Building EMUs.md

Building EMUs

With the appropriate parts, you can build your own EMUs. Our video associated with the paper steps through this process, below is some additional information.

Soldering

Proper soldering takes some training or experience, and we recommend that those new to soldering educate themselves, especially on safety. Here is a video beginner tutorial, and a series of 9 video lessons(1 and 6 are especially relevant). At a minimum, we recommend safety goggles, good ventilation, a soldering iron tip cleaner, a clear workspace that keeps the cord away from the iron, and a sturdy soldering iron stand.

Sensors and the D1 Mini generally come without the pins soldered into the circuit board. Some (e.g. the D1 Mini) come with more than one pin type. We solder these on, using the long female pin headers for the D1 Mini. One could solder wires directly to the sensors, rather than these pins, however, we prefer the pins because it allows for easy sensor replacement.

Additionally, we make several small modifications to the pre-build sensor modules (see video, paper supplement):

1. Since the BME280, BH1750, ADS1115 and DS3231 all share the same I2C wires, the pullup resistors on the SCL and SDA lines present on all four modules are redundant, wasting some electricity. We remove those on the BH1750 (marked 472), and the DS3231 clock (4x472 block across from the VCC pin).
2. Removing the 4x472 block on the DS3231 clock also removes the pullup resistor on the SQW pin. Failure to remove this resistor prevents the clock SQW alarm pin from turning on the MOSFET switch.
3. We remove the resistor marked 102 on the DS3231SN clock (near SCL of the 4-pin header side). This resistor is for charging rechargeable LR2032 batteries, but we prefer to use non-rechargeable CR2032 batteries that are cheaper and last for years, and a charge current can degrade these batteries. See Ed Mallon and Beddows & Mallon 2018.

Breadboard Wiring Connections

Breadboards rows numbered from 1-30 and columns lettered from A to J. Within a row, holes A-F are connected to each other, and G-J are connected. Additionally, breadboards have 2 columns labeled (+) and (-) on each outer side. These columns or "rails" are usually used to distribute power. In our setup, the left rails (beside column A) are used for battery power. The right (+) rail (beside column J) is used for 3.3v power (from the D1 Mini), and the right (-) rail is unused.

To wire an EMU breadboard, plug in the wires denoted below, roughly in the order they appear using their row and column addresses, then the components. Generally, we use longer 10-30 cm wires to connect the BME280, BH1750, and soil moisture module to the breadboard, rather than plugging them in directly, but this can be specific to application.

Component	Start	End	Function	Notes
Wire	(-)	A2	Grounding for D1 Mini
Wire	(-)	A11	Grounding for D1 Mini	For redundancy
Wire	(+)	A13	Power to the MOSFET	Battery voltage
Wire	(-)	A22	Grounding for clock, BME280, ADS1115, & BH1750
Wire	(-)	A29	Grounding for soil moisture probe
Wire	B21	B28	Power for soil moisture probe	3.3v
Wire	B19	F23	Clock I2C - SCL line
Wire	B20	F24	Clock I2C - SDA line
Wire	C2	C11	Grounding for D1 Mini	For redundancy
Wire	E5	E22	Sensors & Clock I2C - SCL line
Wire	E6	E24	Sensors & Clock I2C - SDA line
Wire	E10	E14	Power from the MOSFET to the D1 Mini	Battery voltage
Wire	E15	E18	Clock alarm to the MOSFET	Turns power on
Wire	E21	F21	Power for soil moisture probe and clock	3.3v
Wire	E22	F22	Grounding for BME280, ADS1115, & BH1750
Wire	E30	F27	Soil moisture probe signal to ADS1115
Wire	F8	H6	Enables waking from sleep for D1 Mini	Clock failsafe
Wire	J1	(+)	Power to the right breadboard rail	3.3v; all sensors & clock
Wire	J21	(+)	Power to sensors & clock	3.3v
330k ohm Resistor	C1	F7	Measures battery voltage	Either orientation
Wire	D1	D10	Power from the MOSFET to the D1 Mini	Battery voltage
100k ohm Resistor	D13	D15	Pullup for MOSFET	Either orientation
100k ohm Resistor	J5	(+)	Pullup for code disable pin	Either orientation
NDP6020P P-MOSFET 3-pin	C13	C15	Power switch	Orientation matters: Source→C13, Drain→C14, Gate→C15
Lolin D1 Mini Microcontroller	B1/H1	B8/H8	The brains of the EMU	B1→5V, I1→3.3V
DS3231SN Module	D17	D22	Clock: timekeeping & power management	GND→D22, VCC→D21, SDA→D20, SCL→D19, SQW→D18
ADS1115 Module	I21	I30	Analog to digital converter for soil moisture	align VCC→I21
Soil Moisture Sensor Module	D28	D30	Soil moisture sensor	VCC→D28, GND→D29, AO→D30
BME280 Module	H21	H24	Temp/humidity sensor	VCC→H21, GND→H22, SCL→H23, SDA→H24
BH1750FVI Module	G21	G24	Light sensor	VCC→G21, GND→G22, SCL→G23, SDA→G24
4xAA Battery Pack	(+)	(-)	Battery power	Hook up (+) and (-) to the side adjacent to row A

