What it shows
Wi-Fi does not reach farms, dams or hill villages. LoRa radio reaches kilometres on a few milliwatts. The project builds a transmitter that sends soil moisture and temperature and a receiver that shows them, then measures signal strength, packet loss and range against distance, spreading factor and antenna height.
The science
LoRa uses chirp spread spectrum, which trades data rate for sensitivity. A higher spreading factor (SF7 to SF12) gives longer range and lower data rate. Received signal strength (RSSI) falls with distance by roughly the path loss law, and signal-to-noise ratio (SNR) tells how close the signal is to the noise floor. Free-space range also depends on antenna height and obstructions.
Materials
Cost: under Rs 5,000. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Two ESP32 boards
- Two SX1278 LoRa modules for the 433 MHz licence-free band or ready 868 or 865 MHz boards approved for India (check the allowed band)
- Two matching antennas
- A soil moisture sensor and a DHT22
- Two power banks
- A phone with a GPS distance app
- A small box for the transmitter
Safety
For this project: Use only the licence-free band and power allowed in India and keep to the power limit of the module. Do not transmit near an airport. An adult must accompany field tests and keep to open safe ground.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
12 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Study the module datasheet, the allowed frequency and power in India and write down the settings you will use.
Wire the SX1278 to the ESP32 over SPI with 3.3 V supply and fit the antenna before powering it.
Install a LoRa library and run the sender and receiver example sketches on the bench.
Write the transmitter code that reads the sensors, forms a packet with node id, a counter, moisture and temperature and sends it every 10 seconds.
Write the receiver code that prints the packet, RSSI and SNR on the serial monitor and an OLED display.
Add a packet counter check in the receiver to count lost packets.
Walk or ride away in a straight line in open ground, stopping at 50, 100, 200, 500 and 1,000 metres and recording 30 packets at each point.
Repeat at SF7 and SF12 and again with the antenna held at 1.5 m and at 3 m.
Repeat in a built-up area to see the effect of buildings.
Plot RSSI against distance and packet loss against distance for each setting.
Compare with the free-space path loss formula and estimate the path loss exponent.
Write the report with the system design, field data, graphs, and a plan for a real farm deployment.
What you should see
The link works at 1 km or more in open fields at SF12 and falls much sooner in a town. The RSSI graph decreases steadily with distance, and packet loss rises when RSSI approaches about -120 dBm.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Why does LoRa reach further than Wi-Fi?
Spread spectrum modulation allows reception of very weak signals, at the cost of a low data rate.
2What is RSSI?
Received signal strength indicator, a measure of the received power in dBm.
3What happens at a higher spreading factor?
Range improves but each packet takes longer, so the data rate and battery use change.
4Why is the antenna height important?
It improves the line of sight and reduces ground and obstruction losses.
Take it further
Add a third node and a simple repeater and test whether a hilltop relay reaches a hidden valley.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.