XN04 - Temp-Hum / Lum
X-NODE Temp-Hum / Lum is a module that allows measurement of 3 environmental variables: Temperature, Humidity and Ambient Light. Ideal for IoT projects requiring control and monitoring of closed systems, such as air conditioning, refrigeration chambers, or automatic lighting adjustments. This module simplifies designs by reducing the need for multiple devices, offering a compact and efficient solution for monitoring applications.
TABLE OF CONTENTS
I. How does it work?
The X-NODE Temp-Hum / Lum is a module that combines 2 sensors: a SHT40 from Sensirion® for measuring ambient temperature/humidity and an LTR-329ALS from LITEON® for measuring indoor brightness. It also comes with an integrated controller, that allows you to obtain these variables using a series of ASCII commands.
X-NODE Temp-Hum / Lum is compatible with the mikroBUS™ standard from Mikroe® for easy use with a large ecosystem of hardware development kits, and also features JST connectors compatible with the Qwiic® standard from SparkFun® for quick and easy I2C communication between various modules and development boards.
II. Hardware description
SHT40 sensor from Sensirion®
JST connectors compatible with Qwiic®
LTR-329ALS sensor from LITEON®
Hardware controller
UART <> I2C communication ports
X-NODE model
X-NODE type
mikroBUS™ standard connectors
Jumper pad to enable native I2C communication* with the sensors.
Hardware version: R2
Main components on the X-NODE
III. Specifications
Type
Temperature, humidity, and ambient light sensor
Applications
Development of IoT systems requiring monitoring within closed systems, such as air conditioning, refrigeration chambers, or automatic lighting adjustments.
Module 1
Manufacturer
Module 2
Manufacturer
Features
* Temperature and humidity sensor with detection from 0 °C to 85 °C with typical accuracy of +/- 0.2 °C and +/- 1.8% RH, automatic calibration, 0.5 mA consumption, and high signal-to-noise ratio. * Ambient light sensor with detection from 0.01 to 64 klx, 50 Hz/60 Hz noise suppression, and typical consumption of 90µA.
Interface
UART, I2C
Compatibility
mikroBUS™ standard and Qwiic® standard
Size
41 x 25.4 x 20.5 mm
Voltage
3.3 V
IV. Pinout
The following table shows the pinout of the X-NODE Temp-Hum / Lum with respect to the mikroBUS™ standard (the latter is in the two center columns).
V. Usage
For easy and quick use of the X-NODE, you can use the ASCII command set provided by the integrated hardware controller via UART serial communication, or more advanced use via the I2C protocol.
UART Protocol
Configuration
UART communication uses the following configuration:
Baud rate: 115,200 bps
Parity: None
Data bits: 8
Stop bits: 1
Syntax
The UART protocol allows sending instructions in plain ASCII text. Each instruction consists of the X-NODE identifier, a command, and an end-of-line.
Identifier
The ID identifier is made up of the X-NODE model, which can be found at point 6 in the Hardware description section, and is complemented by an index, which can be a letter from A to Z, by default is A. To connect more than one module of the same model in a system, you must configure a unique identifier for each module, allowing up to 26 modules of the same model to be connected via UART protocol*.
Note: From this point on, the default index of the X-NODE Temp-Hum / Lum will be used for the rest of the manual: XN04A.
Command list
XN04A?
Checks if communication was established successfully. Response if successful: OK Response if error: XN04A=Error Example: XN04A=3 Error codes: 1: Temperature/humidity sensor error 2: Light sensor error 3: Both sensors errored
XN04A+V
Gets the current firmware version integrated in the X-NODE. Response: XN04A=Version Example: XN04A=2.0.0
XN04A+ID=(A-Z)
Changes the ID index to a different uppercase letter from A to Z. Once changed, you must use the new ID to change it again. Response: OK Example: XN04C+ID=H
XN04A+TW=(1-126)
Changes the factory I2C address to a different one, this only takes effect if the hardware driver is not disabled. The new address is written in decimal, selecting a value from 1 to 126. Response: OK Example: XN04A+TW=28
XN04A+GT
Gets the temperature value from the sensor. Returns the final value in °C with two decimals. Response: XN04A=VAL Example: XN04A=27.81
XN04A+GH
Gets the humidity value from the sensor. Returns a relative humidity (%) value. Response: XN04A=VAL Example: XN04A=80
XN04A+GL
Gets the light value from the sensor. Returns an ambient light value in Lux. Response: XN04A=VAL Example: XN04A=198
Advanced commands
XN04A+ETW=(0-1)
Enables (1) or disables (0) the device's I2C interface. Note: This setting is volatile, disconnecting power or sending the reset command will restore the I2C interface. Response: OK Example: XN04A+ETW=0
XN04A+SLP
Enables deep sleep mode to reduce power consumption, during deep sleep, the device will not respond to UART commands. To wake the device, send a logic low (0) to the WAKEUP/UPDI pin. Response: OK Example: XN04A+SLP
XN04A+RST
Resets the device, non-volatile values (e.g., ID, I2C address) are preserved, and volatile values return to default. Response: OK
XN04A+SP
Sets the temperature/humidity sensor precision to high (H)* (default), medium (M), or low (L), lower precision allows faster updates. Response: OK Example: XN04A+SP=L
XN04A+SH
Turns the humidity sensor heater on (1) or off (0). Use this if humidity readings are incorrect, enable the heater for at least 2 hours to repair the sensor. Response: OK Example: XN04A+SH=0
XN04A+SG
Sets the light sensor gain to 1 (1-64k lux, default), 2 (1-32k lux), 4 (1-16k lux), 8 (1-8k lux), 48 (1-1.3k lux), or 96 (1-600 lux), higher gain means lower range but higher precision. Response: OK Example: XN04A+SG=96
XN04A+SD
Turns the hardware controller for the sensors on (1) or off (0). Response: OK Example: XN04A+SD=1
XN04A+SN
Reads the serial number of the temperature and humidity sensor. Response: XN04A= Example: XN04A=4294900000
When reading temperature, humidity, or light, the following error responses may occur:
ERROR: Sensor communication error.
