BiM-418, -433 MHz Transceiver

BiM Specs

Please Note:

All North American purchases of Radiometrix BiM products must be made through Lemos International by filling the Request Quote form.

BiM-418, -433 MHz Transceiver
The BiM-418-40 and BiM-433-40 are miniature UHF radio modules capable of half duplex data transmission at speeds up to 40 kbit/s over distances of 30 meters "in-building" and 120 meters open ground.

The BiM-418-40 Transceiver Module	Request Quote

Typical applications Pin Description A test circuit Performance data Antenna requirements Type Approval BIM-UHF Transceiver Applications Note Sending and Receiving Digital data Direct Digital, TXD > RXD at 5 Volt CMOS Levels RS232" Serial data Linear operation Digitized analogue data Packet data Networks Receiver Battery Saving Interface logic Signal Propagation PCB Layout and design notes

UK Version - BiM-418-40 Euro Version - BiM-433-40 Typical features include: Miniature PCB Mounting module SAW controlled FM transmission at -6dBm ERP. License Exempt operation in UK on 418MHz, MPT 1340 (BiM-418-40) ETS 300-220 tested for European use on 433.92 MHz (BiM-433-40) SAW controlled FM transmission at -6dBm ERP. Double conversion Superhet receiver -107dBm receive sensitivity Single 4.5 to 5.5 Volt supply < 15mA (tx or rx) Half duplex data at up to 40 kbit/s Reliable 30 meter in-building range Direct interface to 5V CMOS logic On board data slicer, supply switches and antenna change over. Fast 1ms power up enable for duty cycle power saving The module integrates a low power UHF FM transmitter and matching superhet receiver together with the data recovery and TX/RX change over circuits to provide a low cost solution to implementing a Bi-directional short range radio data link. The high data rates (up to 40kbit/s) and fast TX/RX changeover ( <1ms ) make the BiM transceiver ideal for high integrity one to one links / multi-node packet switch networks. Rapid RX power up ( <1ms ) allows effective duty cycle power saving of the receiver for battery powered applications (eg. 15µA average @ 1ms ON : 1sec OFF).

Typical applications include:-
Medium speed computer networks
Laptop > PC > printer links
High integrity wire free Fire / Security alarms Building environment control / monitoring Vehicle alarm systems Remote meter reading Authorization / Access control

Block diagram

Mechanism dimensions

Pin description:

pin 1 & 3	RF GND	These pins should be connected to the ground plane against which the integral antenna radiates . Internally connected to pins 9,10,18 .
pin 2	Antenna	RF input / RF output for connection to an integral antenna. It has a nominal RF impedance of 50W and is capacitively isolated from the internal circuit.
pin 9,10,18	Vss	0 volt connection for the modulation and supply.
Pin 11	CD	Carrier Detect - When the receiver is enabled, a low indicates a signal above the detection threshold is being received. The output is high impedance (50kW) and should only be used to drive a CMOS logic input.
Pin 12	RXD	This digital output from the internal data slicer is a squared version of the signal on pin 13 (AF). This signal is used to drive external digital decoders, it is true data (i.e. as fed to the transmitters data input). The 10kW output impedance is suitable for driving CMOS logic. Note: this output contain squared noise when no signal is being received
pin 13	RX Audio	This is the FM demodulator output .It has a standing DC bias of approximately 1.5Volts and may be used to drive analogue data decoders such as modems or DTMF decoders. Output impedance is 10KOhm. Signal level approx. 0.4V pk to pk. We recommend this signal always be available on a convenient test point for diagnostic purposes. Note: unlike the RXD output which is always true data, this output is true data on the BIM-418 and inverted on the BIM-433
pin 14	TXD	Should be driven directly by a CMOS logic device running on the same supply voltage as the module. Analogue drive may be used but must not drive this input above Vcc or below 0V. This input should be held at <0.5V when the TX is not selected to prevent current leak (see block diagram).
pin 15	TX select	Active low transmit / receive selects with 10kW internal.
Pin 16	RX select	pull-ups. They may be driven by open collector or CMOS logic

All states are valid

Pin 15 TX	Pin 16 RX	Function
1 1 0 0	1 0 1 0	power down (<1µA) receiver enable transmitter enable self test loop back
Note - loop test is at reduced TX poxer
pin 17	Vcc	positive supply, supply voltages from +4.5V to +5.5V may be used. Reverse polarity will destroy the module. Supply is internally decoupled. Maximum ripple content 50mV pk to pk.

