LoRa Soil Monitor Design Overview

0:27

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

162 days

please explain what J1 does.

aneraovd

@copilot please explain what J1 does.

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:

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.
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).
Pin 10 ("~~RESET~~") is tied to the "RST" net, which typically would be used to reset the microcontroller or another digital system.
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.
Pin 6 ("SWO/TDO") could be used for Serial Wire Output or Test Data Output, both of which are used for debugging purposes.
Pin 9 ("GNDDetect") is likely tied to ground.

Please note that true functionality might depend on the overall system design and implementation.

Someone is typing...

please explain what U2 does.

cambrownobiwankenobi131140

@copilot please explain what U2 does.

Someone is typing...

LoRa_DIO0

SWCLK

LED_G

SPI1_MOSI

LoRa_RST

SPI1_CS

SWDIO

SPI1_CS

BOOT0

LED_R

LoRa_DIO0

USART2_RX

SPI1_SCK

SPI1_MISO

LED_B

USART2_RX

USART2_TX

LoRa_RST

SPI1_MOSI

ANT

RST

sensor

USART2_TX

SWDIO

RST

SPI1_SCK

SWCLK

BOOT0

SPI1_MISO

Capacitance

1uF

3V3

Capacitance

1uF

Capacitance

10uF

3V3

Capacitance

1uF

3V3

LED1

Resistance

220 Ω

Resistance

220 Ω

Resistance

10KΩ

Resistance

10kΩ

BATT1

Resistance

220 Ω

IC1

create a high level mermaid block diagram of sensor, LoRa\_DIO0, C4, 3V3, SWCLK,...

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.

copilot

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

Diagram

Someone is typing...

