OpenStint Laptiming Decoder

OpenStint is a software defined radio (SDR) based laptiming decoder, using either HackRF One or RTL-SDR v4. It works both with its own transponder protocol and with AMB/RC3-based transponders. It can run on a Raspberry Pi 3 Model B+. Only a minimal electronics knowledge is required; touching a soldering iron is optional.

• 🎉 Supports OpenStint transponder, as well as RC3/RC4Hybrid/MRT and other RC3-clones
• 🔧 Off-the-shelf components, no electronic skills are required (HackRF One, RTL-SDR v3 & v4).
• 🏁 Tested with ZRound
• 📉 Low resource requirements: runs even on a Rapsberry Pi 3 Model B+
• ⏱️ Precise passing time detection (based on signal strength)
• 🚗 Passing speed detection (based on signal strength)
• 🧠 Adaptive filters enchance reception quality

Download: Windows users can download precompiled binaries; the rest of us have to compile from source.

Side-projects: openstint transponder | antenna preamplifier

Check out the track setup tutorial to get started. To learn more how SDR works, watch Andreas Spiess explaining it.

Compile from source

You have compile it from source. Install its dependencies first:

sudo apt-get install hackrf libhackrf libhackrf-dev librtlsdr-dev libliquid libliquid-dev libzmq3-dev cppzmq-dev libfec0 libfec-dev

Then checkout this repo, and build with cmake/make (Release build enables -O3 compiler flag, improves performance significantly):

cmake -DCMAKE_BUILD_TYPE=Release .
make
./src/openstint_hackrf   # or ./src/openstint_rtlsdr

Vehicle passings are printed to stdout and published with ZeroMQ at :5556. The easiest method for testing with real transponders is with a near-field magnetic probe (sub-$10 stuff, search on ebay/aliexpress or see Dave Jones DIY one).

To use goodies in the integrations/ directory, sudo apt-get install python3 python3-zmq as well.

Note on Mac: we can't brew install libfec, compile and install it from source.

If this is your first rodeo, sudo apt-get install cmake build-essentials libtool autoconf as well.

HackRF One users: there is a build flag SAMPLES_PER_SYMBOL, default to 4, resulting in 5 MSPS sampling rate. Better reception is achievable by setting it to 8 (10 MSPS) at the cost of higher CPU utilization. On resource-constrained environment, lower it to 2 (2.5 MSPS: lower CPU-usage, shittier reception). RTL-SDR maxes out at the required minimum of 2.5 MSPS (SAMPLES_PER_SYMBOL=2), there is no way to fine-tune that.

Integrations

The primary method of 3rd-party integration with OpenStint is via ZeroMQ. The openstint process listens by default on port :5556, and acts as a ZeroMQ PUBLISHER for arbitrary number of clients.

The decoder protocol is documented under the docs/ directory.

Find some built-in integrations in the integrations/ directory.

Command line arguments

HackRF

openstint_hackrf -h
Usage: openstint_hackrf [-d ser_nr] [-l <0..40>] [-v <0..62>] [-a] [-b] [-p tcp_port] [-m] [-t]
	-d ser_nr   default:first	serial number of the desired HackRF
	-l <0..40>  default:24  	LNA gain (rf signal amplifier; valid values: 0/8/16/24/32/40)
	-v <0..62>  default:20  	VGA gain (baseband signal amplifier, steps of 2)
	-a          default:off 	Enable preamp (+13 dB to input RF signal)
	-b          default:off 	Enable bias-tee (+3.3 V, 50 mA max)
	-p port     default:5556	ZeroMQ publisher port
	-m          default:off 	Enable monitor mode (print received frames to stdout)
	-t          default:off 	Use system clock as the timebase (beware of NTP jumps)

RTL-SDR

openstint_rtlsdr -h
Usage: openstint_rtlsdr [-d ser_nr] [-g <gain_dB>] [-D] [-b] [-p tcp_port] [-m] [-t]
	-d ser_nr   default:first	serial number of the desired RTL-SDR
	-g <dB>     default:20  	tuner gain in dB
	-b          default:off 	Enable bias-tee (+4.5 V)
	-p port     default:5556	ZeroMQ publisher port
	-m          default:off 	Enable monitor mode (print received frames to stdout)
	-t          default:off 	Use system clock as the timebase (beware of NTP jumps)

HackRF One or RTL-SDR?

Initial results show 2-3 dB better performace with a HackRF One when compared to an RTL-SDR v4. Given the ~40 dB effective dynamic range of these devices, this is not noticable in practice (if it is, re-think the antenna setup). A HackRF One clone costs 3x more as an RTL-SDR v4 dongle; an original from Great Scott Gadgets is 6-8x more expensive.

For permanent setups, prefer the HackRF One though. The RTL-SDR dongle heats up considerably. I would not put it into an enclosed electrical box, and I would not leave it exposed to sunshine neither. The HackRF board is much less dense, thermal management is not a problem there.

Radio	Typ. price	Est. dynamic range	Thermal	Default gain	LSB Sensitivity	Notes
RTL-SDR v3	$35	40 dB	OK	no gain control	2 uVpp (-110 dBm)	a bit noisy
RTL-SDR v4	$40	37 dB	warm	gain:20.7	8 uVpp (-98 dBm)	in-band images!
HackRF One	$120	39 dB	OK	PA:off LNA:24, VGA:20	17 uVpp (-91 dBm)	-

Contribution

Submit PRs according to the project's core values:

• it should be and remain a solution for small-scale clubs and friendly gatherings
• it should run on constrained hardware (Raspberry Pi 3 Model B+)
• the interfaces should be simple and well documented (to promote 3rd-party integration)
• "does one thing and one thing well" phylosophy

Otherwise, I'll to adhere myself to the C4 community process.