Electronic Product Design Progress Report: Week 6 (Midterm Report)

Fully Working Breadboard Prototype

After discovering that the MCP23017 has built-in pull-up resistors and updating libraries, I built a functional prototype on a breadboard:

PCB Version 2 Woes

After redesigning the circuit and sending the circuit board design to OSHPark, the boards arrived within a week. I then solder the boards only to discover a problem: the MCP23017 chip only lasts a minute then stops working. Having seen this problem before, I suspected that the chip is super sensitive to temperatures and therefore is very difficult to hand-solder.

Version 2 of the PCB. Note the melted hole in the table on the right. This comes from using removing TSSOP packages using hot air.

Version 2 of the PCB. Note the melted hole in the table on the right. This comes from using removing TSSOP packages using hot air.

After removing the chip from the board using a hot air gun, I tried soldering another chip to the board. This one was dead on arrival. I repeated this process a couple of times and even melted a couple of buttons, a power switch, and the work table.

While the boards are designed well this time, the chips are allergic to hand soldering. Therefore, I am re-evaluating the use of the chip in the design and may make another PCB that uses a DIP package instead. Initially, I chose this chip to save space in a portable device but the chip is proving to be too difficult for the prototyping stage.

3D Printing Success Story

After designing a case for the portaMid that would not fit on any cheaply available 3D printer, I really wanted to remake the case so I could try (and possibly fail) a 3D print. While waiting on the version 2 portaMid PCBs, I realized that I needed to make a custom case for another project I am working on for my thesis.

This project utilizes an accelerator and vibration motors to create an input device that can give vibrotactile feedback to the user. I wanted to make the device so that it may be strapped onto the user’s arm near their wrist using a standard NATO-style watch band.

After some work in Fusion 360, I printed the design using PLA with PVA as the support material. The design features screw holes for a Feather board, a hole for the USB charging port, a hole for the on/off switch, and a lid that snaps into place using tabs. I found the snap design on the Adafruit YouTube channel and thought it was the best design as it used no screws and could easily be removed.

The part printed well and all components fit in place nicely!

Plans for the Remaining Weeks

Since I am still having difficulties using the TSSOP chip, I may look into having the chip placed on the board by a professional or redesign the board so that it accepts a DIP package version of the MCP23017. This will also give me the opportunity to shrink the board horizontally a tiny bit and add an extra hole in the middle for more support. This could be accomplished by next week.

The case will be designed and laser cut, with buttons 3D-printed, by week 7 or 8. I am considering dropping the support for a phone case so that the product may be designed a little faster. I hope to make two of the products so that I can send one out for testing by week 8 or 9. After that, I will test and make refinements to the software, as per the feedback given by the testers.