Week 18 - Project development¶
What tasks have been completed, and what tasks remain?¶
Completed¶
- Conceptual design
- Preliminary testing
- Enclosure design
Not completed¶
- Finalize design
- Field testing
- Final PCB milling and stuffing
- 3D-printing enclosure
- Packaging and assembly
What has worked, what hasn’t?¶
nRF24L01 vs HC-10¶
What worked was communication via the HC-10 433mhz module. It was easy to set up communication via this board compared to using the nRF24L01. It can simply be treated as a serial connection. The downside is that there is no protocol ensuring data transmission and integrity. On the other side the data transmission rate is higher. On the boards I made I was unable to connect to the nRF24L01 module, and I was not eventually able to find out the reason.
Library sizes¶
Additionally, a problem that I’ve run into is the size of the SAMD11C. To communicate with the VL53L1X time-of-flight distance sensor a library is required, which is essentially a wrapper around the I2C library, and that library exceeds the flash memory of the SAMD11C. Additionally, the library for the nRF24L01 is quite large and uses most of the storage space for the SAMD11C.
VL53L1X vs SR-04¶
From my tests the VL53L1X seemed to give more stable measurements (fewer outliers) as well as performed more robustly. However, it is more expensive and requires a library to operate. The SR-04 was less reliable and robust, but cheaper and does not require a library.
SAMD21E vs SAMD11C (vs ATTiny)¶
I attempted to scale up to a SAMD21E in order to address the above-mentioned size concerns. However, I was unable to program the board I had made and had to revert back to an older version due to time management concerns. Most of the other students from my year chose ATTiny-based designs, which are more robust as well as operate at 5V. In my case that would have been easier as well, because the modules I’ve need 5V as well. However, I am able to debug via USB without adapter boards and a serial interface in between, so that is also valuable.
What questions need to be resolved?¶
Is the downward angle of the case sufficient to aim the device backwards?
What is the issue that is causing me not to be able to load sketches onto the SAMD21E?
What will happen when?¶
In the final weeks I will have to complete the tasks that are not yet completed. Mostly 3D-printing and designing at home in the evenings and working on electronics during the day in the lab.
What have you learned?¶
I have noticed that designing new PCBs, as well as determining which components I need, is going a lot faster than earlier.