Detecting vehicles in one direction only. How to do it?

Mark42 · May 3, 2019

I need to sense the arrival of vehicles along a driveway, to switch on security lighting at night. But only to operate when vehicles arrive, not when they are leaving and driving away.

I bought a USVD-4X ultrasonic detector:
Vehicle Detector | Drive Through Sensing - https://www.motion29.com/products/controlandsensing/drivethruvehiclesensorusvd4x/default.htm
I assumed the 'pulse on entry' and 'pulse on exit' settings determined the direction of travel of the vehicle (ie entry to, or exit from, a premises). But tests show otherwise: it means pulse on arrival and stopping by the sensor, and/or another pulse on driving away, like at a drive-through food place.

Is there any off-the-shelf device which will do what I need, without having say two PIRs or break-beams, then complicated logic in a microcontroller which will probably need rebooting or will otherwise go wrong. I want a fit-and forget industrial quality solution.

Any ideas?

Thanks, Mark

marconi · May 4, 2019

Re#14 - Good man. We love pictures of installations, especially if done well.

Mark42 · May 5, 2019

Andy Wilko said:
Herkules unit ... have to make sure you mount it on a firm surface and at least 3 meters from the ground. ...

One concern: this is on the drive to a listed building where ugly poles aren't really appropriate. Is it acceptable to mount the Herkules 600mm up from the ground on a granite post and it still work? Can be angled upwards if needed.

There is one existing power post I could use, but this has 3 x 12kV cables on one side which supply the whole village, and so have continuous current in them; I suspect mounting the unit next to these might be inadvisable due to the EM field?

marconi · May 5, 2019

One to check with the manufacturer - but I don't think EM interference from the power lines will be a problem though I would recommend you experiment first with position, height, elevation angle and direction of 'look' by the antenna relative to the driveway to confirm reliable performance to bowl out not only EM interference but nuisance detection caused by reflections from 'clutter' in the field of view. With regards to clutter think about objects that will be moved by the wind. Rain and snow might also set it off. This is the nature of MTI/doppler active radar detection - good clutter rejection (of moving grass say) is an important performance parameter alongside reliable target detection ( of the car). It is a difficult problem if the clutter spectrum and target signal spectrum overlap. You have got me reminiscing about a previous life.

Moving target indication - Wikipedia - https://en.wikipedia.org/wiki/Moving_target_indication

Mark42 · May 5, 2019

marconi said:
... This is the nature of MTI/doppler active radar detection - good clutter rejection (of moving grass say) is an important performance parameter alongside reliable target detection ( of the car). ...

Hi Marconi: Fascinating stuff, thanks for the post.

The device will be looking straight down the drive, mounted on one side (using the utility post if I can get away with it). There will indeed be long grass and crops on one side during the summer. The other side is a hedge which doesn't blow about much.

False radar signals might be a nuisance, but no one will end up being engaged by 30mm cannon fire

. I'll do some trials anyway.

From your name, not one of us are you?
Caister Marconi radio station contacts more than 160 amateurs in 36 countries | Southgate Amateur Radio News - http://www.southgatearc.org/news/2019/april/caister-marconi-radio-station-contacts-more-than-160-amateurs-in-36-countries.htm#.XM9EiRRKhaQ
73 de M0UMG/M0MUI/M0XUI (geeky family)

marconi · May 5, 2019

Re#19 - No, I am not a member of that august body.

telectrix · May 6, 2019

2.00 a.m.... cordless angle grinder, speed camera. modify triggering.

Mark42 · May 31, 2019

Job done!

As suggested, I fitted a Bircher 'Herkules' Doppler radar unit. It works brilliantly: solid discrimination between vehicles and people, with equally solid direction indication.

Not wanting to add to clutter, I fitted it on an existing utility pole at 3m up, on a small bracket to keep it away from the HV cables.

[ElectriciansForums.net] Detecting vehicles in one direction only. How to do it?

All parameters are settable in software. This device will do pretty well whatever you want it to, and is massively more reliable than PIRs.

As the Herkules' two volt-free relays give only a pulsed output on activation, it was necessary to fit a delay timer downstream in the home automation control panel, so it now acts like a standard PIR, with a selectable lights-on time after each activation.

I used a Radiospares Part No. 896-6813 Multi-function timer, which is very versatile, multi-voltage, and at £23 good value compared to branded alternatives.

So that the lights come on only after dark, the supply side of the multi-timer relay is fed by 24V from a dusk-to-dawn unit elsewhere in the installation.

The whole thing feeds into my lighting, heating and irrigation control panel in the kitchen.

This is a matrix: columns are inputs (Permanent-on, Timers, PIRs etc), rows are various garden lighting circuits. Any input may be assigned to any one or more outputs. There are no electronics, no touch-screens, nothing to go wrong for years!

Like I said before, it's not at all over-engineered.

telectrix · May 31, 2019

that's more over-engineered than Hitler's bunker.

DPG · May 31, 2019

That's completely over the top and unnecessary. What's the point?

But...... I love it!! That professionally made stainless panel is a work of art.

I approve!

Don't leave all your keys out in the open though - easy for thieves.

Charlie_ · May 31, 2019

Nice , I like it!
Is the front plate connected to earth

Mark42 · Jun 9, 2019

DPG said:
That's completely over the top and unnecessary. What's the point?
But...... I love it!! That professionally made stainless panel is a work of art.
I approve! ...

Ha Ha! Thank you for the kind comments

If anyone needs a custom control panel I recommend the suppliers I used: The Premier Engraving and Sign Co.

All you need is to draw the panel in any graphics app (I use an ancient version of CorelDraw), export to-scale as a .pdf or .eps then they do the rest, including telling you if anything doesn't quite work.