Author: lmoiseye

This week mostly had me tied up by a pretty tight crunch at work, but I still got through most of the goals set out for this week. These were mainly to get the demo hardware working as well as finalizing the BLE module trade study and selection. I also worked with MeeDm and Tarush on the Design Proposal presentation.

One of the most unexpected hurdles in choosing the BLE module ended up being totally unrelated to technical trade-offs: logistics. As it turns out, the world is experiencing a really bad semiconductor shortage, and the supply chain for ic’s and mcu’s has been left in a rough state as a result. Almost all the options I considered ended up having to be scrapped due to either a development board or module not being available – in some case’s the ic itself was out of stock with lead times ranging from 18-52 weeks!

In the end I settled on the DA14531 BLE module. The primary points I considered were power consumption, ease of development/implementation, and supply chain; the DA14531 knocked each category out of the park. This IC features an ARM Cortex-M0+ processor and achieves absolutely top-of-the-line power consumption specs of under 22µA/MHz clock rate and 240nA hibernation mode. Dialog Semiconductor provides ample documentation and has an active forum – critical to ease of development. Finally, the IC and its accompanying evaluation boards are in stock and readily available from a number of distributors, including DigiKey. With the order placed, my focus will now shift towards getting the prototypical schematic and layout finished for the BLE tags.

Speaking of tags, I also worked on the Arduino-based demo hardware and completed assembly of the RFID bluetooth tag:

The tag features a coin cell holder, headers for an HC-05 Bluetooth module and RC-522 RFID reader, and power switch. It’s quick, it’s dirty, and it works. Along with the load cell based weight sensing tag, this RFID tag will allow the team to develop and test the full project pipeline on real hardware without waiting for the actual BLE tag pcb’s to be spun up. Next week I’ll wrap up the demo hardware by putting it in a nice, custom-made enclosure. I’ll work with MeeDm to get it connected to the RPI and I’ll work with Tarush to have the web-app display communications between the demo hardware and the RPI hub.

As I learned the hard way this week, a new risk to consider is time commitment at my job. Going forward I’ll have to actively temper my responsibilities there with my work here.

 

This week was a little slower on development than past weeks, but we still all chugged along.

I presented our Project Proposal on Monday and, along with everyone else, filled out feedback forms on the Monday and Wednesday presentations. It’s so exciting to see all the interesting projects the capstone teams are working on this semester!

Here’s the raw presentation (it’s a little quiet so check your volume):

I mainly focused on re-printing some of Shelley’s (our robocat test dummy smarty) parts. The main issue we ran into was that the original parts we printed suffered from “elephant’s foot” – basically the first layer was pressed down too much by the extruder head and expanded out too far to be within part tolerances. I recalibrated my printer and (after a terrible failure) got the fresh parts done around Friday.

I had to leave for Delaware on Friday morning, so Shelley will have to wait until this upcoming Monday to be fully assembled.

Before leaving, I also worked on putting together the demo parts – mainly soldering the HX711 breakout, arduino nano, power switch, coin cell holder, and other similar components. I also grabbed some cords from Roboclub and got the our Raspberry Pi set up with raspbian, net reg, and a static ip address.

Next week will see Shelley up and running (literally), the demo working, and apache web server hosting a basic “hello world” web app built in django. I’ll also wrap up the trade study on BLE modules, select one, and begin work on the schematic for the prototypical Tag pcb.

…i’ll also have to clean up our bench space…

 

 

 

 

 

Hello World!

The main team goals for this week were to finalize technical requirements and write up course documentation (gantt chart schedule, proposal slide deck, website, etc.). I mainly worked on the solution approach, preliminary system diagrams, and technical requirements.

 I also researched BLE modules, RFID parts, and weight sensors, and worked with MeeDm to conduct a trade study of using BLE versus WiFi. We ultimately settled on the BLE standard because of its superior power consumption and reduced implementation complexity. I researched the benefits and trade-offs of sensing weight via load cells versus force sensitive resistors – for our use case, the much higher accuracy and granularity achievable with load cells makes them the clear choice.

Throughout the week, I scrounged up free parts from the Robotics Club and Ideate Physical Computing Lab in order to spearhead getting a demo of our system running as fast as possible. I got basic RFID and weight sensing working with Arduino Unos and Nanos and will have Bluetooth ready early this upcoming week. I designed a simple load cell mount in Solidworks and 3D printed it, and will work on getting the whole demo together into a clean package this upcoming week.

Finally, our testing strategy initially assumed we would purchase a couple stuffed cats and implant them with RFID microchips. Instead, I ended up stumbling on Petoi, a company founded by some CMU grads. They made a project called OpenCat, an open source, Arduino based robot cat. Of course I had to print it out, and I found all the necessary parts (microcontroller, ultrasonic sensor, hobby servos, motor driver, and rf receiver) in RoboClub! Next week will see this pile of “managed chaos” transformed into our test cat, Shelley.