MAQS Boards Assembly & Test

The questions below are due on Friday December 31, 9999; 11:59:59 PM.
 
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Assembly and test of your two MAQS boards will occur over two weeks, and so due after spring break. You'll need to do the board assembly in EDS where you have access to the soldering tools.

Although all the assembly and testing are due after spring break, you are welcome to do it earlier.

Sensor board assembly and test

Instructions are in lab06.

Power board assembly

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

Get your boards and parts

Your boards are located in the tall box in Locker 5 in EDS.

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 made 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 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

If you realize that your micro USB connector is located either in the wrong direction or in the middle of the board, making it hard to access, you can use the vertical micro USB connectors we ordered! In this case, you would want to attach the micro USB connector separately for ease.

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

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 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 sensor. That part was 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.

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 & person(aka,Power_Joel_pic1.jpg, Power_Joel_pic2.jpg, ...).

Insert the URL below:

Assembly pics URL:

Testing the Power board

Test 1: Some checks before powering up

The power board is less tolerant of wiring mistakes than other boards. So our first test will be to make sure there is no short between power and ground. Use a multimeter to check the resistance between 5V power pin on the MCP73871 and ground pins -- hopefully you have test points that make this easy to check.

Test 2: Check USB power functionality

One use case of the power board is that when it is connected to USB input (5V), the MCP73871 chip sends that 5V to the AP7361C regulator, and the regulator outputs 3.3V.

Connect your power board to USB power. Check voltages on certain pins/traces:

  • MCP73871 pin 18/19 (IN) should be ~5 V
  • MCP73871 pin 1/20 (OUT) should be ~5 V
  • AP7361C pin 5 (OUT) should be 3.3 V
  • The power status LED (if you have one) should turn on

Test 3: Delivering power

Next, we will want to see whether the power board can power an ESP32C3.

First, download code on your ESP32C3 board that will connect to WiFi and post to your flask server. We do this because we want to stress test the power board, and the highest peak power draw occurs when the ESP32 is posting to WiFi. Start by powering the ESP32C3 board from USB or the Adafruit MCP73871 breakout board to make sure that code is working and posting.

Next, connect the ESP32C3 board from the 3.3V and GND pins on your power board.

Make sure the MCU power status LED lights up, and then check to ensure that you are logging data to the server. If so, you are delivering power!

Test 4: Charge the battery

The next functionality of the power board is that it should be able to charge a LiPo battery.

Disconnect your power board from the ESP32C3 board.

Connect the power board to USB, attach the battery. Check your status LEDs. The PG LED should light up, as should the STAT1 LED (see Table 5-1 in the MCP718731 datasheet).

Come back after 2 hours. Once the battery stops charging, the status LEDs should change. Check Table 5-1 to see what they should be, and make sure you observe that!

Test 5: Run off battery

The final functionality is that the power board should be able to run the rest of the system from battery power alone.

With the battery charged, disconnect the battery. Connect up your ESB32C3 board. Reconnect the battery. If everything works well, you should be posting to the server off battery power!

Power board testing video URL: