Arduino Wireless Communication: Remote Help Device

Introduction

During the Mid-Autumn Festival when I visited my grandmother, I heard her mention that sometimes she falls in her bedroom and cannot get up for a long time.

The fixed telephone provided by the neighborhood committee is installed outside the bedroom, which means that my grandmother cannot call her uncle living on the second floor when she falls.

After understanding the situation, I decided to design a remote control for my grandmother, where pressing a button can trigger a relay connected to a constant power supply next to the anti-theft door, which will then send an amplified signal to the receiver on the second floor, causing the receiver to light up a red LED when it receives the signal.

According to the plan, the transmitter first sends a signal to the relay using a low-power device in the 2.4GHz frequency band, and the relay then transmits the signal to the second floor’s receiver using the more power-consuming 433MHz frequency band.

nRF24L01 2.4GHz Communication Module

However, after several days of attempts, I still could not achieve communication in the 2.4GHz band using the nRF24L01 module.

In the end, I could only use the 433MHz module to transmit and receive signals. The relay part of the project was also canceled.

FS1000A Signal Transmitter Module (Left) and Receiver Module (Right)

Theoretical Preparation – Hardware Part

This experiment uses the 433MHz band to achieve short-distance communication. The signals in this band have good penetration and diffraction capabilities, but the data transmission speed in this band is relatively low. Based on these characteristics, signals in this band are suitable for transmitting small amounts of data over longer distances.

Wave Diffraction Phenomenon

I purchased the FS1000A module online to transmit signals. This module has three pins corresponding to signal, power supply, and ground. The power input of the module accepts voltages from 2-12V, so I used the 5V port on the development board to power the module.

After inserting the module’s header pins into the breadboard, I connected the signal line to port 3 of the development board, then connected the power and ground, and the module was installed.

Experimental Wiring Diagram

The 433MHz receiver module has four pins. Among them, both data ports are connected to the same signal source, so only three wires need to be connected. After connecting its power, ground, and signal line to the Arduino Leonardo, the hardware responsible for signal transmission and reception is assembled.

To allow the signal to transmit further, I plan to solder an antenna to the reserved antenna holes (ANT) on the module. The wavelength of the 433MHz signal is 0.693 meters, so the length of the matching antenna should be 1/4 of the wavelength.

The spiral antenna in the upper right corner can expand the signal coverage

Based on this, we can calculate that the length of the antenna is 173mm. To further reduce the size, we can coil the antenna into a spiral shape.

Since the remote control is to be carried by the elderly, I need a lightweight power supply to power the development board. The Arduino UNO can be powered through USB, DC socket, and Vin pin.

I ruled out the less stable power bank and the disposable 9V rectangular battery, ultimately choosing a rechargeable 7.4V lithium battery as the power supply, connected to the development board through the Vin pin.

7.4V Polymer Lithium Battery

Theoretical Preparation – Software Part

I used the VirtualWire library to control communication in the 433MHz band. After configuring the environment, I found publicly available code online to test the performance of wireless communication.

In the program initialization part, I need to define a buffer to temporarily store information, while setting the port number and transmission rate for sending information.

In the main loop, I can call the vw_send() function to send the contents of the buffer. Finally, the program pauses for 10 milliseconds to ensure that all data is sent.

Code for Sending Signals

Experimental Process – Hardware Part

After the antenna arrived, it was time for assembly. First, I fixed the circuit board with a vise, applied a small amount of solder to the antenna hole with a soldering iron; then, I used tweezers to hold the antenna (to avoid burns), melted the solder again with the soldering iron, and inserted the antenna leg into the connector. Finally, I just had to adjust the antenna and wait for the solder to solidify to complete the task.

After assembling the signal transmission and reception module, the next issue was power supply. The battery I purchased used an XH2.54 connector, which could not connect to the circuit. Therefore, I found an XH2.54 socket and jumper wires, and created a conversion head with a soldering iron, successfully solving the power supply issue.

Homemade Conversion Head

Experimental Process – Software Part

Initially, I tried using the method mentioned in the “Experimental Process – Software Part” to solve the communication problem in the 2.4GHz band, but even after using the sample code and following the connection diagram, my relay still could not receive signals.

After encountering this issue, I switched three or four development boards to try, connecting and disconnecting the seven wires connected to the nRF24L01 repeatedly. However, ultimately my progress remained at the stage of transmitting signals, and the receiving module never received any signals.

References

1. Arduino 433Mhz virtualWire radio example 2019 library range. (n.d.). Retrieved 7 October 2024, from http://www.electronoobs.com/eng_arduino_tut99.php

2. Arduino NRF24 example 2019 library range. (n.d.). Retrieved 7 October 2024, from http://www.electronoobs.com/eng_arduino_tut95.php

3. LPD433. (2024). In Wikipedia. https://en.wikipedia.org/w/index.php?title=LPD433&oldid=1237652397

4. Lithium Polymer Battery. (2024). In Wikipedia. https://zh.wikipedia.org/w/index.php?title=%E9%8B%B0%E9%9B%A2%E5%AD%90%E8%81%9A%E5%90%88%E7%89%A9%E9%9B%BB%E6%B1%A0&oldid=83057642