Waterproofing

We recommend coating the circuit boards of the BME280 and BH1750 with MG Chemicals silicone modified conformal coating after soldering pins on. Be very careful not to cover the light sensor (black rectangle) on the BH1750 module or the humidity sensor hole (tiny hole in silver square) on the BME280 sensor. Coating internal components (especially higher value modules such as the D1 Mini) is a good idea as well. In the event of water leakage, these can be salvaged and reused. In our testing, this coating has the best weatherproofing capability. It can be painted on, removed with acetone, and coatings can be quality-checked using a UV light.

External wiring connections or pins cannot be coated with silicone conformal coating: this would prevent the connection. Therefore, for these we use Nano Protech nano-partical anti-corrosion spray. This spray works relatively well, but may need to be reapplied over long periods. We recommend keeping external wiring connections to the bare minimum. We experimented with shrink-wrap tubing to coat wiring connections, but instead these trapped water, making the problems worse.

Temperature Sensor Shielding

Temperature sensors should be shielded from the sun, and perhaps also from the ground to prevent elevated temperature reading. Ideally, shielding should be fan-aspirated, to prevent air from being trapped near the sensor. Alternatively, naturally aspirated gill shields, provide accuracy to within 1-2 °C when there is no wind to create air movement (and higher accuracy in other conditions). Unfortunately, both of these options are prohibitively expensive relative to EMUs.

Instead of buying a shield, we built one out of an inverted white plastic cup bottom, similar to Cowles et al. 2016. Subsequently, Terando et al. 2017 have done careful tests and concluded that this is not a good design and can even be worse than no shielding in some circumstances. Instead, they recommend one built by Holden et al. 2013 (video instructions for construction) out of corrugated plastic material covered with foil tape. This shield provides similar shielding to naturally-aspirated gill shields.

Regardless of the shielding used, we recommend that researchers carefully consider their shielding design, and if it has not already been tested against a high quality shield and temperature sensor, we recommend that this be done.

Lessons Learned from Novice Builders

In General:

• Orientation of sensors and pins should ALWAYS be checked before anything is added or removed.
• Each sensor or module should be tested separately to ensure it’s working properly before final assembly.
• Safety precautions should be thoroughly examined before each process.

Soldering:

• For anyone’s first time soldering it’s important to note how to properly hold the solder and soldering iron as well as to understand ventilation and safety concerns.
• Good ventilation (at least a fan) should be used while soldering. Safety glasses and aprons are advised.
• Looking up instructional videos explaining how to solder properly is advised for beginners. (Please see Soldering for more information/videos on soldering)
• The type of soldering tip is important. For removing resistors, a larger flatter tip was found to be easier rather than the common pencil type tip used for soldering pins.
• Always turn off the soldering iron when not in use.
• Orientation of pins should be triple checked before soldering.
• Be safe!

Wiring:

• Using pre-cut wires saves time, though it is not required.
• It is better to take your time when wiring the breadboard. After all of the components are added, it makes it more difficult to recheck the positioning of the wires.

Waterproofing:

• Make sure that when painting the sensors with the silicone conformal coating, the actual sensor portion of the components are not covered. For example, the area on the light sensor that actually does the sensing should not be covered. Shining UV light shows whether any coating has covered this area.
• Fume hoods and ventilation should be used when using waterproofing coatings or sprays.
• Heat shrink tubing should be pre cut and pay attention to the size used. Looking up instructional videos on how to properly and safely use a heat gun is advised. Alternatively, any flame source is sufficient, but safety still applies.