Test circuit BIM-UHF

Warning: Don't be tempted to adjust the trimmer on the module, it controls the receive frequency and can only be correctly setup with an accurate RF signal generator.

Performance Data
ambient temperature: 20 °C
supply voltage: +5.0V, unless noted otherwise
Data applies to all frequency versions, except where noted

Parameter
DC parameters		Min	Typ	Max	Units	Notes
Operating supply range, Vcc		4.5	-	5.5	V	-
Supply current Transmit (-F version)		8	12	15	mA	-
Transmit (-HP version)		15	17	21	ma	-
receive		10	12	16	ma	-
loop test		-	20	25	ma	-
standby		-	-	1	µA

Parameter		Min	Typ	Max	Units
RF Parameters - Transmit
Radiated power (ERP) (-F version)		-10	-6	-3	dBm	1
(-HB version)		+3	+6	+10	dBm	1
Transmit frequency (Frf) BiM-418-40		-	418.000	-	MHz	-
Transmit frequency (Frf) BiM-433-40			433.920	-	MHz	-
Initial frequency accuracy		-75	0	+75	kHz	-
Overall frequency accuracy		-95	0	+95	kHz	-
Spurious radiation			meets	ETS	300-	220
FM deviation (+/-)		15	20	30	kHz	2
Distortion		-	5	10	%	3
Modulation response @ -3dB		DC	-	32	kHz	-

Parameter		Min	Typ	Max	Units	Notes
RF Parameters - Receive
Receive frequency (Frf) BiM-418-40		-	418.000	-	MHz	-
Receive frequency (Frf) BiM-433-40		-	433.920	-	MHz	-
Receiver sensitivity		-100	-107	-	dBm	-
		0.1	-	22	kHz	-
AF output level, pin 13, pk to pk		-	400	-	mV	-
Local Oscillator leakage, pin 2		-	-57	-	dBm	-
IF Bandwidth		-	200	-	kHz	-
AFC lock range (5µV signal)		-	200	-	kHz	-

Parameter		Min	Typ	Max	Units	Notes
Timing
RX select low to valid CD		-	-	1	ms	-
RX select low to valid RXD		-	-	3	ms	-
Transmit to Receive delay		-	-	1	ms	-
RF input (5µV) to valid CD		-	-	0.5	ms	-
RF input (5µV) to stable AF		-	-	0.5	ms	-

Parameter		Min	Typ	Max	Units	Notes
Base Band transfer function
(through a pair of transceivers) Linear drive (4V pk to pk, sine)
AF response @ -3dB		0.1	-	17	kHz	-
Analogue distortion		-	5	10	%	-

Parameter		Min	Typ	Max	Units	Notes
Digital drive
Data rate ( 50:50 )		-	-	40	kbits/s	4
Time between transitions		25	-	2000	µs	5
Average Mark:Space ratio		30	50	70	%	6
preamble duration (10101010)		3	-	-	ms	-
data delay (TXD to RXD)		-	25	-	µs	-

Parameter		Min	Typ	Max	Units	Notes
Interface levels	- inputs
TX & RX select,	Vhigh	Vcc-0.5	-	Vcc	V	-
	Vlow	0		1	V	-
Source current	@Vlow=0	0.5		1	ma	-
TXD	Vhigh	0Vcc-0.5		Vcc	V	-
	Vlow	o		0.5	V	-

