections of platformio.ini.
2. Flash the unit firmware with the DIP at 0000: pio run -e unit -t upload. On power-up the drum homes. The blank flap should show.
   If a neighbouring flap shows, repeat step 1 with a larger or smaller offset. About 45 steps is one flap.
3. Check homing both ways: power up with the magnet right at the sensor, then again away from it. Note whether it backs out and turns, or stops immediately. Either is fine if the blank flap ends up showing. The homing code has never been tested on this hardware, so if it doesn't home, see step 4 of the bring-up list in hardware/wiring.md.
4. Optional: enable #define test in the unit firmware. It should show blank, Z, A, U, N, the Instagram logo, 0, 1, 2, 9 in order. Comment the line out again and reflash afterwards.

Drag to turn the model, pinch or scroll to zoom. Click a step again to replay it. Yellow marks the parts a step moves, orange the screws, nuts and inserts it adds.

1. Dry-fit each layer before anything else: lay its Left, Center and Right pieces face down and push the seams together. They should close without force, with the joint holes lined up. Trim or sand any that don't.
   3D
2. Middle frame inserts. Lay the three middle frame pieces back up: the back is the face with the counterbored holes. Find the 8 plain 4 mm holes in the outer rows, above and below windows 1, 3, 6, 9. Melt an M3 insert into each from the back.
   8× M3 insert3D

   

3. Join the middle frame. Put the Center piece between Left and Right so its tabs lie over their ends. Drop an M4 nut into each of the 4 hex pockets, which open toward the windows. Then drive an M4×20 into each joint from the outer top or bottom edge, through the Center tab and into the nut.
   4× M4 nut4× M4×203D
   A bit of tape over a pocket keeps its nut in while you turn the frame over.
4. Fit the units. Hold each unit against the front of the middle frame with its PCB through a window. Its two nuts line up with two of the four holes around that window. Unit 0 (DIP 0000) goes behind the leftmost window, seen from the front, then 1, 2 … to the right.
   3D
5. Screw the units on. From the back, drive an M3×16 socket-head screw through each of the two holes that have a nut behind them and tighten. The other two holes stay empty.
   2× M3×16 per unit3D

   

6. Daisy-chain the units with the 8 double-ended XH-4 cables: U7 of each unit to U8 of the next, starting with U7 of unit 0. Unit 0's U8 stays free for the power lead, and the last unit's U7 stays empty.
   Check each cable before any power, because a reversed one puts 12 V on SCL. Meter between the two units: left leg of the 7805 to left leg of the 7805, Nano A4 to A4, A5 to A5, and GND to GND must all beep.

   

7. Front cover inserts. Stand each front cover piece on its face so the open back edge points up. Each piece has two 4 mm holes in that edge, one in the top wall and one in the bottom wall. Melt an M3 insert into each, 6 in total.
   6× M3 insert3D
8. Join the front cover. It's the same idea as the middle frame, with 4 joints per seam. Drop an M3 nut into each of the 8 hex pockets inside the top and bottom walls of the Left and Right pieces. At each seam there are 2 near the front face and 2 near the back edge. Drive an M3×8 into each from the outer top or bottom edge, through the Center piece.
   8× M3 nut8× M3×83D
9. Put the front cover on. Lay the cover face down. Lower the middle frame onto it, units first, so the frame's front face sits flat on the cover's back edge. The cover's inserts line up with the counterbored holes in the frame's outer rows.
   3D
10. Screw the front cover on from the back: an M3×16 through each of the 6 counterbored outer-row holes (between windows 1–2, 4–5, 8–9, top and bottom) into the cover's inserts.
    6× M3×163D
11. Join the back cover, the same way as the front cover: an M3 nut in each of the 4 hex pockets, and an M3×8 into each from the outer top or bottom edge. Then fit the rocker switch and the DC jack into the two holes in the left end: the switch in the rectangular hole, the jack in the round one. Unsolder the jack from the power lead first if it won't pass through the hole.
    4× M3 nut4× M3×83D
12. Close the back cover only after stage 7 passes. Set it on the back of the middle frame and drive an M3×16 through each of its 8 deep counterbored holes into the middle frame's inserts. The two keyholes in the back are for hanging it on a wall.
    8× M3×163D

Power (power lead in unit 0's U8)
  DC jack + ── switch ──┬── lead 12V
                        ├── buck IN+
                        └── 1000 µF +
  DC jack − ────────────┬── lead GND
                        ├── buck IN−
                        └── 1000 µF − (striped side)

  buck OUT+ ──┬── ESP32 VIN
              └── level shifter HV
  buck OUT− ──┬── ESP32 GND
              └── level shifter GND

Signals
  lead SDA ── shifter HV1    LV1 ── ESP32 GPIO21
  lead SCL ── shifter HV2    LV2 ── ESP32 GPIO22
                             LV  ── ESP32 3V3

1. Set the buck converter to 5.0 V: feed its IN+ and IN− with 12 V, measure OUT+ to OUT−, and turn the trimmer. Nothing else is connected to its output yet.
2. Wire as above with 22 AWG wire for everything carrying 12 V or 5 V. Cut the power lead's 12V wire and put the rocker switch in it. Use the wire tags you made in stage 1, not cable colours, and insulate every joint.
3. Stick the ESP32, buck converter and level shifter inside the left piece of the back cover with double-sided foam tape, clear of the keyhole and the screw bosses. Leave the ESP32's USB port reachable. The wires must let the cover lie open beside the case. The cover is 23 mm deep.
4. Flash the master: pio run -e master -t upload, then pio run -e master -t uploadfs.
5. Serial monitor at 115200: it prints [bus] scan: 1/9 units answered: 0x10=ok … with just unit 0 connected, and the rest MISSING. Type text; it should appear on the flap.
6. Connect it to Wi-Fi: follow First-time setup in README.md. If you built anything other than 9 units, set units = 9 on its Settings page, because the firmware's default is 9.

Addresses come from the DIP switch, read at power-up: 0x10 plus the switch value, with switch 1 as the highest bit. To change one, set it and power the unit off and on again. Reflashing the ESP32 later means taking the back cover off.

1. Connect the units one at a time. After each, run !scan in the serial console (or open the Status page) and check that its address answers.
2. Full load test: show all 8s, then all blanks, then all 8s. Measure the 12 V rail while they flip: it must stay above about 11 V.
3. Close the back cover (stage 5, step 12). Leave it cycling for 24 hours. The Status page should show last reset: power_on, about 24 h of uptime, and no [bus] timeout lines in the log.