One
RF technology B868 Tiny Radio Module ( Tiny 112 )
Introduction
This is a review of the One RF
technology B868 Tiny Radio Module, which is an FM radio MODEM. It is
a half duplex FSK transceiver operating in the license free 868MHz
ISM band. Also described are simple RF MODEM designs for connecting
to an RS232 port and to a PC USB interface.
Description
What you get is a module which is
approx 32 x 19mm, with a integrated antenna covering the board
circuitry.
Around
three of the module edges are gold flashed connections to the
internal circuitry. The module is designed to sit into a cutout of a
PCB, although for breadboarding (accepting limited RF performance) it
can just be wired to.
The module has a TTL level RS232
protocol interface through which data or AT commands may be passed.
The module has additional pins, four of which can be configured as
digital IO and two which are Analog to digital convector inputs.
Power requirements are modest, a total
of 36mA at between 3V and 5.25V being required, through two filtered
power pins. This falls to 4mA when the RF link is not active, and to
0.4mA when the module is in hardware standby.
The modules have several modes of
operation, which are accessed through the AT command set. Modes are
as follows:
Normal
where data arriving at the module RX pin is transferred to another modules TX pin
Secure
this mode is like normal mode expect
that the data is packeted up and and gets acknowledged by the
receiving device. This gives more data security.
Addressed
this allows the setting up of networks
of modules. Each module is given a network number ( 0- 65535 ), which
allows it to communicate with other modules with the same network
number. Then within a network each module is given a unique ID(
0-255). Then data can be routed to a specific module by adding the
module ID as a prefix. e.g. “002= fred” will send “fred”
to module 002. Received messages have the source appended to the
message. e.g. “004=fred” is a message from module 004.
Note that here the datasheet is wrong
as it implies that the message is terminated by a <CR>. In
reality the message is terminated by a programmable timeout accessed
through the AT command set.
IO Copy
this mode allows the state of the IO
pins to be sent from a master module to a slave module.
Techie features
Well the datasheet
has all the info, but a few of the headline facts.
Range - LOS upto 300m.
For best operating range a PCB with
ground plane is recommended. Data rate - 10kbits-1 Frequency - 868MHz
Things to be aware of
Not many actually, it does what it says it does, in the main.
Data sheet is inaccurate about message termination in address
modes. It is a time out, not a character which terminates a message.
This can have implications for throughput in this mode.
Getting into AT mode requires the use of some software as my hand
cannot type the +++ sequence fast enough. I have used Teraterm
with a simple script to do this.
Conclusions
A top notch piece of kit, easy and quick to get operational. If
you want an RF link for project and can't be bother with all the fuss
of doing it yourself this is the way to go.
Design
Ideas
PC RS232 RF MODEM
By adding a regulator, a Max232 RS232 level shifter and a few
discrete components a simple RS232 to RF MODEM adapter can be made.
See circuits below.
The PSU needs to be 6V with a current
rating of least 200mA.
See here to purchase a PCB or kit of parts for the project.
PC USB to RF MODEM
Using the FTDI FT232BM USB chip a
simple USB to RF MODEM can be designed. See circuits below.
FTDI drivers ( here
) for the device provide either a virtual COM port interface or an
API DLL for coding with VB, VC, Delphi etc. Drivers are available for
a wide range of operating systems, including all the usual suspects.
See here to purchase a suitable PCB or
kit of parts for the project.
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