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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.
  1. The gerber and drill files should be available in the selected directory. Compress the folder to a zip file.

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. Click on ‘Add your gerber file’ and add the zip file created. The parameters for layers and dimensions should be automatically filled. Choose the PCB quantity that needs to be ordered. Since the board design has two segments, the PCB manufacturing company usually considers the design to consist of 2 separate design which may also be charged extra. Most of the other settings can be kept at default, such as the PCB Thickness being 1.6 and the PCB Material Type being FR4-StandardTg 130-140C. Order a stencil if needed by checking the ‘Order together with PCB’.
  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

Part No Description
150505m173300 RGB LED
ERA­6VEB1000V RES , 100R, 0.1%, 0.125W, 0805, THIN FILM
TC33X­2­103E Trimpot , Single Turn, Cermet, Top Adjust, 10 kohm, Surface Mount, 1 Turns
CMA­4544PF­W ---
MAX4466EXK+T Microphone Preamplifier , 200kHz Gain Bandwidth, 2.4 V to 5.5 V supply, SC-70-5
BLM21SP601SN1D Ferrite Bead , 0805 [2012 Metric], 600 ohm, 2.3 A, BLM21_SN Series, 0.06 ohm, ± 25%
C0805X104J1RACTU SMD Multilayer Ceramic Capacitor , 0.1 µF, 100 V, 0805 [2012 Metric], ± 5%, X7R, X Series FT-CAP
C0805X103J5RACTU SMD Multilayer Ceramic Capacitor , 10000 pF, 50 V, 0805 [2012 Metric], ± 5%, X7R, X Series FT-CAP
C0805X106K8RACAUTO SMD Multilayer Ceramic Capacitor , FT-CAP, 10 ,F, 10 V, 0805 [2012 Metric], ± 10%, X7R
C0805X101F8HACAUTO ---
ERA­6VEB1001V RES , 1K, 0.1%, 0.125W, 0805, THIN FILM
ERJ­6RED1004V SMD Chip Resistor , 1 Mohm, ± 0.5%, 100 mW, 0805 [2012 Metric], Thick Film, Precision
ERA­6VEB2202V RES , 22K, 0.1%, 0.125W, 0805, THIN FILM
ADXL337BCPZ­RL7 MEMS Accelerometer , Analogue, X, Y, Z, ± 3g, 1.8 V, 3.6 V, LFCSP
10129382­912003BLF BTB CONN , HEADER, 12POS, 2ROW, 2.54MM
M20­9771046 ---
TOL­12878 ---
BA12003DF­ZE2 ---

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.
  1. Place the entire PCB in the reflow oven. 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.
  2. Once the reflow is completed, let the board cooldown. The SMD parts should now be soldered onto the board.
  3. Inspect under the microscope for any solder bridge or tombstoning. Solder bridges are usually formed between adjacent pins of an IC can be removed by using a solder wick.

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