Reviews

Ground
A common return path for electric current. Commonly known as ground.
jharwinbarrozo
20.5M
Net Portal
Wirelessly connects nets on schematic. Used to organize schematics and separate functional blocks. To wirelessly connect net portals, give them same designator. #portal
jharwinbarrozo
43.0M
Power Net Portal
Wirelessly connects power nets on schematic. Identical to the net portal, but with a power symbol. Used to organize schematics and separate functional blocks. To wirelessly connect power net portals, give them the same designator. #portal #power
jharwinbarrozo
11.4M
Generic Resistor
A generic fixed resistor ideal for rapid circuit topology development. Its footprint automatically adapts based on the selected package case code—supporting 0402, 0603, 0805, 1203, and many other standard SMD packages, as well as axial horizontal and vertical configurations. Save precious design time by seamlessly add more information to this part (value, footprint, etc.) as it becomes available. Standard resistor values: 1.0 ohm, 10 ohm, 100 ohm, 1.0k ohm, 10k ohm, 100k ohm, 1.0M ohm 1.1 ohm, 11 ohm, 110 ohm, 1.1k ohm, 11k ohm, 110k ohm, 1.1M ohm 1.2 ohm, 12 ohm, 120 ohm, 1.2k ohm, 12k ohm, 120k ohm, 1.2M ohm 1.3 ohm, 13 ohm, 130 ohm, 1.3k ohm, 13k ohm, 130k ohm, 1.3M ohm 1.5 ohm, 15 ohm, 150 ohm, 1.5k ohm, 15k ohm, 150k ohm, 1.5M ohm 1.6 ohm, 16 ohm, 160 ohm, 1.6k ohm, 16k ohm, 160k ohm, 1.6M ohm 1.8 ohm, 18 ohm, 180 ohm, 1.8K ohm, 18k ohm, 180k ohm, 1.8M ohm 2.0 ohm, 20 ohm, 200 ohm, 2.0k ohm, 20k ohm, 200k ohm, 2.0M ohm 2.2 ohm, 22 ohm, 220 ohm, 2.2k ohm, 22k ohm, 220k ohm, 2.2M ohm 2.4 ohm, 24 ohm, 240 ohm, 2.4k ohm, 24k ohm, 240k ohm, 2.4M ohm 2.7 ohm, 27 ohm, 270 ohm, 2.7k ohm, 27k ohm, 270k ohm, 2.7M ohm 3.0 ohm, 30 ohm, 300 ohm, 3.0K ohm, 30K ohm, 300K ohm, 3.0M ohm 3.3 ohm, 33 ohm, 330 ohm, 3.3k ohm, 33k ohm, 330k ohm, 3.3M ohm 3.6 ohm, 36 ohm, 360 ohm, 3.6k ohm, 36k ohm, 360k ohm, 3.6M ohm 3.9 ohm, 39 ohm, 390 ohm, 3.9k ohm, 39k ohm, 390k ohm, 3.9M ohm 4.3 ohm, 43 ohm, 430 ohm, 4.3k ohm, 43K ohm, 430K ohm, 4.3M ohm 4.7 ohm, 47 ohm, 470 ohm, 4.7k ohm, 47k ohm, 470k ohm, 4.7M ohm 5.1 ohm, 51 ohm, 510 ohm, 5.1k ohm, 51k ohm, 510k ohm, 5.1M ohm 5.6 ohm, 56 ohm, 560 ohm, 5.6k ohm, 56k ohm, 560k ohm, 5.6M ohm 6.2 ohm, 62 ohm, 620 ohm, 6.2k ohm, 62K ohm, 620K ohm, 6.2M ohm 6.8 ohm, 68 ohm, 680 ohm, 6.8k ohm, 68k ohm, 680k ohm, 6.8M ohm 7.5 ohm, 75 ohm, 750 ohm, 7.5k ohm, 75k ohm, 750k ohm, 7.5M ohm 8.2 ohm, 82 ohm, 820 ohm, 8.2k ohm, 82k ohm, 820k ohm, 8.2M ohm 9.1 ohm, 91 ohm, 910 ohm, 9.1k ohm, 91k ohm, 910k ohm, 9.1M ohm #generics #CommonPartsLibrary
jharwinbarrozo
1.5M
Generic Capacitor
A generic fixed capacitor ideal for rapid circuit topology development. You can choose between polarized and non-polarized types, its symbol and the footprint will automatically adapt based on your selection. Supported options include standard SMD sizes for ceramic capacitors (e.g., 0402, 0603, 0805), SMD sizes for aluminum electrolytic capacitors, and through-hole footprints for polarized capacitors. Save precious design time by seamlessly add more information to this part (value, footprint, etc.) as it becomes available. Standard capacitor values: 1.0pF, 10pF, 100pF, 1000pF, 0.01uF, 0.1uF, 1.0uF, 10uF, 100uF, 1000uF, 10000uF 1.1pF, 11pF, 110pF, 1100pF 1.2pF, 12pF, 120pF, 1200pF 1.3pF, 13pF, 130pF, 1300pF 1.5pF, 15pF, 150pF, 1500pF, 0.015uF, 0.15uF, 1.5uF, 15uF, 150uF, 1500uF 1.6pF, 16pF, 160pF, 1600pF 1.8pF, 18pF, 180pF, 1800pF 2.0pF, 20pF, 200pF, 2000pF 2.2pF, 22pF, 220pF, 2200pF, 0.022uF, 0.22uF, 2.2uF, 22uF, 220uF, 2200uF 2.4pF, 24pF, 240pF, 2400pF 2.7pF, 27pF, 270pF, 2700pF 3.0pF, 30pF, 300pF, 3000pF 3.3pF, 33pF, 330pF, 3300pF, 0.033uF, 0.33uF, 3.3uF, 33uF, 330uF, 3300uF 3.6pF, 36pF, 360pF, 3600pF 3.9pF, 39pF, 390pF, 3900pF 4.3pF, 43pF, 430pF, 4300pF 4.7pF, 47pF, 470pF, 4700pF, 0.047uF, 0.47uF, 4.7uF, 47uF, 470uF, 4700uF 5.1pF, 51pF, 510pF, 5100pF 5.6pF, 56pF, 560pF, 5600pF 6.2pF, 62pF, 620pF, 6200pF 6.8pF, 68pF, 680pF, 6800pF, 0.068uF, 0.68uF, 6.8uF, 68uF, 680uF, 6800uF 7.5pF, 75pF, 750pF, 7500pF 8.2pF, 82pF, 820pF, 8200pF 9.1pF, 91pF, 910pF, 9100pF #generics #CommonPartsLibrary
jharwinbarrozo
1.5M
Generic Inductor
A generic fixed inductor suitable for rapid circuit topology development. The footprint automatically adapts based on the selected package, supporting standard SMD sizes (e.g., 0402, 0603, 0805) as well as well-known inductor packages such as SDR1806, PA4320, SRN6028, and SRR1260. Standard inductor values: 1.0 nH, 10 nH, 100 nH, 1.0 µH, 10 µH, 100 µH, 1.0 mH 1.2 nH, 12 nH, 120 nH, 1.2 µH, 12 µH, 120 µH, 1.2 mH 1.5 nH, 15 nH, 150 nH, 1.5 µH, 15 µH, 150 µH, 1.5 mH 1.8 nH, 18 nH, 180 nH, 1.8 µH, 18 µH, 180 µH, 1.8 mH 2.2 nH, 22 nH, 220 nH, 2.2 µH, 22 µH, 220 µH, 2.2 mH 2.7 nH, 27 nH, 270 nH, 2.7 µH, 27 µH, 270 µH, 2.7 mH 3.3 nH, 33 nH, 330 nH, 3.3 µH, 33 µH, 330 µH, 3.3 mH 3.9 nH, 39 nH, 390 nH, 3.9 µH, 39 µH, 390 µH, 3.9 mH 4.7 nH, 47 nH, 470 nH, 4.7 µH, 47 µH, 470 µH, 4.7 mH 5.6 nH, 56 nH, 560 nH, 5.6 µH, 56 µH, 560 µH, 5.6 mH 6.8 nH, 68 nH, 680 nH, 6.8 µH, 68 µH, 680 µH, 6.8 mH 8.2 nH, 82 nH, 820 nH, 8.2 µH, 82 µH, 820 µH, 8.2 mH #generics #CommonPartsLibrary
jharwinbarrozo
15.8k
Terminal
An electrical connector acting as reusable interface to a conductor and creating a point where external circuits can be connected.
natarius
RMCF0805JT47K0
47 kOhms ±5% 0.125W, 1/8W Chip Resistor 0805 (2012 Metric) Automotive AEC-Q200 Thick Film #forLedBlink
jharwinbarrozo
1.2M
875105359001
10uF Capacitor Aluminum Polymer 20% 16V SMD 5x5.3mm #forLedBlink #commonpartslibrary #capacitor #aluminumpolymer #radialcan
jharwinbarrozo
1.2M
CTL1206FYW1T
Yellow 595nm LED Indication - Discrete 1.7V 1206 (3216 Metric) #forLedBlink
jharwinbarrozo
1.1M

Project Name

LoRa soil monitor Reference Design

Description

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

Properties

License

creativecommons.org/licenses/by/4.0/

Pricing & Availability

Distributor	Qty 1
Digi-Key	$8.35–$8.72
LCSC	$5.11
Mouser	$29.60

Controls

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vasyl / LoRa soil monitor Reference Design

Schematic