LoRa is a promising low-power, long range wireless transmission protocol developed by Semtech as part of the emergence of Internet of Things (IoT). Simply put, it is a method for sending data separate from WiFi, Zigbee or Bluetooth. Its low power consumption amidst very long range of transmission (up to 10 km) makes it a very good choice for microcontroller systems.
The E32-TTL-100 SX1278 LoRA Module
I managed to grab one of those LoRa modules that litter the market today. Mine’s a E32-TTL-100 module which is said to be based on Semtech’s SX1278. Here’s the specifications for the module:
- Module size:21*36mm
- Antenna type:Standard SMA antenna (FREE)
- Power supply:2.3V-5.5V DC
- Communication level:5.2V(max)
- Transmission distance:3000m(max)
- Maximum power:2dB(100mW)
- Air rates:2.4Kbps
- Emission current:130mA @ 100mW
- Receiving current:13.5mA @ Mode 0, Mode 1
- Sleep Current:2.0uA(M1=1,M1=0)
- Emission length:256 Byte
- Receive length:256 Byte
- Communication Interface:UART
- RSSI support:Yes
- Working frequency:410MHz-441MHz(Default 433MHz)
- Operating temperature:-30?~+85?
- Receiver sensitivity:-130dBm @ 1.2Kbps
A range of 3km! I doubt this is possible for non-LOS (line of sight) but let’s see.
The module has 7 pins as shown:
It’s UART-based so I think RXD, TXD (and of course VCC and GND) are self-explanatory. Let me try to explain the M0, M1, and AUX pins.
It turns out, M0 and M1 are used to set the modes of the module. There are four modes: normal, wake up, power-saving and sleep. Here’s a useful table:
|Normal||0||0||UART and wireless channel is good to go|
|Wake-Up||0||1||Same as normal but a preamble code is added to transmitted data for waking-up the receiver.|
|Power-Saving||1||0||UART is disable and wireless is on WOR(wake on radio) mode which means the device will turn on when there is data to be received. Transmission is not allowed.|
|Sleep||1||1||Used in setting parameters. Transmitting and receiving disabled.|
The AUX Pin
The AUX pin serves as a flag for checking if the data has been sent or when data have been received. It’s also used to check if the module is still in self-check procedure which happens during power-on and exit from sleep mode.
When the module is idle, the AUX pin stays high. If there is data is to be sent, the AUX pin stays low 2-3 ms prior to the data being sent to the transmit buffer. The AUX pin goes back to high if the transmit buffer is clear (i.e., the data has been sent wirelessly). Similarly, the AUX pin goes low when there is data on the receive buffer.
The logic states of AUX pin are summarized below:
As mentioned, when the module is in sleep mode (M0=M1=1), we can change some options like baud rate, UART format, etc. The commands for changing parameters must be sent using 9600 baud, 8N1.
The format for changing parameters is : 0xC0/0xC2 ADDH ADDL SPED CHAN OPTION. When you want the parameters to be saved to EEPROM, use 0xC0. Otherwise, use 0xC2. The rest are bytes with the following possible values:
|ADDH||Module high address byte (00h by default)|
|ADDL||Module low address byte (00h by default)|
|SPED||UART Baud Rate and Air Data Rate||See bit descriptions below.|
|CHAN||Operating Frequency (0x00 to 0xFF corresponding to 410 to 441 MHz. Default is 0x17 - 433 MHz)|
|OPTION||Other options||See bit descriptions below.|
SPED Bit Descriptions
|Bit 7 and 6||Bit 5, 4, 3||Bit 2, 1, 0|
|UART Parity||UART Baud Rate||Air Data Rate|
11：8N1（equal to 00）
110：19.2kbps(equal to 101)
111：19.2kbps(equal to 101)
OPTION Bit Descriptions
|Bit 7||Bit 6||Bit 5,4,3||Bit 2||Bit 1 and 0|
|Fixed Transmission||I/O Drive Mode||Wireless Wake-up Time||FEC (Forward Error Correction) Switch||Transmission Power|
|0: transparent transmission (default)
1: fixed transmission (first three bytes can be used as high/low address and channel)
|0: TXD, RXD, AUX are open-collectors
1: TXD, RXD, AUX are push-pulls/pull-ups
|0：Turn off FEC
1：Turn on FEC（Default）
So for example, you want to change the UART baud rate to 115200, 8N1 mode, air data rate to 19.2kbps, use the default 433 MHz operating frequency, fixed transmission mode, push-pull pins, 250 ms wake-up time, FEC on, and 20 dBm transmission power. Set M0 and M1 and send the following data through UART:
0xC0 0x00 0x00 0x3D 0x17 0xC4
For reading the current options, send the commands:
0xC1 0xC1 0xC1
This is for reading the version number:
0xC3 0xC3 0xC3
And for resetting the module:
0xC4 0xC4 0xC4
Bob Chan has created an example sketch for using the E32-100 LoRa module with the Arduino. The library is available at his github repository. His library allows you to change parameters as I have discussed.
To use the above library, follow this connection:
|D10(Rx)||<---> 4.7k Ohm <--->||Tx|
|D11(Tx)||<---> 4.7k Ohm <--->||Rx|
I hope you found this tutorial useful. If you have questions, kindly drop a comment below.