Parameter		Min	Typ	Max	Units	Notes
Interface levels - outputs	V high		Vcc-0.6	Vcc	V	-
(no load)	V low		0.2	1	V	-

Notes:
1. module on 50mm square ground plane , 16cm whip antenna
2. Standard modulation : 2kHz square wave, 0 to Vcc
3. 1kHz, 4V pk to pk, Sinewave centered on +2.5V at pin 14 (TXD)
4. Digital drive, 50:50 mark:space (over 4ms) data pattern.
5. High or Low pulse.
6. Averaged over any 4ms period

Absolute maximum ratings
Supply voltage Vcc, pin 17	-0.1	to	+6V
All input / output pins	-0.1	to	Vcc + 0.1 V
Operating temperature	-20°C	to	+55°C
Storage temperature	-40°C	to	+100°C

Signal to noise curve

Timing waveform

A	Helical	Wire coil, connected directly to pin 2, open circuit at other end. This antenna is very efficient given it's small size (20mm x 4mm dia.). The helical is a high Q antenna, trim the wire length or expand the coil for optimum results. The helical de-tunes badly with proximity to other conductive objects.
B	Loop	A loop of PCB track tuned by a fixed or variable capacitor to ground at the 'hot' end and fed from pin 2 at a point 20% from the ground end. Loops have high immunity to proximity de-tuning.
C	Whip	This is a wire, rod, PCB track or combination connected directly to pin 2 of the module. Optimum total length is 17cm (1/4 wave @418MHz). Keep the open circuit (hot) end well away from metal components to prevent serious de-tuning. Whips are ground plane sensitive and will benefit from internal 1/4 wave earthed radial(s) if the product is small and plastic cased.

Antenna configuration

Antenna selection chart

	A	B	C
	helical	loop	whip
Ultimate performance	**	*	***
Easy of design setup	**	*	***
Size	***	**	*
Immunityproximinty effects	**	***	*
Range open ground to similar antenna	80m	50m	120m

The antenna choice and position directly controls the system range. Keep it clear of other metal in the system, particularly the 'hot' end. The best position by far, is sticking out the top of the product. This is often not desirable for practical/ergonomic reasons thus a compromise may need to be reached. If an internal antenna must be used try to keep it away from other metal components, particularly large ones like transformers, batteries and PCB tracks/earth plane. The space around the antenna is as important as the antenna itself.

Type approval

The BiM-418-40 is type approved in the UK to MPT1340 for use in Telemetry, Telecommand and In-Building alarm applications.

CONFORMANCE to MPT1340 REQUIRES THAT:

1. The transmitting antenna must be one of the 3 variants given in the data sheet. Antenna structures which yield ERP gain are not permitted.
2. The module must be directly and permanently connected to the transmitting antenna without the use of an external feeder. Increasing the RF power level by any means is not permitted. 3. 3. The module must not be modified nor used outside it's specification limits.
4. The module may only be used to send digital or digitized data.Speech / Music are not permitted.
5. The equipment in which the module is used must carry an inspection mark located on the outside of the equipment and be clearly visible. The minimum dimensions of the inspection mark shall be 10 x 15 mm and the letter and figure must be no less than 2mm. The wording shall read: " MPT 1340 W.T. LICENSE EXEMPT ".
6. Products intended for UK commercial application must be notified to the Radiocommunications Agency (RA) on form RA 249 ( Cat I), obtainable from the
RA's library service, Tel 0171 211 0502/ 0505

OEM Manufacturers incorporating the BiM-418-40 transceiver as a component part of their product are authorized by Radiometrix Ltd to quote our type-approval provided all the above conditions are met.

MPT 1340 is the type approval specification issued by the RA and may be obtained from the RA's library service on 0171 211 0502/ 0505.

BIM-UHF Transceiver Applications Note

Sending and Receiving Digital data

The BIM contains no data coding or decoding functions. These must be provided by the external controller, usually a single chip microprocessor, e.g. Arizona Microsystems PIC, Motorola MC68HC05 or similar. Alternatively a dedicated protocol controller such as CML's FX909 or Echelon's Network chips will work well.

