Alaska is on the edge of advancing climate change. Its unique position of having a fairly untouched landscape populated with a variety of coal mine canaries enables a lot of research possibilities. Our friend Monty is an Archaeologist who helps with camps for kids in Native Villages scattered around the state–Culturalalaska.com. He has been building cache sites for the historical preservation of food with these kids and wanted a way of temperature monitoring that he could leave for about 8 months of winter. A food cache in Alaska is designed to prevent Bear entry and can either be buried or secured in a small cabin-like structure on poles. Unfortunately the warming of the climate makes many of these handy refrigerator designs more like a microwave this summer–honestly its really hot up here! There are a lot of commercial datalogging machines out there but Alaska needed its own DIY brand: Waterproof, Two waterproof sensors on long lines that could be within the cache and another to lay on the surface, Something buildable for kids with a STEM program, Minimal maintenance, Long term battery, Easy download from SD card, 3D printable, rechargeable, Real time Clock, and cheap.
The design is totally printable with any 3D printer and I have done the design for the PCB that you can order and populate with easy to obtain components. The battery is generic 18650 that should last a year or so with 12x/day readings and charging is done by just plugging in some power for a day. It is designed(Fusion 360) around the O-ring that is used in house water purifiers so it is easy to obtain and with silicon grease and tightening of the well placed bolts should provide protection for the Alaska winter if it comes this year….
Step 1: Gather Your Supplies
The wonderful designs from Adafruit make up most of the components on the board–they are a little more expensive but they are very workable and dependable. ( I have no financial ties with any company…) I used a Creality CR10 printer for the 3D parts. The two switches are waterproof variety.
1. Vktech 5pcs 2M Waterproof Digital Temperature Temp Sensor Probe DS18b20 $2
2. Adafruit DS3231 Precision RTC Breakout [ADA3013] $14
3. Adafruit TPL5111 Low Power Timer Breakout $5
4. Adafruit Feather 32u4 Adalogger $22 You can also use the MO version but the battery level line is on a different pin and you must change it in the software.
5. IZOKEE 0.96” I2C IIC 12864 128X64 Pixel OLED $4
6. Rugged Metal On/Off Switch with Blue LED Ring – 16mm Blue On/Off $5
7. Rugged Metal Pushbutton with Blue LED Ring – 16mm Blue Momentary $5
8. A variety of quick connects to make assembly easy
9. 18650 Battery $5
10. Captain O-Ring – Whirlpool WHKF-DWHV, WHKF-DWH & WHKF-DUF Water Filter Replacement
Step 2: Build It
The design of the housing is built around the easily available o-ring from a standard Westinghouse whole house water filter. The ring slips into a silicon lubricated groove between the the two printed halves of the enclosure. The bottom of the enclosure has space for the 18650 battery and the two waterproof control switches–there is also a hole for the exit of the cables for the temp probes. The two files for the upper and lower halves are below.
The bottom section is completed by taking some 4 mm or equivalent size nylon bolts and removing their heads and cementing them into the support pillars that have been drilled to accommodate them. Use an appropriate length so that the nylon cap nuts on the top will just cover them when the two halves are joined. Both upper and lower sections must be printed with support. The upper section is completed by gluing in a round plastic window made from thin lexan.
Step 3: Wire It
The assembly of the PCB is fairly straightforward. I designed the board in Eagle and sent it to PCBway for manufacture–honestly it the cheapest thing ever. If you want to bug-wire it that is easily done just follow the circuit diagram on the Brd file. The small LED screen is attached through the I2C connections on the board along with power and ground. The heart of the system is the TPL5111 which is connected directly to the battery and stays on all the time. It has a selectable timer (variable resistor) that wakes the system up every 2 hours to every second by enabling the enable pin on the Feather module. The RTC communicates by the same I2C bus as the LED–they have different addresses. The Feather is also connected to the 18650 battery by JST cable through the on/off switch to turn all power off to the system. This allows built in charging by the Feather when the battery is low by plugging in a micro USB into the feather. Whenever you upload new software to the Feather you must remember to start the TPL5111 by pushing its button otherwise the Feather will not answer the USB boot call. The pushbutton is designed to provide power to the LED screen only when pushed and also to send a high signal to the TPL5111 that allows the Feather to turn on for as long as you have the button pushed. This is done to limit the amount of time the screen is on — it is used only to check the status of the temp probes, battery level and time/date and the size file that you are building. The last piece of wiring are the two probes that are placed through the last drill out spot on the lower half. These were connected with JST 3 pin connectors to make removal easier. I neglected to place the 4.7K resistor on the board to connect the Data and Voltage pin on the temp sensor bus. So this must be done on one of the sensor connection points on the board–they are labeled so it should be easy. They both go to the same GPIO pin on the Feather so only one resistor connection is necessary.
Read more: Alaska Datalogger