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Interactive Circuit Board

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Habibur Rahman edited this page Sep 27, 2020 · 9 revisions

Interaction Circuit Board

The interaction circuit board is an extension of the bela consisting of an electret microphone, an accelerometer, IR proximity, and RGB LED and a strip LED driver.

The circuit board has two segments that are bridged with connecting wires. The PCB design has both the segments fabricated together connected by drill-bits that can be separated by breaking the board. Once the board is broken, the edge of the boards can be smoothed by filing.

Layout Desing

  1. The interconnection of the system can be accommodated over the printed circuit board of two-layers only without the need for intermediary layers for power and ground.
  2. The one-half segment of the board accommodates the electret microphone with an adjustable gain amplifier, and accelerometer and RGB LED and pin-row for connecting the IR-proximity sensor
  3. The second half segment of the board stacks on top of the bela and also accommodates the darlington array for driving strip led.
  4. The two segments are bridged by connecting wires. The layout design may complain about unconnected tracks between the boards for ground (GND), 5V power supply and 3.3V power supply. However, the bridge cable will ensure the connection of these between the two segments of the board

Exporting the gerber files

The Gerber files can be generated in KiCAD.

  1. Open the PCB layout
  2. Click on File > Plot
  3. A window opens up prompting the layers to be plotted and the output directory. Choose the output directory where the gerber and drill files are to be generated. Select the included layers. The required layers are F.Cu, B.Cu, F.SilkS, B.SilkS, F.Mask, B.Mask, Edge.Cuts. Click on Plot. Also generate the drill files by clicking on the ‘Generate Drill Files’ button.

Placing the order for the PCB

  1. Several PCB manufacturing companies offer low-cost fabrication of the PCB design, such as JLCPCB and PCBWay
  2. Each manufacturer requires you to upload your design files (Gerber and Drill file), which then undergoes a reviewing process to estimate the final manufacturing cost and also notify you of possible errors in the design file.
  3. Depending on the manufacturer, the design may be considered as 2 separate designs you can be quoted a slightly higher price.
  4. JLCPCB allows you to upload the gerber files and automatically determine the parameters such as the number of layers, and the dimension of the board.

  1. The remaining parameters can be adjusted manually, such as the thickness of the copper, the color of the solder mask, etc.
  2. A stencil can be ordered that allow spreading the solder pasted evenly over the exposed copper areas where the c

Bill of Materials

Populating the board

  1. Clean the unpopulated PCB with alcohol
  2. Place the PCB over a clean surface with the SMD soldering sides facing up. Tape the PCB to a clean surface.
  3. Place the stencil over the PCB and align the slits of the stencil to the pads of the PCB.
  4. Drop a little bit of solder paste over the stencil. Use a squeegee to drag the solder paste over the slits.
  5. Gently remove the stencil and inspect the solder paste over the pads. If the solder paste is smudged or placed outside the pad, clean both the PCB and stencil with alcohol and repeat the process until the solder paste lays perfectly over the PCB pads.
  6. Place the SMD components on the PCB gently making sure the paste is not smudged.
  7. The reflow oven usually has 2 phase heating process.

Below is the reflow profile for the ChipQuick SMD291SNL50T3. We can infer that the Phase 1 temperature and time are 175-degree Celsius for 90 seconds respectively and phase 2. temperature and time are 249 degrees Celsius for 60 seconds. These profiles can be set in the reflow oven. If you are using a different solder paste, look into the manufacturer's datasheet to find the reflow profiles.

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