LoRa Soil Monitor Design Overview

flux

Short answer: this design conditions a sensor signal with the MAX40005 and reads it on the MCU.
From the schematic:
  • Sensor input path:
    • The soil probe connects at the IN net portal, then through R5 to the nano-power amplifier/comparator IC1 input (Net 22 → IC1:IN).
    • The amplifier’s output (IC1:OUT) is on Net 17, which goes to the MCU’s PA8 pin on U2. C3 is tied to that path (to OUT and GND) to filter noise.
    • C4 provides local rail decoupling for the analog stage.
What this implies functionally:
  • The soil probe changes its electrical characteristics with moisture (typically resistance or conductivity). That varying signal is presented through R5 into IC1.
  • IC1 conditions it and produces a clean logic/analog level the MCU can read on PA8. With suitable firmware, PA8 can:
    • Use a digital threshold (treat IC1 as a comparator) for wet/dry or multi-level thresholding.
    • Or sample as an analog input (if PA8 is configured as ADC on L0 variant) for quasi-analog moisture level, depending on MCU pin capabilities chosen in firmware.
Important caveats:
  • I do not see an explicit AC excitation or true resistive bridge that is common for corrosion-free soil sensing. As-is, this likely uses a simple DC-based measurement, which can work but may cause probe electrolysis over time.
  • There is no obvious sensor connector net labeled specifically for a two-electrode probe except the IN line plus GND. That suggests a single-ended measurement versus ground.
If you share how your probe is connected (two-wire resistive vs. capacitive pad), I can recommend:
  • For resistive probes: low-duty-cycle AC excitation via GPIO and measure with an RC/ADC method to reduce electrolysis, plus input protection.
  • For capacitive probes: drive an excitation signal and measure amplitude/phase or frequency using a timer/capture pin, or add a simple relaxation oscillator front end.
Would you like me to propose a concrete sensing front end and firmware readout approach for your specific probe type?
Ask about probe type
Request improved analog front end
Ask for AC excitation approach
Clarify MCU measurement method
Add connector and protection
please explain what J1 does.
2y
aneraovd

aneraovd

@copilot please explain what J1 does.
2y

copilot

J1 is a connector, with the specific model being FTSH-105-01-L-DV-007-K, which is manufactured by Analog Devices. Connectors are hardware interfaces used for linking various electronic components together, providing the ability for electric current to flow between different regions of a circuit.
In the context of this project, J1 plays a vital role in enabling various functionalities. It has several pin connections, each with a specific role. Here are key pins and their functionalities:
  1. Pins 1, 3, 5 are all tied to the main power rail 3V3, supplying the board and its components with the required power. Pin 1 is "VTref" (voltage reference), which indicates this pin might be used for setting a reference voltage for the system.
  2. Pin 2 ("SWDIO/TMS") and Pin 4 ("SWDCLK/TCK") are connected to the SWDIO and SWCLK nets respectively. These are most likely used for Serial Wire Debug (SWD) interface which is used for debugging and programming the microcontroller (U2: STM32L031G6U6S).
  3. Pin 10 ("RESET") is tied to the "RST" net, which typically would be used to reset the microcontroller or another digital system.
  4. Pin 8 is named "NC/TDI", where NC usually denotes 'Not Connected', and TDI stands for "Test Data In" used in JTAG interface but since it's labeled as 'NC', it might not be used in this context.
  5. Pin 6 ("SWO/TDO") could be used for Serial Wire Output or Test Data Output, both of which are used for debugging purposes.
  6. Pin 9 ("GNDDetect") is likely tied to ground.
Please note that true functionality might depend on the overall system design and implementation.
2y
Someone is typing...
2
please explain what U2 does.

cambrownobiwankenobi131140

@copilot please explain what U2 does.
1y
Someone is typing...
4
C4
Capacitance
1uF
LED1
J1
C3
Capacitance
1uF
C2
Capacitance
10uF
C1
Capacitance
1uF
R4
Resistance
220 Ω
R2
Resistance
220 Ω
R3
Resistance
10KΩ
U2
R5
Resistance
10kΩ
R1
Resistance
220 Ω
BATT1
IC1
U1
3
create a high level mermaid block diagram of sensor, LoRa\_DIO0, C4, 3V3, SWCLK,...
hinduraorohit1111

hinduraorohit1111

@copilot create a high level mermaid block diagram of sensor, LoRa_DIO0, C4, 3V3, SWCLK, LED1, LED_G, SPI1_MOSI, 3V3, 3V3, LoRa_RST, SPI1_CS, SWDIO, SPI1_CS, J1, BOOT0, LED_R, J2, LoRa_DIO0, USART2_RX, C3, SPI1_SCK, R4, SPI1_MISO, LED_B, R2, R3, USART2_RX, U2, R5, USART2_TX, C2, LoRa_RST, 3V3, SPI1_MOSI, IN, J4, LED_R, ANT, RST, sensor, USART2_TX, LED_G, LED_B, BATT1, 3V3, C1, R1, IC1, SWDIO, RST, 3V3, 3V3, SPI1_SCK, 3V3, U1, SWCLK, BOOT0, SPI1_MISO. Include key component's manufacturer part number in each block whenever possible.
2y

copilot

Sure, here is the high-level block diagram using Mermaid syntax with the corrected math delimiters:
Diagram



  
    
  
  
    
  



Components



























































sensor
LoRa_DIO0
C4<br>Capacitance: node_1u
3V3
SWCLK
LED1<br>MPN: 19-237/R6GHBHC-A04/2T<br>Everlight Elec
LED_G
SPI1_MOSI
3V3
3V3
LoRa_RST
SPI1_CS
SWDIO
SPI1_CS
J1<br>MPN: FTSH-105-01-L-DV-007-K<br>Analog Devices
BOOT0
LED_R
J2
LoRa_DIO0
USART2_RX
C3<br>Capacitance: node_1u
SPI1_SCK
R4<br>Resistance: 220
SPI1_MISO
LED_B
R2<br>Resistance: 220
R3<br>Resistance: node_10K
USART2_RX
U2<br>MPN: STM32L031G6U6S<br>STMicroelectronics
R5<br>Resistance: node_10k
USART2_TX
C2<br>Capacitance: node_10u
LoRa_RST
3V3
SPI1_MOSI
IN
"J4<br>MPN: S4B-PH-SM4-TB(LF)(SN)<br>JST Sales America Inc."
LED_R
ANT
RST
sensor
USART2_TX
LED_G
LED_B
BATT1<br>MPN: node_1070TR<br>Keystone Electronics<br>Voltage: node_3V
3V3
C1<br>Capacitance: node_1u
R1<br>Resistance: 220
IC1<br>MPN: MAX40005ANS02+T<br>Analog Devices Inc./Maxim Integrated
SWDIO
RST
3V3
3V3
SPI1_SCK
3V3
U1<br>MPN: RFM95W-915S2<br>Hoperf letrnc
SWCLK
BOOT0
SPI1_MISO
2y
Someone is typing...
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LoRa soil monitor Reference Design

LoRa soil monitor Reference Design thumbnail
This is a LoRa soil monitor Reference Design. It uses a STM32L031G6U6S microcontroller and a RFM95W-915S2 LoRa transceiver, integrated with sensor interfacing and LED indicators. Communication occurs via USART and SPI. The system is powered using a battery. #referenceDesign #simple-embedded #stm #template #reference-design

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