Smart Badge

The Smart Badge, contains an IrDA transceiver, PIC microcontroller and an array of sensors. It periodically polls its sensors, transmits the result of the poll and then waits for commands from the location server. After a time-out period the Smart Badge goes to sleep. When it wakes up it repeats its loop.

If the Smart Badge is left still and in a dark place for a long time (e.g. your desk draw) then it will go into hibernation and will simply wake up and check to see if it has moved or if the lights have come up. If neither event happens it will go back to sleep without transmitting any data. Given that the IrDA interface consumes 1A peak, hibernation dramatically extends battery life.

Specifications

Processor	PIC16C74A-JW
Cycle period	2.3 sec
Data rate	38400 bps
Duty Cycle	1.7% (greater if beeps are generated)
Voltage	5V
Processor On current	1.56mA
Processor Sleep current	0.85mA
Size	54x86mm
Sensors	Tilt (4 in quadrature), light, sound, temperature, humidity
Actuators	Piezoelectric transducer (beeper)

Badge frame format

Frames are either output frames from the badge (called sensor frames), input frames to the badge from the location server (called command frames) or error frames generated by the badge in response to a command frame (called error frames). The badge is single buffered due to limitations in RAM space. A protocol field is used to distinguish between frame types as PROTO_DUMB and PROTO_SENSOR frames have exactly the same format. They differ only in the protocol field which is used to distinguish between Dumb Badge and Smart Badge devices. All frames contain a random field used to provide some variation in the data content (prior to encryption) of immobile badges, hence improving their resistance to cryptographic analysis.

All frames consists of a sync byte followed by 26 data bytes. Future versions will use IrDA framing. The IrDA framing may replace the sync and crc fields or may simply encapsulate the whole badge message in an IrDA message. The current proposal is to use two broadcast messages in the IrDA SIR protocol for badge-to-sensor communication:

SIR_UNITDATA.request(User-Data)
SIR_UNITDATA.indication(User-Data)

Of course the frame format is subject to change without notice. The next change is likely to be to increase the size of X, Y and Z to 32 bits each to provide positions to 10cm resolution. Although 28 bits would provide sufficient precision, unfortunately 28 bits isn't a convenient size, hence we will use 32 bits.

Sensor Frame

OUT_SYNC	outframe_data[0]
OUT_LENGTH	outframe_data[1]
OUT_RANDOM	outframe_data[2]
OUT_PROTOCOL	outframe_data[3]
OUT_SEQUENCE	outframe_data[4]
OUT_ADDRESS0	outframe_data[5]
OUT_ADDRESS1	outframe_data[6]
OUT_ADDRESS2	outframe_data[7]
OUT_ADDRESS3	outframe_data[8]
OUT_STATUS	outframe_data[9]
OUT_TEMPERATURE	outframe_data[10]
OUT_LIGHT	outframe_data[11]
OUT_HUMIDITY	outframe_data[12]
OUT_ROLL	outframe_data[13]
OUT_PITCH	outframe_data[14]
OUT_YAW	outframe_data[15]
OUT_X1	outframe_data[15]
OUT_X2	outframe_data[17]
OUT_X3	outframe_data[18]
OUT_Y1	outframe_data[19]
OUT_Y2	outframe_data[20]
OUT_Y3	outframe_data[21]
OUT_Z1	outframe_data[22]
OUT_Z2	outframe_data[23]
OUT_Z3	outframe_data[24]
OUT_SOUND	outframe_data[25]
OUT_CRC0	outframe_data[26]
OUT_CRC1	outframe_data[27]

Command Frame

IN_LENGTH	inframe_data[0]
IN_RANDOM	inframe_date[1]
IN_PROTOCOL	inframe_data[2]
IN_SEQUENCE	inframe_data[3]
IN_ADDRESS0	inframe_data[4]
IN_ADDRESS1	inframe_data[5]
IN_ADDRESS2	inframe_data[6]
IN_ADDRESS3	inframe_data[7]
IN_COMMAND	inframe_data[8]
IN_ARGUMENT_00	inframe_data[9]
IN_ARGUMENT_01	inframe_data[10]
IN_ARGUMENT_02	inframe_data[11]
IN_ARGUMENT_03	inframe_data[12]
IN_ARGUMENT_04	inframe_data[13]
IN_ARGUMENT_05	inframe_data[14]
IN_ARGUMENT_06	inframe_data[15]
IN_ARGUMENT_07	inframe_data[16]
IN_ARGUMENT_08	inframe_data[17]
IN_ARGUMENT_09	inframe_data[18]
IN_ARGUMENT_10	inframe_data[19]
IN_ARGUMENT_11	inframe_data[20]
IN_ARGUMENT_12	inframe_data[21]
IN_ARGUMENT_13	inframe_data[22]
IN_ARGUMENT_14	inframe_data[23]
IN_ARGUMENT_15	inframe_data[24]
IN_CRC0	inframe_data[25]
IN_CRC1	inframe_data[26]

Error Frame

OUT_SYNC	outframe_data[0]
OUT_LENGTH	outframe_data[1]
OUT_RANDOM	outframe_data[2]
OUT_PROTOCOL	outframe_data[3]
OUT_SEQUENCE	outframe_data[4]
OUT_ADDRESS0	outframe_data[5]
OUT_ADDRESS1	outframe_data[6]
OUT_ADDRESS2	outframe_data[7]
OUT_ADDRESS3	outframe_data[8]
ERRORED_FRAMES	outframe_data[9]
ERRORED_COMMANDS	outframe_data[10]
RESERVED	outframe_data[11]
RESERVED	outframe_data[12]
RESERVED	outframe_data[13]
RESERVED	outframe_data[14]
RESERVED	outframe_data[15]
RESERVED	outframe_data[15]
RESERVED	outframe_data[17]
RESERVED	outframe_data[18]
RESERVED	outframe_data[19]
RESERVED	outframe_data[20]
RESERVED	outframe_data[21]
RESERVED	outframe_data[22]
RESERVED	outframe_data[23]
RESERVED	outframe_data[24]
RESERVED	outframe_data[25]
OUT_CRC0	outframe_data[26]
OUT_CRC1	outframe_data[27]

Command Types

COMMAND_NULL	0x00
COMMAND_OUTFRAME	0x01
COMMAND_BEEP	0x02
COMMAND_ERRORS	0x03
COMMAND_ADDRESS	0x04
COMMAND_KEY	0x05

Protocol Field

PROTO_SENSOR	0
PROTO_COMMAND	1
PROTO_ERROR	2
PROTO_DUMB	3

Resources

The complete badge design (schematic, artwork) are available for download. At this time the badge control program is unavailable.

The original badge board and change list for version 1.

Contact

If you use the design or have any comments or suggestions we would like to hear from you.

H. W. Peter Beadle (Email: beadle@elec.uow.edu.au)

March 11, 1997

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