LoraNet: accessing internet through lora (Hardware hackathon)
The Story
Recently Lora module has gained popularity among tinkerer. It is being used for weather station, disaster tracking, wildlife tracking and many other. Tinkerer myself got chance to use lora module during one of my freelance project. When I learned and implement lora, I was like that’s pretty cool. I mean you can send and receive data with in 10km radius(theoretically) without paying for any subscription and data packs, all you need is two lora modules which will cost you around couple of 700 NRs. But what made it possible? let’s take a peek in technical detail about lora.
First of all lora stands for (Long Range) communication and
Fundamentally it works same as other RF devices, but the technology
Use in LoRa communication separates it form other RF devices. RF
Device to send or receive signal need to be allocated with frequency
Band. Similarly LoRa device has also assigned fixed frequency band
According to the
region.
The key technology that enables LoRa to communicate at long range so
effectively lies in the modulation technique used by it knows as Chirp
Spread Spectrum. The symbols are represented as chirp and length of
the symbol is known as Spreading Factor(SF). You can change the
spreading factor of LoRa from 7-12. 7 begin the 7bits per symbol, less
window period for symbol means higher speed of communication but for
shorter distances. In contrary, 12 SF has more window period for
symbol which helps the receiver detect very weak signals from far away
in trade-off with speed. To know more about the CSS check out this
video by visual
electric.
While doing my freelance project a idea came to my mind what if we can access our home wifi with in 10km radius of your home. Suppose there is one LoRa module at home connected to internet via pi or ESP32. Another LoRa module with us far form fome, which we can somehow connect to mobile phone via USB or BLE, or using LoRa module as standalone handlheld device with display and control buttons. Then we can send data to home lora remotley, home LoRa further send request using internet, fetch the response and send back to us.
I told this idea to my friends. They thought its cool. But we didn’t implement back then due to some unforseen circumstance(our laziness). Almost a year after me and my juniors took part in hardware hackthon organized during Vector(National technical festival by our college WRC). It was open theme. So we decide to implement this idea.
Hardware Hacakathon
Me along with other three teammate Ritushwar Neupane, Prashant Bhandari, Safaraz Dewan took participated in 24 hours long hackathon. The goal was clear make two device Lora_home which will stay at home and Lora_out which will be used outside. The very first step was designing hardware, and the design of both device turns out to be identical and quite simple. ESP32 connected to LoRa module via SPI. ESP32 is connected to home wifi for Lora_home and ESP32 connect to mobile via BLE for Lora_out .
Both decive being identical opens a door to use both as messaging devices (like walkie-talkie). For this non of device need to connect to wifi.
Let’s take a moment of appreciation for Sarfaraz Dewan for this wonderful soldering.
The firmware and software
After building the hardware it was time to write some code. At first we wrote some testing code to test the communication between two Lora_devices and between mobile and Lora_out via BLE. We found out that maximum payload you can send and receive between two lora device is 255 bytes at time at Spreading Factor 7 and ~51 bytes at Spreading Factor 12. You might be thinking why only 255 bytes when SF is 7. The answer is that the register which hold the length of data is 8-bit. So the text greater than 255 byte, gets truncate itself. Anyways, to solve this problem we divided the text data into separate chunks of 200 bytes(safe side). And send one chunk at a time sequentially and simply receive sequentially and store in buffer to get final text data.
While testing our lora devices we were receiving some json data which was not sent by us, turns out another group was also doing lora based project and they were sending json data. Both theirs and ours lora had same configuration. To prevent this problem we designed our own custom packet. Every chunk we had header id RITU in the name of Ritushwar Neupane and RITUEND as marking the end of total chunk. And at the receiver side we parsed header ID(first fout bytes). If it is matched to RITU then read next bytes else discard.
//RITU+chunk1 ] first packet
//RITU+chunk2 ] second packet
//RITUEND ] end marker
//chunk1+chunk2=actaul data
void sendToLoRa(String response)
{
if (response.length() > 0)
{
mode = TX_MODE;
setMode(mode);
delay(100); // Increased delay before sending
int len = response.length();
int totalChunks = (len + CHUNK_SIZE - 1) / CHUNK_SIZE;
for (int i = 0; i < len; i += CHUNK_SIZE)
{
String chunk = response.substring(i, min(i + CHUNK_SIZE, len));
String fullPacket = "RITU" + chunk;
Serial.print("Sending chunk ");
Serial.println(fullPacket.substring(0, min(10, (int)fullPacket.length())));
LoRa.beginPacket();
LoRa.print(fullPacket);
LoRa.endPacket();
Serial.println("Chunk sent");
delay(500);
}
delay(500);
Serial.println("Sending END marker...");
LoRa.beginPacket();
LoRa.print("RITUEND");
LoRa.endPacket();
Serial.println("END marker sent");
Serial.print("Complete response sent: ");
Serial.println(response);
delay(100);
mode = RX_MODE;
setMode(mode);
}
}
After figuring out these basics we decide to implement three feature.
1. The walkie-talkie
Ability to message from one mobile through Lora_device like walkie talkie but in text. For this feature non of the Lora_decive need to connected to the wifi. You simply take the both Lora_device far from each other and connect it to mobile phone via BLE and then start communication.
2. Simple GPT(AI)
Using Lora_device to enable to prompt simple question to LLM like chat gpt or gemenie. For this feature Lora_home device need to be at home connected to wifi where as Lora_out device will be far from home connected to smartphone to prompt the LLM and get simple text answer.
3. Simple mail
Ability to send email to anybody even if you don’t have internet. The setup is same as Simple GPT feature. This is very useful in case of emergency.
In order to implement these feature we need a custom mobile app to communicate with Lora_device. So our another team mate Prashant Bandari and his agent developed a desired app which looks like this…
The app is connected to ESP32 via BLE and it only send text data to ESP32. ESP32 doesn’t know that received text data belogs to which feature itself. The app should encode some respective feature id so that ESP32 can parse it and find out what respective action to take at receiver end(Lora_home). After experimenting tons and rewriting logic again and again on both side we finally to a specific conclusion.
As you can see in the image above, the mail feature has MAIL as header id, then we simply update our logic to if first four bytes is RITU or MAIL then only read next byte else discard. Mail feature has three different packet design for recipients name, subject and body because we don’t use conventional way sending email. We need to send the info like recipients name, subject and body one by one sequentially.Then after that Lora_home device the put it all together and send mail. So to find out which text in mail is body or subject or recipients name, we implement their separate id.
These header_id and feature_id are attached by the app itself. Therefore, the Lora_out device need not add any overhead it simply passes the data to Lora_home which parse the data and take respective action. Moreover, the data receive by Lora_out from is mostly less than 255 bytes so no chunking of data is needed which reduces complexity.
The figure shows the complete data flow of the Simple GPT feature and it is pretty much self explanatory.
You can find full firmware of both device here and for app here.
Conclusion
It was quite fun experience to take part in hardware hackathon. Me and my junior Ritu vai and Prashant Vai woke up whole night coding both Lora_device. and sipping coffee The debugging and testing sessions were hilarious. Overall it was good experience.
About the project, I am thinking what if we can send real internet packets to the Lora_out device. I will research in this topic and continue to experiment if something comes up I will keep you updated.