Tag Archive | "RF"

RF Wireless Data with the Seeedstudio RFbee

Introduction

In this article we examine the Seeedstudio RFbee Wireless Data Transceiver nodes. An RFbee is a small wireless data transceiver that can be used as a wireless data bridge in pairs, as well as a node in mesh networking or data broadcasting. Here is an example of an RFbee:

You may have noticed that the RFbee looks similar to the Xbee-style data transceivers – and it is, in physical size and some pinouts, for example:

comparison

However this is where the similarity ends. The RFbee is in fact a small Arduino-compatible development board based on the Atmel ATmega168 microprocessor (3.3V at 8MHz – more on this later) and uses a Texas Instruments CC1101 low-power sub1-GHz RF transceiver chip for wireless transfer. Turning over an RFbee reveals this and more:

But don’t let all this worry you, the RFbee is very simple to use once connected. As a transceiver the following specifications apply:

  • Data rate – 9600, 19200, 38400 or 115200bps
  • Adjustable transmission power in stages between -30dBm and 10 dBm
  • Operating frequency switchable between 868MHz and 915MHz
  • Data transmission can be point-to-point, or broadcast point-to-many
  • Maximum of 256 RFbees can operate in one mesh network
  • draws only 19.3mA whilst transmitting at full power

The pinout for the RFbee are similar to those of an Xbee for power and data, for example:

There is also the ICSP pins if you need to reprogram the ATmega168 direcly with an AVRISP-type programmer.

Getting Started

Getting started is simple – RFbees ship with firmware which allows them to simply send and receive data at 9600bps with full power. You are going to need two or more RFbees, as they can only communicate with their own kind. However any microcontroller with a UART can be used with RFbees – just connect 3.3V, GND, and the microcontroller’s UART TX and RX to the RFbee and you’re away. For our examples we will be using Arduino-compatible boards. If Arduino is new to you, consider our tutorials first.

If you ever need to update the firmware, or reset the RFbee to factory default after some wayward experimenting – download the firmware which is in the form of an Arduino sketch (RFBee_v1_1.pde) which can be downloaded from the repository. (This has been tested with Arduino v23). In the Arduino IDE, set the board type to “Arduino Pro or Pro Mini (3.3V, 8MHz) w/ATmega168”. From a hardware perspective, the easiest way to update the firmware is via a 3.3V FTDI cable or an UartSBee board, such as:

xbs4

You will also find a USB interface useful for controlling your RFbee via a PC or configuration (see below). In order to do this,  you will need some basic terminal software. A favourite and simple example is called … “Terminal“. (Please donate to the author for their efforts).

Initial Testing

After connecting your RFbee to a PC, run your terminal software and set it for 9600 bps – 8 – None – no handshaking, and click the check box next to “+CR”. For example:

term1

Select your COM: port (or click “ReScan” to find it) and then “Connect”. After a moment “OK” should appear in the received text area. Now, get yourself an Arduino or compatible board of some sort that has the LED on D13 (or substitute your own) and upload the following sketch:

Finally, connect the Arduino board to an RFbee in this manner:

  • Arduino D0 to RFbee TX
  • Arduino D1 to RFbee RX
  • Arduino 3.3V to RFbee Vcc
  • Arduino GND to RFbee GND
and the other RFbee to your PC and check it is connected using the terminal software described earlier. Now check the terminal is communicating with the PC-end RFbee, and then send the character ‘A’, ‘B’ or ‘C’. Note that the LED on the Arduino board will blink one, two or three times respectively – or five times if another character is received. It then reports back “Blinking completed!” to the host PC. For example (click to enlarge):
term2

Although that was a very simple demonstration, in doing so you can prove that your RFbees are working and can send and receive serial data. If you need more than basic data transmission, it would be wise to get a pair of RFbees to experiment with before committing to a project, to ensure you are confident they will solve your problem.

More Control

If you are looking to use your RFbees in a more detailed way than just sending data at 9600 bps at full power, you will need to  control and alter the parameters of your RFbees using the terminal software and simple AT-style commands. If you have not already done so, download and review the RFbee data sheet downloadable from the “Resources” section of this page. You can use the AT commands to easily change the data speed, power output (to reduce current draw), change the frequency, set transmission mode (one way or transceive) and more.

Reading and writing AT commands is simple, however at first you need to switch the RFbee into ‘command mode’ by sending +++ to it. (When sending +++ or AT commands, each must be followed with a carriage return (ASCII 13)). Then you can send commands or read parameter status. To send a command, just send AT then the command then the parameter. For example, to set the data rate (page ten of the data sheet) to 115200 bps, send ATBD3 and the RFbee will respond with OK.

You can again use the terminal software to easily send and receive the commands. To switch the RFbee from command mode back to normal data mode, use ATO0 (that’s AT then the letter O then zero) or power-cycle the RFbee.

