Light Barrier Sensor

I am seeking a Light Barrier or any similar sensor, such as PIR to monitor if/when a vehicle passes certain points of an access road. Uplinks upon each event. Bidirectional detection would be appreciated, too. The distance to cover is supposed to be <10m. The road is not paved either, such that sunk-in sensors may not be eligible. Also radar-based systems must not be utilized, as the LoRaWAN infrastructure is located at an astronomical site with sensitive radio-telescopes around. We also require AU915 subband 2.

Any idea from the community?
Thanks, Ralf A.

Security system beam break detector - optical - will need some power but should be OK on solar.

Bi-directional, as in knowing which direction a vehicle went, will need two. It won’t be able to tell if two vehicles pass at the same time, so make it a pinch point.

PIR is based on radiated heat so not really great for anything other than warm bodies in ambient.

[Source: 20+ years doing bespoke security systems]

Thanks Nick, you rose a valid point. In the Chilean Atacama desert we are talking double digits of vehicles per day. Issue is the Bolivean gang of thieves at night snaffling scientific instrumentation …

They’d probably find it simpler to steal & sell the beam breaks, so make sure they are hidden.

The only other “easy” option is a ground loop detector which is easier to hide as long as no one sees it being installed.

any off-shelf solution known? Didn’t come across such.

In case you referred to those underground parking sensors - looking like a land mine - signal strength at the gateway may be mitigated owing to their locations

Ground loops are generally used at barriers - it’s that outline of a square of bitumen that you can see in the concrete - sometimes a box. But no, not the April Fool joke that is a LoRaWAN parking bay sensor.

Fundamentally it’s a metal detector loop - so the MCU, radio & antenna would be off to one side, presumably camouflaged to some extent.

Google “car loop detector” - in the UK I get many options, mostly in the £30 - £75 range with lots of options for the control box. Anyone with their own radio telescope should be able to MacGyver something easily enough, or even dare I say it, hack together the whole metal detector - Colpitts oscillator feeding pulses in to MCU …

i have see a project where they were detecting cell phone rssi (900hz-3.5ghz if memory serves me correctly) and bluetooth rssi (2.4ghz)

most thugs carry cell phones and these thing are permanently sending handshakes to the bts

but obviously something you will need to hack yourself together

Indeed, alternate RF signal detection (usually BT/BTLE &/or WiFi, but as you note sometimes also Cellular) is the basis of many a PaxCounter - often implemented in LoRaWAN enabled devices. Forum search is your friend if looking for examples. Note for others reading this also depending on jurasdiction longer term retention or use/disposal of captured signal data and identifying MAC/IMEI data may require careful handling under local privacy regulations - e.g. GDPR et al… not that that is often a problem with criminal gangs :wink:

Several years back a client had a similar problem (in that case with undesireables acessing a remote farm/buildings/live-stock down a remote narrow track), actually the client of a client. I conceived a system where (after the T-Leaves - Thieves! - sussed and even disabled and later stole! :man_shrugging: the active detectors initially tried (PIR/Ultrasonic Motion sensors, Light Gates, etc.), we implemented a couple of discrete speed bumps and monitored from vibration sensors (effectively mini earthquake sensors!) embedded in cast concrete at the side of the track so essentially hidden and tamper proof :-). The baddies couldn’t help but trigger on way in/out with any form of vehicle (could even pick up a mid sized motorbike if going at anything other than a slow walking pace). It was later ‘improved’ to add 3 vs initial 2 humps - with assymetric spacing to allow detection of direction. I heard later that similar, augmented systems were deployed in 2 way track traffic areas at the same farm site, and other sites where boundary/access security was a big concern, by my client. This was before LoRaWAN/TTN and used early LoRa P2P to get alarm/trigger data from monitor point(s) to control, but could be done just as easily with LoRaWAN today.

Genius - off to B&Q for a bag of cement mix …

I wonder if anyone has experience already with a Milesight Camera that is LoRaWAN capable and that can operate in “Line-Crossing” mode. Such it can detect bi-directional traffic. Caveat: it consumes a mere 10W and 16" with IR enabled.

How many can you afford to have go wrong due to being in a hostile environment and/or have stolen?

valid point given the price of ~800€ each, not mentioning the config effort…

The environment isn’t that hostile as you might anticipate. It’s supposed to be the driest place on earth, Only the air pressure is somewhat low with about 490 mbar and UV radiation is elevated, of course.

Temperature cycling between night & day?

yeap and wind gusts, we plainsmen need to wear oxygen hoses under our noses

Wind gusts are about securing the items properly, it’s insulating the electronics, power supply & batteries from regular temperature swings that just weren’t considered by the designers.

What is your overnight low & daytime direct sunshine high?

If you use Fuel Cells, they come with Oxygen storage so it should be OK to breath …

geographical latitude is about -22°

we got a Kerlink iStation at 5100m altitude (no issues at all), no external antenna, though, afraid of lightning strikes