The Radiometrix RPC-000-A Radio Packet Controller IC provides all the processor intensive low-level packet formatting and data recovery functions required in a high speed bi-directional data link/network. The RPC-418-A and RPC-433-A provide a self-contained UHF radio port for a host micro controller. The board combines a BIM transceiver and a RPC packet controller. (Data available on request.)

A pair of BIM transceiver's will transmit direct serial data applied to the TXD input and reproduce direct serial data at the RXD output of receiving BIM The BIM may also be used with linear data e.g. from modem IC's (see test circuit for linear biasing of TXD input).

Typical microcontroller interface

Direct Digital, TXD > RXD at 5V CMOS Levels

The data path through a pair of BiM's is AC coupled. This places 3 basic constraints that any serial code must satisfy for reliable transfer.

1. Pulse width time The receiver base band bandwidth and the AC coupling determines that the time, T, between any 2 consecutive transitions in the serial code must satisfy: 25µs < T < 2ms

2. RX settling time The AFC and data slicer in the receiver require at least 3ms of '10101010' preamble to be transmitted before the data at the RXD output may be considered reliable. Increasing this time to 5ms will give increased immunity to RF interference.

3. Mark:Space ratio The data slicer in the receiver is optimized for data waveforms with 50:50 Mark:Space averaged over any 4ms period. The slicer will tolerate sustained asymmetry up to 30/70 (either way), however, this will result in up to increased in pulse width distortion and a decreased noise tolerance.

Any serial data waveform satisfying the above criteria will pass reliably through a pair of BIM's

Fully buffered CMOS interface - digital drive

"RS232" Serial data

It is possible to transmit "RS232" serial data directly at 4.8 to 38.4kbps baud between a pair of BIM transceivers in half duplex. The data must be "packetised" with no gaps between bytes. i.e. :

The data must be preceded by >3ms of preamble (55h or AAh) to allow the data slicer in the BIM to settle, followed by 1 or 2 FFh bytes to allow the receive UART to lock, followed by a unique start of message byte, (01h), then the data bytes and finally terminated by a CRC or check sum. The receiver data slicer provides the best bit error rate performance on codes with a 50:50 mark:space average over a 4ms period, a string of FFh or 00h is a very asymmetric code and will give poor error rates where reception is marginal. Only 50:50 codes may be used at data rates above 20kbit/s.

We recommend 3 methods of improving mark:space ratio of serial codes, all 3 coding methods are suitable for transmission at 40kbit/s :-

Method 1 - Bit coding

Bit rate , Max 40kbits/s , Min 250bit/s Redundancy (per bit) 100% (Bi-phase), 200% (1/3 : 2/3)

Each bit to be sent is divided in half, the first half is the bit to be sent and the second half, it's compliment. Thus each bit has a guaranteed transition in the center and a mark:space of 50:50 . This is BI-phase or Manchester coding and gives good results, however the 100% redundancy will give a true throughput of 20kbit/s.

A less efficient, variation of BI-phase is 1/3 : 2/3 bit coding. Each bit to be sent is divided into 3 parts, the first 1/3 is a low, mid 1/3 is the data bit and final 1/3 is high. This code is easy to decode since each bit always starts with a negative transition. This code should not be sent faster than 100µs per bit (10kbit/s) since the mark/space can vary for 33 to 67%.

Method 2 - Byte coding

Bitrate, Max 40kbit/s , Min 2kbit/s Redundancy (per byte) 25% (synchronous), 50% (async)

If only a subset of the ASCII code is required (e.g. 0-9 , A-Z and a few control codes) then translate (via. a look up table) the required ASCII codes into the 8 bit codes below. These codes all have a 50:50 mark:space when sent serially.

Of the 256 possible 8 bit codes, 70 contain 4 ones & 4 zeros. The 68 Hex codes below have a 50:50 mark:space and may either be sent/received from a standard serial port (UART) using 1 start, 1 stop and no parity or as bytes of a synchronous code. Use for this subset also allows simple byte error checking on reception as all received codes must contain exactly 4 one's and 4 zero's.

