Table of Contents
Overview
openbeacon readers dump one RF channel/MAC and send them via UDP packets to a central server.
Original
Original OpenBeacon Readers are nice little black boxes created by milosch with two nRF24L01 and two antenna. (i.e. two receivers in nearly the same position). Problem is: they are expensive, and we currently don't have any.
Replacement
We sometimes use r0kets as readers. Their sensitivity is worse and they are very directional, but it's good enough to play around with it.
Current version
bridge firmware flashed on r0ket, packet dump read via USB serial and sent on with a small script.
- e.g. beacon-udp.pl
- or a compiled version of obreader.c if perl is too slow
packet format
The OpenBeacon packets are 16 byte long. The reader prepends a 16-Byte header before it sends it off to the central server.
NOTE: all fields are in “network order” i.e. big endian.
The header looks like this:
| byte | name | description |
| 0x00 | icrc | ccitt16(bytes[0x2:end]) XORd with 0xffff |
| 0x01 | ||
| 0x02 | proto | BEACONLOG_SIGHTING == 1 |
| 0x03 | interface | 0 or 1 on official reader, 0 always in our code |
| 0x04 | readerid | needs to be added to src/bmReaderPositions.h |
| 0x05 | ||
| 0x06 | size | size of the whole packet (usually 32) |
| 0x07 | ||
| 0x08 | ctr | sequence number over all packets |
| 0x09 | ||
| 0x0a | ||
| 0x0b | ||
| 0x0c | time | timestamp in seconds (milosch: since bootup, we: unix time_t) |
| 0x0d | ||
| 0x0e | ||
| 0x0f |
this is followed by the raw packet as captured by the rf interface.
For the reference, the openbeacon packet format looks like this:
NOTE: we use what milosch calls RFBPROTO_BEACONTRACKER_OLD2 because that's what sputnik and HOPE/AMD used.
| byte | name | description |
| 0x00 | len | length of the packet (usually 16) |
| 0x01 | type | openbeacon (0x17) |
| 0x02 | button | sputnik “button” press. R0ket=0xff which makes openbeacon-tracker output “button=true” |
| 0x03 | strength | 0x00 / 0x55 / 0xaa / 0xff (low to high) rf sending strength used |
| 0x04 | idx | monotonically increading sequence. Original sputnik dies after 0xffffffff |
| 0x05 | ||
| 0x06 | ||
| 0x07 | ||
| 0x08 | beacon | openbeacon id |
| 0x09 | ||
| 0x0a | ||
| 0x0b | ||
| 0x0c | unused | unused fields. r0ket = 0xff 0xff |
| 0x0d | ||
| 0x0e | crc | ccitt16(bytes[0x0-0xd]) |
| 0x0f |
We added a new packet types to transmit the nickname:
| byte | name | description |
| 0x00 | len | length of the packet (usually 16) |
| 0x01 | type | 0x23 / 0x24 / 0x25 |
| 0x02 | beacon | openbeacon id |
| 0x03 | ||
| 0x04 | ||
| 0x05 | ||
| 0x06 | string | up to 8 ascii characters, 0-terminated if less |
| … | ||
| 0x0d | ||
| 0x0e | crc | ccitt16(bytes[0x0-0xd]) |
| 0x0f |
if (length(nickname)<=8): Packet 0x23 is sent with the nickname else Packet 0x24 is sent with nickname[0:7] Packet 0x25 is sent with nickname[8:15] # longer nicknames get truncated. fi
Our reader implementation also send a heartbeat packet every second. This packet has the standard reader header, but the last 16 bytes are just:
| byte | name | description |
| 0x00 | type | RFBPROTO_READER_ANNOUNCE (22) |
| 0x01 | unused | 0x0 |
| … | ||
| 0x0d | ||
| 0x0e | crc | ccitt16(bytes[0x0-0xd]) |
| 0x0f |