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  • Exercises 06
  • MCU & Power Boards Assembly

    • MCU & Power Boards Assembly

    The questions below are due on Thursday March 23, 2023; 10:00:00 AM.
     
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    Board assembly and test will occur over two psets (EX06 and EX07). The first part (assembly) is due in EX06, and the second part in EX07 (though we aim to release the testing early in case you want to do it early). You'll need to do the board assembly in EDS where you have access to the soldering tools.

    These exercises will be completed as a team. The main tasks are to

    • Assemble and test the MCU boards
    • Assemble and test the power management boards

    Due for Ex06:

    • Your team should assemble N power boards
    • Your team should assemble N MCU boards

    Due for Ex07:

    • Your team should test N power boards
    • Your team should test N MCU boards

    Where N is the number of people on your team so that everyone will have a working mcu/powerboard combo.

    The testing is due with EX07 after spring break, though you are welcome (and encouraged!) to do it earlier.

    Board assembly

    You all have some experience now with board assembly. The MCU and power boards are similar to the sensor board, so the steps are similar.

    It takes a village

    Half the team designed MCU board, and half designed the power board. But we want each team member to have a fully functioning system when you're finished. So...you'll need to decide how to apportion the work:

    • Each person could assemble/test one MCU and one power board
    • The MCU people could assemble/test all the MCU boards, and the power people could do all the power boards.
    • Some other combination. You decide!

    Since it's possible that not all designs will work, you should consider assembling and testing one board of each design first, before assembling & testing additional boards, just in case there is an issue with the design. Or not.

    Get your boards and parts

    Your boards are near Joe's office on top of a cart.

    Paste!

    Same as before, paste all the SMT pads on your boards. Solder paste can be found in the minifridge in the back corner of the stock room.

    The most prevalent failure mode during sensor board assembly was too much paste. A little goes a long way!

    Also please remember to wear gloves when handling solder paste!

    Get components

    Get resistors, capacitors, LEDs same as you did for the sensor board. Same with USB micro connector.

    • The ESP32-C3-WROOM ICs are pretty big and easy to handle. Get one for each MCU board.

    • The MCP73871 power management chip is a pretty small QFN part. Grab one, don't lose it!

    • The AP7361C LDO is even tinier...

    • A micro USB connector

    You can hold off on grabbing the rest of the components:

    • JST connectors -- 2.5mm ones for MCU board and power board. A 2.0mm one for the battery connector on power board

    • Push buttons for MCU board

    • Battery and pouch

    Give it some air

    Same as for sensor board, hit the board with some hot air. Then inspect. Look to make sure all the pins on the ESP32, MCP73871, and AP7361C are distinct. If adjacent pins are connected, use the tiny wick and a solder iron to suck up excess solder. Ask for help if needed!

    The MCP73871 is a bit more complicated to solder than the SHTC3/SGP41 sensors. Those parts were DFN (dual, as in pins on two sides). This part is QFN (quad, as in pins on all four sides). But we are ready for the challenge!

    Solder the thru-hole components

    Next, collect the thru-hole components and solder them using the iron. All components should be on the top side of the board, making assembly easier.

    And same as last board, you can either solder in the test points or just leave them as vias to probe later.

    If you are soldering buttons, they have an orientation, as shown in the datasheet. They should fit one way, but not if you rotate them 90 degrees.

    The USB micro connectors have metal tabs that fit into oval slots on the board. You will want to solder those tabs to the metal on those slots, to provide extra mechanical strength.

    Once you have your boards assembled, take pictures of them and place in your team's google drive folder. The pictures should be detailed enough that we can determine visually if the boards appear properly assembled. So this will need more than one image/board. So please name your image files so that is is clear which images corresponds to which board, and so that we can tell that there is one board of each type per team member (aka, MCU_Joel_1.jpg, MCU_Joel_pic2.jpg, ..., Power_Joel_pic1.jpg, Power_Joel_pic2.jpg, ...).

    Remember, there should be images of 1 MCU board and 1 power board per team member on the site.

    Insert the URL below:

    Assembly pics URL:

    The assembly is due with EX06. The testing is due with EX07 (after spring break), though you are welcome to do it earlier.