(note 0F & F0 have been omitted to minimize consecutive 0 or 1's)

Other subsets are also possible e.g. a 10bit code has 1024 differs, 252 of which have 5 one's and 5 zero's i.e. a 50:50 M:S ratio.

Method 3 - FEC coding

Bit rate , Max 40kbit/s , Min 4.8kbit/s Redundancy (per byte) 100%

Each byte is sent twice; true then it's logical compliment. e.g. even bytes are true and odd bytes are inverted. This preserves a 50:50 balance.

A refinement of this simple balancing method is to increase the stagger between the true and the inverted data streams and add parity to each byte. Thus the decoder may determine the integrity of each even byte received and on a parity failure select the subsequent inverted odd byte. The greater the stagger the higher the immunity to isolated burst errors.

Linear operation

A pair of transceivers may also be viewed as a linear analogue channel with a pass baseband of 100Hz to 17kHz with <10% distortion. The ultimate S/N ratio being >40dB
(see quieting curves v RF input). The test circuit shows the TXD input biased for linear operation and a simple digital filter to shape the transmit data to a raised-cosine wave shape. The 22kW resistor linear- biases the TXD input. The drive voltage should be between 3.5 and 5V pk to pk to achieve full modulation (greatest S/N at receiver)

Linear drive

Raised-cosine shaping may be applied externally to any serial data stream and will yield better error performance than unshaped data at high data rates (up to 40kbit/s) for data steams with 50:50 mark:space (4ms averaging period). Several excellent modem chips
(FX 589 & FX 909) are available for Consumer Microcircuits Ltd (CML tel +44 (0)1376 513833). These chips employ GMSK (shaped data and matched receive filters) and enable operation up to 40kbit/s.

Raised cousine generator

Digitized analogue data

Linear operation of BIM transceivers will allow direct transfer of analogue data, however in many applications the distortion and low frequency roll off are too high (e.g. bio-medical data such as ECG). The use of delta modulation is an excellent solution for analogue data in the range 1Hz up to 4kHz with less than 1% distortion. A number of propitiatory IC's such as Motorola's MC3517/8 provide CVSD Delta mod/demod on a single chip.

Where the signal bandwidth extends down to DC , such as strain gauges, level sensing, load cells etc. then V-F / F-V chips (such as Nat Semi LM331) provide a simple means of digitizing.

Packet data

In general, data to be sent via a radio link is formed into a serial "packet" of the form :-

Preamble - Control - Address - Data - CRC

Where:

Preamble:
Control:	This is mandatory for the receiver in the BIM to stabilize. The BIM will be stable after 3ms. Additional preamble time may be desired for decoder bit sync., Software carrier detection or receiver wake up.
Address:	This information is used for identification purposes and would at least contain a 16/24 bit source address, additionally - destination address, site / system code , unit number and repeater address's may be placed here.
Data:	User data , generally limited to 256 bytes of less (very long packets should be avoided to minimize repeat overheads on CRC failure and channel hogging).
CRC:	16/24 Bit CRC or Checksum of control-address-data fields used by the decoder to verify the integrity of the packet

The exact makeup of the packet depends upon the system requirements and may involve some complex air-traffic density statistics to optimize through-put in large networked systems.

Networks

BIM's may be used in many different configurations from simple pair's to multi-node random access networks. The BIM is a single frequency device thus in a multi node system the signaling protocol must use Time Division Multiple Access. In a TDMA network only one transmitter may be on at a time, "clash" occurs when two or more transmitters are on at the same time and will often cause data loss at the receivers. TDMA networks may be configured in several ways - Synchronous (time slots), Polling (master-slave) or Random access (async packet switching e.g. X25). Networked BIM's allow several techniques for range / reliability enhancement:

Store and forward Repeaters:

If the operating protocol of the network is designed to allow data path control then data may be routed "via" intermediate nodes. The inclusion of a repeating function in the network protocol either via dedicated repeater/router nodes or simply utilizing existing nodes allows limitless network expansion.

