Setting up a configurable Radio Frequency Communication System Using Si-1062 wireless microcontroller

In the previous tutorial, basic fundamentals of the radio frequency communication were discussed. The previous tutorial explained concept of radio communication, modulation techniques, fundamental structure of RF transmitter and receiver and performance parameters for RF systems. In this tutorial, it’s time to get hands dirty by constructing an RF system in practice. There are many radio frequency modules available in the market. These modules are available in the form of RF transmitter and receivers. A transmitter device at one end and a receiver device at another end can successfully transmit information from one end to another, but it can be only one-directional data transfer. For example, 433 MHz RF modules are quite popular that come in receiver and transmitter pair.

To establish a bi-directional link, the circuit needs to be a combination of transmitter and receiver and that is called a transceiver. There are many transceiver modules and circuit designs available in the market. Most of these transceiver modules have fixed performance parameters. That means that they come with preset operational range, data rate and bandwidth. Such modules are handy to use when requirements for a radio communication project are limited and constant in nature. This may not be the case all times. A lot of times a radio communication project requires configurable radio frequency link. So, a project may require adjusting or increasing the operational range, set radio communication frequency and change data rate for data transfer. These performance parameters are also inter-dependent and altering one parameter eventually alters the another parameter as well. For experimenting and playing around the performance parameters of radio communication system, a configurable RF communication system needs to be set up.

For making configurable RF communication systems, there are wireless microcontrollers available. These microcontrollers operate in pair with a transceiver device in-built or on-board. Often, wireless microcontrollers are available along with the RF transceiver on single RF boards or have RF transceiver integrated on-chip. These RF boards can be purchased as RF transceiver modules or can be constructed on a PCB with the help of open-source RF PCB designs. A configurable RF device has basic functional blocks same as any common RF transceiver device, but their performance characteristics like frequency, transmission power, amplification, data rate etc. can be altered as per the requirement. The wireless microcontrollers with in-built RF transceiver can be programmed to particular configuration for establishing a RF Communication Link. A wireless microcontroller usually have the following building blocks as shown in the figure below –

Conceptually the microcontroller and the RF transceiver are independent units and operate exclusively. The RF transceiver is responsible for establishing and handling RF communication while it has programmable registers that can be controlled or programmed by the wireless microcontroller to set the configuration parameters of the RF link. The microcontroller has the job of setting the configuration parameter by changing the register’s values by passing configuration data serially to the RF transceiver and it is designed specifically to operate and manipulate data received or transferred over RF link. The wireless microcontroller and the RF transceiver communicate through a communication channel for serial data transfer. The data can be configuration parameters in the form of register names and values or actual information to be transferred or received. Usually, the same channel is utilized by the microcontroller for writing data to the transceiver which has to be transmitted and read the data from the transceiver which has been received.

There are many wireless microcontrollers available in the market from several vendors. One needs to make a careful choice while selecting a wireless controller. The following factors are most important considerations while selecting a wireless microcontroller –

– Operating voltage and maximum power consumption

– Range of RF frequencies or the allowed bandwidth in which the RF transceiver can operate

– Maximum possible transmitter power

– Maximum possible receiver sensitivity

– Maximum possible data rate

– Different types of modulation techniques available

– Availability of performance improving techniques like, CRC, Frequency hopping, Antenna diversity etc.

– Tools and support from the vendor

These factors must be considered taking into account the requirements of RF project and the cost limitations of the same. One must be keen to determine the required performance parameters like what is the range in which the RF system will be operating, what will be the frequency and bandwidth requirement for operating in that range, which modulation technique should be used and what is the data rate required of the radio system. Based on the decision making over these performance factors, a wireless controller should be selected that meets the maximum requirements, have optimum cost and reliability. There are many wireless microcontrollers from several reputed vendors. So the parameters mentioned above should be carefully compared before finalizing any selection.

There are RF microcontrollers or wireless microcontrollers available from Silicon Labs, Texas Instruments, NXP, Microchip, Renesas Electronics and a dozen of other vendors. The RF microcontrollers can be selected based on Core architecture, Operating frequency, Data bus width, ROM, RAM, clock frequency, ADC resolution, Operating voltage, Operating temperature range and chip package. The controller should be selected as per the requirements of the RF project and its application.

