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• Assembling the Bendy SAO

  debraansell • 03/15/2025 at 03:07 • 0 comments

  IMPORTANT: Before starting assembly, please review all instructions to
  make sure you understand the correct alignment and orientation of the
  component parts. The arrangement of the pieces is NOT intuitive and must
  be correct for the Bendy SAO to function correctly.

  STEP 1: ASSEMBLE EACH SECTION

  The exact number of components you receive will depend on whether your
  Bendy SAO assembly consists of three or four (or more) sections. There
  are three different types of sections in a Bendy SAO (top, middle, and
  bottom). You can chain as many middle sections as desired together to
  increase the SAO's length.

  Each section consists of a (1) front PCB, (2) back PCB, and
  (3) acrylic buffer layer. The acrylic buffer layer sits between the
  front and back PCBs. In each segment, the front and back PCBs are joined
  by header pins which must be soldered on the OUTSIDE of the PCB assembly
  so that the header pin insulation sits between the front and back PCBs.

  Assemble and solder each section as shown below BEFORE combining the
  sections into the final assembly. If there is protective paper on the
  acrylic, remove it before placing the acrylic between the PCBs. DO NOT
  FORGET TO PLACE THE ACRYLIC BETWEEN THE PCBs BEFORE SOLDERING EACH
  SECTION!

  Bottom Section:

  Middle Section:

  !!! It is essential that the alignment of the front and back PCBs in
  the middle section matches the image below !!!

  Top Section:

  The image below shows where to apply the solder when connecting the
  front and back PCBs in each section. Be sure to solder the front and
  back PCBs in each section together BEFORE connecting the sections
  together in the final assembly.

  Step 2: Combine Sections into the Bendy SAO Assembly

  Use the plastic push rivets to join the soldered sections together into
  the final assembly. When joining two sections together, the spring
  connectors in one section make contact with the ring pads on the
  adjacent section. The acrylic buffer layer maintains the correct
  separation between PCBs so that the spring connectors don't get crushed.

  Unfortunately I don't have photos of this part, but it's easiest to
  start by joining the bottom section to the middle section of the Bendy
  SAO and follow the steps below:

  (1) Hold the two sections together so that the spring contacts on the
      bottom section are facing the ring pads on the middle section.

  (2) Align the holes of both sections together, then take a plastic push
      rivet, and insert it into the hole in the front PCB of the bottom
      section, and press until the tip of the rivet exits the hole in the
      back PCB of the middle section. You will probably hear a slight
      "pop" as the push rivet settles into place.

  (3) If you can't apply enough pressure to fully insert the rivet with
      your fingers, then place the sections, joined by the rivet, onto a
      flat surface, with the rivet head facing the surface. Apply gentle
      pressure to the assembly until the rivet "pops" into place.

  (4) Once inserted, the sections should pivot smoothly around the rivet
      while remaining attached to each other.

  Repeat this process until all sections of the Bendy SAO are joined
  together as shown below:

• Programming the Bendy SAO

  debraansell • 03/15/2025 at 02:56 • 0 comments

  Programming the Bendy SAO

  The bendy SAO contains an ATTiny 3224 which can be programed using any UPDI programmer.

  If you do not have an UPDI programmer, you can make one with an Arduino Nano or Arduino Uno, by following the directions here: https://fabacademy.org/2021/labs/zoi/week8_emb_programming.html

  and flashing the Nano with the jtag2updi firmware found here: https://github.com/ElTangas/jtag2updi Once the UPDI programmer is working, connect it to the SAO connector. The UPDI pin on the ATTiny is attached to GP1 on the SAO connector, while Voltage/Ground connect to the corresponding pins on the programmer/SAO.

  To display blinky light patterns on the ATTiny, install the following code using the UPDI programmer and the Arduino IDE.

  https://github.com/geekmomprojects/BendySAO/tree/main/SuperConEurope2025/programming/strandtest_wheel_for_bendy_sao

  The Arduino settings should match those shown below (use whatever COM port is attached to the UPDI programmer)

  If you encounter difficulties uploading the code, you may need to run “Burn Bootloader” first.

  Sadly, due to some design decisions I made, there isn’t an easy way to get the SAO to interact with the badge. Though it is connected to I2C, I neglected to put pullup resistors on the ATTiny’s SCL/SDA pins, so it isn’t actually possible to communicate with the ATTiny via I2C.

  And, in a failed attempt to be able to use the Raspi Pico as a programmer, GPIO1 and GPIO2 on the SAO connector are connected to an UPDI programming circuit and can’t be (easily) used directly as I/O for the ATTiny 3224.

  So please enjoy the SAO as a decorative, but not interactive art piece to go with the badge. The design process has been a significant learning experience for me. 

• Programming/Assembly of Bendy SAO

  debraansell • 11/03/2024 at 19:30 • 0 comments

  A PDF overview with assembly instructions is in the "files" section of this guide. More detailed instructions to follow shortly.

• Preparing to Assemble the Assembly

  debraansell • 10/23/2024 at 21:40 • 0 comments

  Once the components were attached to the boards, the two layers of boards had to be sandwiched together with the spring contacts pressing against the circular solder pads. 

  A push rivet goes through the corresponding holes in the two layers to align them and allow them to pivot. The push rivet needs to be the correct height to hold the layers against each other firmly so they don't separate, but aren't too close either. A buffer layer sits in the middle of the opposing PCBs so that the spring contacts aren't crushed. The working height of the spring contacts is about 1.8 mm, so I used 1.6mm laser cut acrylic to create a buffer layer in a shape that doesn't overlap the components. In addition, male header pins hold opposing components together, so I needed to find male header pins with an insulation layer no more than 1.6 mm thick. I found these at DIgiKey.

• SMT Assembly

  debraansell • 10/23/2024 at 21:39 • 0 comments

  Prototype boards came back from JLC, The side-emitting LEDs have tiny solder pads, so I ordered stencils along with the boards for the first time. Amazingly, the solder paste stenciling and SMT soldering worked quite well for the first few boards, and I seem to have routed all the connections correctly. I haven't used these specific LEDs before, but I like the way the attached lens diffuses the light.

• Quick and dirty JLC prototype order

  debraansell • 10/12/2024 at 06:12 • 0 comments

  Submitted prototype (and possibly final as I doubt there will be enough time for iteration) designs to JLC PCB for 6 different boards (front base, front middle, front top, back base, back middle, back top) to comprise a bendy assembly. Working under a time crunch, I'm focusing on keeping things as simple as possible, so I added pads to mount a XIAO 2040 (only $3!) on the front base, to easily program patterns on the LEDs in CircuitPython. The image below shows two columns of boards, with front layer on left and back layer on right. Each column contains one base, two middle and one top board.

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