OL: Light value overflowed the register, set a lower gain if possible.
MEASURING: Sensor reading not finished, wait at least 20 ms for initialization.
HW_DRIVER_OFF: Hardware controller is not enabled.
End of line
The X-NODE will only respond to a command when a set of end-of-line characters are sent, each command must end with: <CR+LF>
CR means carriage return.
LF means line feed.
The combination <CR+LF> is a common way for computers to represent a new line, e.g., in a word processor to separate paragraphs.
For the X-NODE, <CR+LF> characters are used to identify the end of a command. If the identifier matches the node, the command exists, and it ends with <CR+LF>, the node will send a response.
Depending on your system, you must configure sending these characters differently.
UART Example Arduino Framework
#include "Arduino.h"
float getVariable( const char * command ){
// Clear the buffer
if (Serial2.available()) {
Serial2.read();
}
// Send the command
Serial2.print(command);
Serial2.println();
// Wait for a response
String variable_value = Serial2.readStringUntil('\n');
// If the response starts with the ID, communication was successful
if (!variable_value.startsWith("XN04A=")) {
Serial.println("Error");
return NAN;
}
// Convert ASCII value to decimal
return variable_value.substring(variable_value.indexOf('=') + 1).toFloat();
}
void setup() {
// Initialize serial monitor
Serial.begin(115200);
// Initialize UART communication on MikroBUS port
Serial2.begin(115200, SERIAL_8N1, 9, 10);
}
void loop() {
// Get environmental variable values
// Send command to get temperature
// \r\n represents <CR+LF> in C/C++
float temp = getVariable("XN04A+GT\r\n");
// Send command to get humidity
float hum = getVariable("XN04A+GH\r\n");
// Send command to get light
float lum = getVariable("XN04A+GL\r\n");
Serial.print("Temp: ");
Serial.print(temp);
Serial.println(" °C");
Serial.print("Hum: ");
Serial.print(hum);
Serial.println(" %");
Serial.print("Lum: ");
Serial.print(lum);
Serial.println(" lx");
delay(1000);
}I2C Protocol
To establish communication, you must know the I2C address of the X-NODE, the factory value is 0x04. I2C addresses are usually represented in hexadecimal, make sure to use the correct number system.
Configuration
Communication speed: 100 kHz - 400 kHz
Address: 7 bits
Write
To write to a register of the X-NODE Temp-Hum / Lum, the I2C controller must perform the following operations:
Send a start condition: The controller generates a logic low (0) on SDA while SCL remains high (1).
Send the X-NODE address: The controller sends the 7-bit address.
Send the operation type: The controller indicates if the operation is read (0) or write (1).
Wait for an acknowledge (ACK): The controller waits for a logic low (0) as confirmation (Acknowledgment) that a target with the sent address exists on the I2C BUS. If no response (1), there was a communication error or the address is incorrect.
Write n bytes of data: The controller writes n bytes in 8 bit (1 byte) sequences, MSB first. The target will send an ACK for each byte written.
Send a stop condition: The controller releases the I2C BUS by generating a logic high (1) on SDA while SCL is high (1).
Read
To read from a register of the X-NODE Temp-Hum / Lum, the I2C controller must perform the following operations:
Send a start condition: The controller generates a logic low (0) on SDA while SCL remains high (1).
Send the X-NODE address: The controller sends the 7 bit address.
Send the operation type: The controller indicates if the operation is read (0) or write (1).
Wait for an acknowledge (ACK): The controller waits for a logic low (0) as confirmation (Acknowledgment) that a target with the sent address exists on the I2C BUS. If no response (1), there was a communication error or the address is incorrect.
