Introduction
Recently, I created a six-channel wireless metal detector transceiver, and it seems I’ve become interested in wireless control. In this issue, we will introduce the design and implementation of a ten-channel wireless relay controller.
The project aims to achieve button control of ten relays. The relays selected are industrial relays with a rated coil voltage of 12V and a load capacity of 80A. It resembles a remote control decoder.
However, I couldn’t find a decoder with ten buttons on Taobao, and I also need to create a control circuit. Therefore, I chose to use a microcontroller to make a ten-channel controller, planning to use the STM32F103C8T6 as the main control unit and the nRF24L01 as the communication module, similar to the previous project.
Since I have extra AMS1117 and 7805 voltage regulator chips as well as EL357N optocoupler modules, this design is quite similar to the previous project.
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Schematic Design
The first part of the schematic mainly includes the design of the STM32 main control unit and the nRF24L01 wireless module, as well as the power supply section responsible for reducing the 12V input voltage to the 3.3V voltage usable by the microcontroller.
The second part consists of the relay driver made up of optocouplers and transistors. The receiving end of the optocoupler and the transistor form a Darlington pair, which effectively increases the amplification factor and compensates for the insufficient driving capability of the optocoupler.
According to the manual, the driving capability of the optocoupler is only 50mA, while the relays I selected require a larger current, so additional amplifying transistors are needed.
The S8050 in SOT23 package can reach a collector current of up to 500mA, which is sufficient for our relay usage.
PCB Design
There are no special points to note for the PCB; the author’s drawing skills are not very strong. After testing, the ten-channel relay control works normally, with a full load current of about 0.8A, and the power consumption of ten relays working simultaneously is about 10W.