README.md

Environmental NeTwork Sensor (ENTS) Node Hardware

This repo contains the EagleCAD source files for the PCB design of the Soil Power Sensor. The Soil Power Sensor is a iteration on the design of CurrentSense by Lab11(https://github.com/lab11/CurrentSense).

BOM

The bill of materials is available digitally at https://octopart.com/bom-tool/nBygYAnz or as csv in hardware/Soil Power Sensor.csv.

There are two buttons not listed in the BOM for the esp32 BOOT and EN. These are cheaply available from amazon. Look for one with a 6mm by 6mm form factor.

Generate the BOM from the schematic editor (Tools -> Generate Bill of Materials...) and use the view Order.

Assembly and QA Instructions

Solder SMD components

We suggest ordering the boards SMD assembled through a PCB assembly service and have used JLCPCB in the past. Every component except the Wio-E5 module, 5-pin screw terminals, 3-pin screw terminals, and pin headers can be soldered by the assembly service. The component U13 should not be populated by default and is used to expand the non-volatile memory of sensor measurements.

Solder Remaining Components

Before soldering visually inspect the boards for any solder bridges and defects. You do not want to solder the Wio-E5 module to a defective board as it accounts for half the cost of the board and cannot be desoldered easily.

1. Solder screw terminals at J1, J4, male pin-headers at J3, female right-angle pin headers at J8, and female pin headers at J9.
2. Solder the Wio-E5 module to the board. The USB-C connector should be facing the edge of the board closest to the switch, and RF terminal facing the microSD card module. The RF terminal should touching the edge of the board.
3. Use a multimeter to test for shorts between GND and TP1, TP2, TP4, 5V on the Wio-E5, 3V3 on the Wio-E5, and Vcc on the 3-pin screw terminal. TP4 maay display a resistance value due to capacitors.

NOTE: J9 should be soldered with a female header to be used to connect a load. We did not have any 2x1 headers on hand so it is not shown in the picture.

Check Power Rails

Then, power the device through the USB-C terminal with the power switch in the "UP" (close to nearest board edge). Verify the voltages at the test points match what is shown in the table. Some rails may be put in power down state by default and require firmware to be running to enable them.

TP6 is used to used to connect the battery to the Wio-E5 module.

Test point	Signal	Voltage
TP1	REF+1V65	+1.65V
TP2	REF+3V3	+3.3V
3V3 (Wio)	+3V3	+3.3V
TP4	-3V3	-3.3V
TP5	VCC	5V
5V (Wio)	VUSB	5V

Load Firmware

See ENTS-node-firmware for instructions on loading firmware on the device.

Header definitions

D2 (STM32 SWD)

Serial wire debug (SWD) port for stm32. To load the bootloader, hold BOOT, press and release RST, then release BOOT. Then you should be able to connect to the device.

J9 (ESP32 Debug Header)

J3 (ESP32 UART)

UART TX and RX pins to connect to the esp32 bootloader. Intended to be use with a USB to UART converter and esptool.py.

J9 (Battery Connector)

Connect a battery module to the ENTS board. The header is reversible has the following pinout, where ~ represent inverse logic:

| GND | | 3V3 | | ~PG | | ~CHG | | VBAT | | VBAT | | ~CHG | | ~PG | | 3V3 | | GND |

Measurement configurations

The soil power sensor has multiple measurement configurations. The most common use case is Common GND which gives single ended measurements with low-side sensing.

Independent Inputs (Default)

Jumper	Bridged
JP1	No
JP2	No
JP3	No

Resistor	Value
Rsense1	DNP

Inputs Voltage, Current, GND are all independent from each other, therefore the most modular configuration. Use this mode when you want to measure a voltage/current difference that is not relative to GND. The GND connection must be connected to the common ground of the measured device.

Common GND

Jumper	Bridged
JP1	Yes
JP2	No
JP3	Yes

Resistor	Value
Rsense1	0 ohms

The negative terminals of Voltage and Current are tied to ground. Both measurements will be relative to ground. Connect common ground to the negative terminals or GND terminal.

Internal load

Jumper	Bridged
JP1	Yes
JP2	Yes
JP3	Yes

Resistor	Value
Rsense1	Any

The configuration uses a on-board resistor for RSENSE1. The resistor is chosen based on the desired range of input measurements. The board uses a high-side current measurements.

Userful links

Links for generating production files and BOM for JLCPCB

• Gerber and drill/map files
• BOM and centroid files

License & Copyright

The Soil Power Sensor board design files are licensed under the Solderpad Hardware License (wraparound license of Apache License).

Maintainers

• John Madden - jmadden173