RFbee as an Arduino-compatible board with inbuilt wireless

As mentioned previously the RFbee is based around an Atmel ATmega168 running at 8MHz with the Arduino bootloader. In other words, we have a tiny Arduino-compatible board in there to do our bidding. If you are unfamiliar with the Arduino system please see the tutorials listed here. However there are a couple of limitations to note – you will need an external USB-serial interface (as noted in Getting Started above), and not all the standard Arduino-type pins are available. Please review page four of the data sheet to see which RFbee pins match up to which Arduino pins.

If for some reason you just want to use your RFbee as an Arduino-compatible board, you can do so. However if you upload your own sketch you will lose the wireless capability. To restore your RFbee follow the instructions in Getting Started above.

The firmware that allows data transmission is also an Arduino sketch. So if you need to include RF operation in your sketch, first use a copy of the RFBee_v1_1.pde included in the repository – with all the included files. Then save this somewhere else under a different name, then work your code into the main sketch. To save you the effort you can download a fresh set of files which are used for our demonstration. But before moving forward, we need to learn about controlling data flow and device addresses…

Controlling data flow

As mentioned previously, each RFbee can have it’s own numerical address which falls between zero and 255. Giving each RFbee an address allows you to select which RFbee to exchange data with when there is more than two in the area. This is ideal for remote control and sensing applications, or to create a group of autonomous robots that can poll each other for status and so on.

To enable this method of communication in a simple form several things need to be done. First, you set the address of each RFbee with the AT command ATMAx (x=address). Then set each RFbee with ATOF2. This causes data transmitted to be formatted in a certain method – you send a byte which is the address of the transmitting RFbee, then another byte which is the address of the intended receipient RFbee, then follow with the data to send. Finally send command ATAC2 – which enables address checking between RFbees. Data is then sent using the command

Where data is … the data to send. You can send a single byte, or an array of bytes. length is the number of bytes you are sending. sourceAddress and destinationAddress are relevant to the RFbees being used – you set these addresses using the ATMAx described earlier in this section.

If you open the file rfbeewireless.pde in the download bundle, scroll to the end of the sketch which contains the following code:

This is a simple example of sending data out from the RFbee. The RFbee with this sketch (address 1) sends the array of bytes (testdata[]) to another RFbee with address 2.  You can disable address checking by a receiving RFbee with ATAC0 – then it will receive any data send by other RFbees.

To receive data use the following function:

The variable result will hold the incoming data, len is the number of bytes to expect, sourceAddress and destinationAddress are the source (transmitting RFbee) and destination addresses (receiving RFbee). rssi and lqi are the signal strength and link quality indicator – see the TI CC1101 datasheet for more information about these. By using more than two RFbees set with addresses you can selectively send and receive data between devices or control them remotely. Finally, please note that RFbees are still capable of sending and receiving data via the TX/RX pins as long as the sketch is not executing the sendTestData() loop.

I hope you found this introduction interesting and useful. The RFbees are an inexpensive and useful alternative to the popular Xbee modules and with the addition of the Arduino-compatible board certainly useful for portable devices, remote sensor applications or other data-gathering exercises.

For more information and product support, visit the Seeedstudio product pages.

RFbees are available from Seeedstudio and their network of distributors.

Disclaimer – RFbee products used in this article are promotional considerations made available by Seeedstudio.

In the meanwhile have fun and keep checking into tronixstuff.com. Why not follow things on twitterGoogle+, subscribe  for email updates or RSS using the links on the right-hand column? And join our friendly Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other –  and we can all learn something.

Posted in arduino, education, lesson, RF, rfbee, seeedstudio, tutorial, wireless, WLS126E1P, xbee

Review – Starman Electric Databridge Wireless I/O Modules

In this review we are going to have a look at some new wireless data modules that have just arrived on the market. They are the Databridge Wireless I/O modules from Starman Electric. Although there are many types of wireless modules out there, such as the discount 315 MHz units that are somewhat unreliable (well for me); and the great XBee series (as we used in Moving Forward with Arduino – Chapter Fourteen) – these Starman modules take it to the next level. How?

The concept of a databridge is a delightfully simple one. The two modules take the place of a wire. Digital, analogue, UART, even PC serial. No firmware settings to adjust, just plug them in and they work!

First of all, there are two physical types of unit, either DIP mount or SMD. The units below are the DIP version, 1mW output power:

topss1

The graph paper is 5mm square, and the module measures 53.85mm by 25.91mm. The DIP packaging (above) is meant for experimenters and prototypes, you can order SMD versions for production runs. There are also two power-output versions, 1mW with a theoretical range of 1km, and a 100 mW with a range of 4km. The higher power modules require the use of an external antenna. They require 3.3 volts DC, with a peak current draw of 37mA for the 1mW, and 120mA for the 100mW. For demonstration purposes I am using a Texas Instruments LP2950 to provide 3.3 volts DC at up to 100 mA.

Although the specification sheet is quite long (and you can download it from here) there are a few features that really stand out, including:

  • Automatic connection – a pair of modules will ‘lock’ onto each other without any extra work by the user;
  • A very high sampling rate of 200 samples per second with a latency of five millisconds;
  • Spread-spectrum radio operation – the modules will skip frequencies themselves for reliable connections;
  • You can have sixteen unique pairs working in the same area without cross-interference;
  • You can have two analogue channels and multiple digital channels simultaneously.