Spacial Diversity:

In buildings multi-path signals create null spots in the coverage pattern as a result of signal cancellation. In master-slave networks it is cost effective to provide 2 BIM's with separate antenna at the master station. The null spot patterns will be different for the two BIM's . This technique 'fills in' the null spots, i.e. a handshake failure on the first BIM due to a signal null is likely to succeed on the 2nd BIM

Receiver Battery Saving

In many applications the receiver need not be always waiting for a signal (i.e. drawing 15mA). Often it is only required to turn the RX on after a transmission to receive handshake data, thereafter it may be deselected (i.e. <1mA leakage current).

In applications where a receiver needs to respond to a call, duty cycle power saving is very effective. For example selecting the receiver 3 times a second for 1ms and sampling the CD output for the presence of a signal will give an average current drain of < 50µA. In this example a 700ms preamble "wake up" would be used.

Interface logic

The logic control / data lines in and out of the BIM all have 10kW series EMC isolation resistors internal to the BIM (see BIM block diagram). We recommend that RXD and CD outputs be used only to drive CMOS logic inputs and no more than 5 cm of PCB track. Care should also be taken in the routing of the RXD , TXD , CD & AF tracking to minimize the cross talk between these high impedance lines. In some applications it is desirable to mute the continuous noise output on the RXD line when no signal is present, simple CMOS logic gating with the CD signal may be desirable.

There is a dc path of 20 kW from the TXD input to the internal switched TX supply. (see block diagram), it is desirable to hold TXD low whilst TX select is high (i.e. when not transmitting data).

The CD output is designed to be fast acting (< 1 ms), and can under conditions of weak signal or interference exhibit fast spurious pulses. It can be beneficial to drive a Schmitt trigger CMOS gate with this output and to include an additional R-C time constant between the CD output and the Schmitt input gate. The R should be 100 kW or greater and the additional time constant delay must be allowed for in the control software (i.e. preamble times etc.).

Signal Propagation

Three predominant effects are observed in the propagation of short range VHF / UHF signals in and around obstacles :-

1. Signal reflection:
This gives rise to multiple paths between the transmitter and the receiver. Since these paths will be of different lengths, the arriving signals will have differing phases and strengths leading to signal cancellation at specific points in space. I.e. null points are observed. These nulls are physically small i.e. moving either the transmitter or receiver a few centimeters will be enough to take the signal out of the null. They are more frequent in situations of weak signal and where lots of large metal items are present, they are totally absent in open ground situations.

2. Signal shadowing:
This occurs behind large sheets of metal e.g. trucks, foil backed plasterboard, steel reinforced floors, etc. In such areas, signals are received predominantly by reflection from other objects. The shadow areas are of similar dimensions to the shielding object and show as areas of weaker average signal level with an increased occurrence of nulls due to multipath (see 1. above).

3. Signal absorption:
Principally observed when signals pass through thick damp stone walls, the effects are similar to 2. above but there is less reflected signal.

PCB Layout and design notes:

Leave 1mm all round module (i.e. PCB footprint area of 25x35mm)
PCB holes - 1.2mm or socket strips
Keep AF track away from RXD & TXD - to avoid cross talk.
Put a test point on the AF pin for simple radio checking with a scope.
Ground plane all unused PCB area around and under module.
Position module and antenna as far from high speed logic and SMPS as possible Microprocessors with external data/address busses ALWAYS cause interference.
Provide LED status lights on TX, RX & CD (direct or by plug on test PCB)
For complex networks - provide software test routines for :-continuous RX, continuous TX, loop test, Simple master / slave "ping-pong".
The BIM-can (fig. 11) is available and may be used for shielding to achieve an optimal radio performance

BIM - can layout

Hole pattern BIM-UHF + BIM-can Click

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