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Environmental NeTwork Sensor (ENTS) Node Hardware

Annotated Soil Power Sensor

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/UpNyCD2G 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.

Steps for assembly

  1. Order PCB, the included gerber files were generated for JLCPCB
  2. Order components from the BOM.
  3. Solder surface mount components, excluding the following
    • Wio-E5
    • Screw Terminals
    • Pin headers
  4. Solder remaining through hole components.
  5. Solder the AAA battery clips on the bottom of the board.
  6. Solder a jumper wire from J6 to the positive input power on the Wio-E5.

Clearing the bootloader

The Wio-E5 module comes pre-installed with LoRa AT command firmware with hardware write protection enabled. Before you are able to flash the device the read protection must be cleared using STM32CubeProgrammer using a ST-Link debugger. We prefer to use the STLINK-V3MINIE due to its small form factor and low cost.

  1. Start STM32CubeProgrammer
  2. Connect the device and ST-Link device.
  3. On the right panel configure the Port to SWD
  4. On the Wio-E5 module, hold BOOT, press and release RST, then release BOOT. You are now in the bootloader.
  5. In STM32CubeProgrammer press connect. It will give a Error: Data read failed popup. This is expected.
  6. Go to Option Bytes tab.
  7. Under Read Out Protection change RDP to AA.
  8. Press apply. You should get a Option Bytes successfully programmed popup.
  9. Press disconnect.
  10. Unplug and plug back in the soil power sensor.
  11. Flash firmware with pio run -t upload.

Testing

Shorts

Before powering on the board shorts to ground on any of the supply rails.. The continuity test on a multimeter may initially beep for a short period of time due to bypass capacitors. TP4 may display a resistance value due to internal capacitance. Ensure it is not close to zero.

Power Rails

Then, power the device through the USB-C terminal and flash with firmware that enables all the peripherals. Verify the voltages at the test points match what is shown in the table.

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
TP3 +3V3 +3.3V
TP4 -3V3 -3.3V
TP5 VCC 5V
TP7 VUSB 5V
TP8 VBAT N/A

Unit Tests

In the firmware repo run the unit tests for both stm32 and esp32 projects with the following commands from the respective folders:

pio test -e tests -i test_sdi12

The test test_sdi12 is ignored since it relies on external hardware that might not be connected. All tests should pass.

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.

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.

J5 (Power Select)

Jumper J5 selects the power source, either VUSB from the USB-C terminal or VBAT from the 4 x AAA batteries on the backside of the board. The jumper can also be used to power the board directly from a DC power supply.

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

License & Copyright

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

Maintainers