But enough talking, time to put them to the test. I will recreate some examples found in the Getting Started manual available for download here.

As I only have one pair of modules, and somehow I think my neighbours won’t be using any at this point in time, there is no need to set the pair’s unique network ID. However you do need to specify the master and slave in the module relationship (no switches…), which is done with pin 4 – to Vcc for master, and pin 4 to GND for slave. Now on with the show!

The first example of interest is number two in the guide – the wireless digital and analogue I/O bridge. To me this seems like an interesting wireless “repeater” to some Arduino analogue and digital outputs. Here is my test schematic used for the demonstrations in this review:

schematicss4

and my usual messy breadboards:
bboardss

Well this is a temporary test! The slave module board is running from a 9V PP3 battery so I can take it for a walk.

Anyhow, the setup is – four digital out lines from an Arduino, which are either high or low (+5v or GND). These are connected to pins ‘digital signal’ 1~4 on the master Databridge. Furthermore, Arduino analogue pin 1 went to the Databridge ‘analog signal’ pin 1. At the slave side of things, there are four LEDs with current limiting resistors connected to pins ‘digital signal’ 1~4; and two wires each from ‘analog signal’ 1 would be connected to a voltmeter. The digital output pins on slave modules default to ‘high’ unless driven otherwise.

Finally, there is also an LED and current limiting resistor coming from pin 32 of each unit – the ‘link’ pin. The link pin is a lifesaver. Here is a great feature – when the pair of units are within range of each other and matched as a pair, link goes high (3.3V). Out of range? It goes low (0V). Therefore you can test the range on these modules just by powering them up on a breadboard each, with the LEDs on pin 32, and go for a walk with a unit. When the LED is off – you’re out of range. And when you come back into range, the modules reconnect automatically.

Back to the test. First I just created a loop which turned the digital pins on and off, and the matching LEDs on the slave unit blinked on and off as expected. No extra code, no trying to create wacky functions to multiplex/demultiplex signals – this just works. The modules are like an invisible bunch of wires between two points. Never has anything wireless worked so easily for me.

Here is a quick video clip, first notice the lonely LEDs on each breadboard – the are the link LEDs. When I power cycle the master or slave, notice how quickly they reconnect. Please note that the slave unit retains the state of the digital outputs if connection is lost. So if a pin is high while connected – if the module loses radio contact, the pin will stay high.

The theoretical maximum working range is quoted as 1km for these 1mW modules. My indoor test allowed a distance of 11 metres, with three concrete walls of a thickness of ~110mm in between. Unfortunately living in my area I could not find a flat, open area large enough to test the maximum open-air range – however considering the indoor ‘concrete wall’ test and my experience with other wireless equipment of this power output, it would be accurate in an outdoor, line-of-sight application. As always, conduct your own real-life tests before making any project commitments  and so on.

And as always, I was curious about the current draw of the units while in use. The master module with the link LED on measured 53 milliamps, with the slave at the boundary of the radio range:

macurrss

The current use only dropped around 2 or 3 milliamps when the slave was next to the master. The slave module used 59 milliamps with the link LED on:

slcurrss

Therefore taking the LED current draw into consideration, the power usage of these modules is quite low considering the level of communication between them and the high sampling rate.

The next test was to see how the analogue data lines performed. According to example four in the Getting Started guide, the modules will reproduce an input of between 0 and 2.4 volts DC. So I have placed an 11k ohm resistor in series with a 10k ohm potentiometer with analog input 1, and measured the resulting output from the slave. Notice how I still have the digital data lines in use while using the analogue line.  Here is a short clip of this in action:

Amazing – a multitasking wireless module. Note that you could always use an op-amp to boost the output voltage back to the 0~5V DC range, an example of this is on page nine of the Getting Started guide.

Those above were but two from the many possibilities available when using these units:

  • wireless serial data links
  • remote on/off control of six items
  • robotics remote control
  • microcontroller I/O wireless extension…

Frankly – if you need to wirelessly connect more than one data line simultaneously, you have an excellent solution with the Databridge modules.

Update! – Radio licensing information:

These modules operate in the 2.4 GHz ISM (industrial, scientific and medical) band. For those in the USA, the Databridge is an FCC-approved “class B” device, and is only for use by OEM integrators (see page 16 of the datasheet.pdf). Starman Electric also state that the Databridge is certified for Canada and the EU (ETSI).

For those here in Australia, these units are operated under the conditions of the Radiocommunications (Low Interference Potential Devices) Class Licence 2000, and I feel are classed as “spread spectrum unit” under the preceding license.

Please conduct your own research with regards to radio transmitter licensing in your area. Furthermore, please read the tronixstuff “boring stuff” here.

But enough about that, where you can get them?

Australian customers can purchase these modules from our local distributor – Interworld Electronics; North Americans and the rest of the world directly via Starman Electric.

Remember, if you have any questions about these modules please contact Starman Electric via their website.

[Note – these wireless modules were loan units received from Starman Electric for review purposes]

Posted in databridge, part review, starman, wirelessComments (7)


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