IoT Connectivity in Rural India: A 600-Day Field Test

Connecting a sensor in a lab is easy. Connecting one in a remote farm with spotty 2G and frequent power cuts is a nightmare. This is the story of how we kept a soil moisture node alive for 600 days on a single battery.

1. The Hardware Bill of Materials (BOM)

We chose components based on three criteria: Availability in local markets, cost, and power consumption.

Component	Role	Approx Cost (INR)
PIC16F877A	Main Controller (Low Power)	₹180
SX1278 (Ra-02)	LoRa Module (433MHz)	₹350
SIM800L	GSM/GPRS Gateway	₹250
TP4056 + 18650	Battery Management	₹150

2. Choosing the Link: LoRa vs GSM

We used a Star Topology.
Nodes: 10x Sensor Units. Protocol: LoRa (Long Range). Range: 5km.
Hub: 1x Central Gateway. Protocol: GSM (2G). Uploads to Cloud.

Connectivity Protocol Comparison

Why LoRa? We evaluated every major IoT connectivity standard. Here's the decision matrix that drove our choice.

Packet Loss & Retry Strategy

In the real world, LoRa packets get lost. Weather, terrain, and interference all contribute. We implemented a lightweight ACK-based retry protocol at the application layer.

// Application-layer retry logic (Gateway side)
#define MAX_RETRIES 3
#define ACK_TIMEOUT_MS 5000

void receive_with_ack(uint8_t* buffer) {
    int retries = 0;
    bool ack_received = false;
    
    while (!ack_received && retries < MAX_RETRIES) {
        LORA_Receive(buffer);
        
        // Validate CRC
        if (validate_crc(buffer)) {
            LORA_Send_ACK(buffer->node_id);
            ack_received = true;
            store_reading(buffer);
        } else {
            retries++;
            delay_ms(ACK_TIMEOUT_MS);
            LORA_Request_Retransmit(buffer->node_id);
        }
    }
    
    if (!ack_received) {
        log_error("Node %d: packet lost after %d retries", 
                  buffer->node_id, MAX_RETRIES);
    }
}

3. The Critical "Deep Sleep" Code (Embedded C)

To survive on a single 18650 battery for months, we maximize sleep time. The duty cycle is < 0.1%.

// XC8 Compiler for PIC16F
void main() {
    SYSTEM_Initialize();
    
    while(1) {
        // 1. Wake up and Read Sensor
        ADC_Init();
        int moisture = ADC_Read(0);
        
        // 2. Transmit via LoRa (SPI)
        LORA_Send(moisture);
        
        // 3. Enter Deep Sleep
        // Shut down peripherals
        ADC_OFF();
        SPI_OFF();
        
        // Sleep for 30 mins (Watchdog Timer)
        for(int i=0; i<30; i++) {
           SLEEP(); // ~60s WDT timeout
        }
    }
}

4. Power Budget Calculation

Engineering is math. Here is why our system works.

5. Field Lessons

The biggest lesson? Rats love cables. We lost two sensor nodes because field rats chewed through the moisture sensor wires. We had to armor all cabling in PVC pipes for the final deployment.

Weatherproofing & Enclosure Design

Electronics in an open field face dust, rain, extreme heat (45°C+), and curious animals. Our IP65-rated enclosure used a "breathable" silicone gasket design — waterproof but allowing pressure equalization to prevent condensation.

• Enclosure: ABS plastic box (IP65), ₹80 from local electronics market
• Cable entry: PG7 cable glands with silicone seals
• Antenna: External SMA antenna mounted on top, pointing upward for maximum LoRa range
• Heat management: White enclosure paint to reflect sunlight, internal temperature never exceeded 55°C

---