In this series, silicon labs Si-1062 is taken for the experiments. This wireless microcontroller uses an 8051 based microcontroller core and Silicon Lab’s Si4x6x transceiver. The microcontroller section and the RF transceiver section are separated inside the chip and the communication between them is made possible using SPI interface. It is through this SPI communication channel the microcontroller configures the RF transceiver and read or writes data from it. The controller has 64 Kb flash memory and 4 Kb RAM. The controller comes equipped with 10-bit analog to digital convertor, in-built temperature sensor, dual comparators, 11 general purpose input/output pins that also serve for UART, SPI and I2C interfaces, four 16-bit Counters/Timers and in-built Real Time Clock. The Si1062 can be operated in the frequency range of 142 to 1050 MHz which is in the ISM band. The Si – 1060 transceiver can have up to 1 Mbps data rate and receive sensitivity of -126 dBm. The transceiver has features like auto frequency control and automatic gain control. The operating voltage of the controller is 1.8 V to 3.6 V. The controller is designed for applications like telemetry, home automation, remote control, lighting control, smart metering, security systems and medical electronics.

The Silicon Labs also provides documents on programming guide along with PCB design and software tools to configure and program the device. The Si-1062 is available from Silicon Labs with a Wireless Development Kit (WDK), which includes a motherboard with programmer, LCD, switches etc. and a detachable RF Pico board. One can either purchase the WDK or manufacture the RF Pico board with the help of PCB design files available for free download. To program this wireless microcontroller Silicon Labs provides an IDE for coding and if the RF Pico board is used alone, it requires a programmer to download and debug the code. Another useful tool from Silicon Lab which helps in configuring the RF transceiver is WDS3.

In this series, RF Pico board along with a small circuit built on breadboard will be used for the RF experiments. The circuit built on breadboard simply has an LED indicator and include circuit connections with the power supply. A 3V supply is provided to the PCB by connecting two 1.5 V batteries in series. The Si-1062 has the following pin diagram –

The RF Pico board has the following PCB design –

The circuit built on the breadboard has the following schematics –

The RF experiments will be conducted using the Wireless Development Suite (WDS3) tool available from the Silicon Labs. The tool can be used to select the required RF parameters and generate a configuration file. This configuration file can then be used with the program to load the appropriate values to the registers to configure the RF transceiver. The RF transceiver Si4x6x has large number of registers and lot of calculations needs to be done before changing any single value. With the use of WDS3, changing the performance parameters become handy for a RF Communication System designer.

First download and install the IDE, software and drivers required for the programmer. Assemble the circuit on breadboard and open the WDS3. Now it’s time to conduct a simple packet transfer experiment with the default RF parameter settings not changed.

In the Wireless development Suite, click on ‘Simulate Radio’ button.

Select the Si-1062 RF microcontroller from the list of controllers in the next window –

Select the radio configuration application in the next window –

Select the “standard packet Tx” application in the next window and change the frequency to 868 Mhz. Click on the “Generate source” button. On clicking the “Generate Source” button, it will prompt whether to download the code or to generate the Configure File for RF parameters which can then be used along with a program. Save the Configure file only for now and use the code attached with this project to burn the RF Pico board.

The code attached in the tutorial provides basic platform in which anyone can try out different RF experiments, all needed is to use the Configure file got from the WDS3 and replace it with the radioconfig.h file in the code attached. Similarly generate configure file for the receiver.

Compile and burn Rx code in the RF Pico board which is supposed to be the receiver and compile and burn the TX code in the other RF Pico board which is supposed to be the transmitter. Power them using 1.5 V batteries in series. when the two Pico boards will be kept at a close distance the LED indicator will start blinking which indicates that RF link has been successfully established.

In this tutorial, it is already learnt that how RF link can be setup using Si-1062 RF controller and how user-defined frequency can be generated using wireless development suite. In the next tutorial of the series, the range of the RF communication system, setup in this tutorial will be examined. The next tutorial will be about playing around the RF configuration parameters which can be altered directly from the Silicon Labs Wireless Development Suite to increase or maximize the range of the RF system.