Read n bytes of data: The target will send n bytes in 8 bit (1 byte) sequences, MSB first, after receiving a byte, the controller must send an ACK to request another byte, or a NACK to indicate the end of transmission and request the target to release the BUS.
Send a stop condition: The controller releases the I2C BUS by generating a logic high (1) on SDA while SCL is high (1).
Register list
In an I2C target, registers are memory addresses that allow configuring or obtaining data from the target. There are two types of operations: read (R) and write (W).
TEMP
0x01
R
2
Gets the temperature value in °C*100, divide by 100 to get °C
HUM
0x02
R
2
Gets the relative humidity value * 100, divide by 100 to get percentage (0-100%)
LUM
0x03
R
2
Gets the ambient light (ALS) value in Lux
HEATER
0x04
R/W
1
Turns the humidity sensor heater on (1) or off (0). Use this if humidity readings are incorrect, enable the heater for at least 2 hours to repair the sensor.
PRECISION
0x05
R/W - NV
1
Sets the temperature/humidity sensor precision to high (3)* (default), medium (2), or low (1), lower precision allows faster data updates.
GAIN
0x06
R/W - NV
1
Sets the light sensor gain to 1 (1-64k lux, default), 2 (1-32k lux), 4 (1-16k lux), 8 (1-8k lux), 48 (1-1.3k lux), or 96 (1-600 lux). Higher gain means lower range but higher precision.
SERIAL_NUM
0x07
R
4
Reads the serial number of the temperature and humidity sensor
DRIVER
0x36
R/W - NV
1
Turns the hardware controller for the sensors on (1) or off (0)
STAT
0x37
R
1
XNODE status, 0x00 if no errors, any other value means communication error. Error codes: 1: Temperature/humidity sensor error 2: Light sensor error 3: Both sensors errored
FW
0x38
R
3
Firmware version, in major, minor, and patch: 0x02.0x00.0x00
UART_ID
0x39
R/W - NV
1
Reads and writes the ID index as a letter from A (0x41) to Z (0x5A)
TW_ADD
0x3A
R/W - NV
1
Reads and writes the device's I2C address from 1 (0x01) to 126 (0x7D). Requires a reset or a power-on sequence to be applied
UART_EN
0x3B
W
1
Enables (0x01) or disables (0x00) the device's UART interface
SLEEP
0x3C
W
1
Enables (0x01) or disables (0x00) deep sleep, the device will wake up if the master writes the device's I2C address on the BUS
RESET
0x3D
W
1
Writing 0x01 resets the device
WHO_AM_I
0x3E
R
2
First byte is the XNODE model, second byte is the hardware revision
Non-volatile registers (NV)
Non-volatile registers are stored in the device's EEPROM, meaning they retain their values even if the device is powered off.
TEMP, HUM, LUM register structure:
When reading temperature, humidity, or light, the following reserved values indicate errors:
0xFFFF: Sensor communication error.
0xFFFE: Light value overflowed the register, set a lower gain if possible.
0xFFFD: Sensor reading not finished, wait at least 20 ms for initialization.
0xFFFC: Hardware controller is not enabled.
I2C Example Arduino Framework
#include <Arduino.h>
#include <Wire.h>
void setup() {
// Initialize serial monitor
Serial.begin(115200);
// Set I2C communication pins
Wire.setPins( 12, 13 );
// Initialize I2C communication
Wire.begin();
}
void loop() {
// Get environmental variable values
float temperature;
float humidity;
int lum;
Wire.beginTransmission(0x04);
Wire.write(0x01);
if ( Wire.endTransmission() != 0) {
delay(1000);
return;
}
if (Wire.requestFrom(0x04, 2) != 2) {
delay(1000);
return;
}
// Divide by 100 to get value in Celsius
temperature = ( (Wire.read() << 8) | Wire.read() )/100.0f;
Wire.beginTransmission(0x04);
Wire.write(0x02);
if ( Wire.endTransmission() != 0) {
delay(1000);
return;
}
if (Wire.requestFrom(0x04, 2) != 2) {
delay(1000);
return;
}
// Divide by 100 to get value in percent relative humidity
humidity = ( (Wire.read() << 8) | Wire.read() )/100.0f;
Wire.beginTransmission(0x04);
Wire.write(0x03);
if ( Wire.endTransmission() != 0) {
delay(1000);
return;
}
if (Wire.requestFrom(0x04, 2) != 2) {
delay(1000);
return;
}
lum = ((Wire.read() << 8) | Wire.read());
Serial.print("Temperature:");
Serial.print(temperature);
Serial.println(" C");
Serial.print("Humidity:");
Serial.print(humidity);
Serial.println(" %");
Serial.print("Light: ");
Serial.print(lum);
Serial.println(" lx");
delay(1000);
}VI. Downloads
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