| Item | Value | Description |
|---|---|---|
| Model | BHS140 | |
| Encoding | fixed, unidirectional | |
| Channels | 4 | |
| Frequency | 868.2MHz | |
| Modulation | On-Off-Keying (OOK) | |
| Symbol-Rate | 1 kHz | |
| Symbol-Encoding | Pulse-Width | |
| Antenna-Length (λ/4) | 86mm |
First step is to gather and analyze the data sent by the hand-held transmitter. Start rtl_sdr (or whatever tool you are using) and press a few buttons on the transmitter.
$ rtl_sdr -f 868000000 -s 2048000 sample.cu8
Found 1 device(s):
0: Realtek, RTL2838UHIDIR, SN: 00000001
Using device 0: Generic RTL2832U OEM
Found Rafael Micro R820T tuner
[R82XX] PLL not locked!
Sampling at 2048000 S/s.
Tuned to 868000000 Hz.
Tuner gain set to automatic.
Reading samples in async mode...
^CSignal caught, exiting!
User cancel, exiting...
Analyze the data with inspectrum: $ inspectrum sample.cu8
Each frame consists of a preamble and 32-bits of data (e.g. 0x02 0xEA 0xAB 0xBF):
| Symbol | Meaning | Comment |
|---|---|---|
very long Pulse followed by short gap |
Preamble | the first frame actually has a shorter preamble of 4667µs |
short pulse followed by long gap |
0 |
(duty factor < 0.5) |
long pulse followed by short gap |
1 |
(duty factor > 0.5) |
| Type | Timing |
|---|---|
very long |
5440µs |
long |
333µs |
short |
667µs |
Upon pressing the button on the hand-held, several frames are transmitted successively.
sniff.py- a command-line tool to read and decode hand-held transmitter data using my python RFM69-library on a Raspberry Pi.transmitter.py- a command-line tool to previously gathered codes via the RFM69-module.