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Vehicle reversing sensors

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Sam Stones17/07/2021 21:27:58
867 forum posts
323 photos

Can U/S reversing sensors fitted to one vehicle respond to the emitted (U/S) signal from another?

Just curious,


Sam Stones17/07/2021 23:28:30
867 forum posts
323 photos

More of the story and the reason for my question.

While reversing from a parking spot in a very busy supermarket car park, the reversing sensor alarm came on and yet there was nothing close enough to activate it.

Then I noticed another vehicle with reversing lights lit about to back out towards me into the same lane.

Still curious,


Jon Lawes18/07/2021 00:44:55
882 forum posts

If its anything like aircraft radar, and the signal being transmitted by both was the same (same make and model of sensor maybe?) then I see no reason why one sensor wouldn't be spoofed by the other.

That being said it does expose my ignorance on these sensors. Do the different sensors on the same bumper not interact with each other due to a unique Pulse Repeition Frequency or similar? Interesting stuff....

Sam Stones18/07/2021 00:53:00
867 forum posts
323 photos

Thanks for your reply Jon.

For some reason (mainly my own ignorance) BFO also comes to mind too.

Were are the specialists when you need one? laugh



Bill Pudney18/07/2021 02:30:10
606 forum posts
24 photos

There was a time when I was just glad to get the reversing light on my MGBGT working!!



Martin Cargill18/07/2021 07:59:13
176 forum posts

Reversing light, you flash ba****d. I have the mark one eyeball fitted to my series Land-Rover. If that fails I revert to the mark one ear and park by sound, You just pull forward a bit after the crunch noise.


Nick Clarke 318/07/2021 09:18:00
1394 forum posts
61 photos
Posted by Martin Cargill on 18/07/2021 07:59:13:

Reversing light, you flash ba****d. I have the mark one eyeball fitted to my series Land-Rover. If that fails I revert to the mark one ear and park by sound, You just pull forward a bit after the crunch noise.


That sounds like the blind skydiver who knew it was time to bend his knees for landing when the dog's lead went slack! laugh

Clive Foster18/07/2021 09:55:37
3104 forum posts
107 photos

I doubt if there is anything more complicated than a narrowband filter in the signal path to ensure that a suitable signal is picked up.

However direct radiation from the source will be at a much higher power level than the normal reflected radiation so I'd have thought it would have saturated the input stage unless conditions were just so.

If it is just a simple frequency tuned system I'd expect it to be able to run at several different ones and cycle through the choices if one is obviously wrong.

Dunno if these are simple time delay devices or if they get a bit more sophisticated with a modulated pulse position or pulse width scheme. If there is amore complex encoding spoofing by another emitter can be made very near impossible.


SillyOldDuffer18/07/2021 10:01:10
8491 forum posts
1891 photos

I guess it could. Dunno if they're what's fitted to cars, but ultrasonic range finders work like sonar by sending a pulse and measuring how long it takes for the echo to return, if any. Normally short range (a few metres) because the echo is much weaker than the pulse. But I think the receiver would pick another car's sender up from several metres away provided there was nothing in the way.

The sensors work at between 35kHz and 100kHz, cost a few pounds, and are a popular Arduino project. An interesting variant might be to make an ultrasonic pyrometer for testing fireboxes. In principle, because the speed of sound depends on temperature, it should be possible to measure the temperature inside a firebox. Even more interesting to measure the temperature inside and along each of a boiler's fire tubes to see if their length and diameter is broadly correct. I suspect the innards of a model boiler are too small and inaccessible to get good readings, but it might be worth trying.


Michael Gilligan18/07/2021 10:11:49
20081 forum posts
1041 photos

Lots of good speculation so far … but nothing definitive

Wikipedia informs us that:

Toyota introduced ultrasonic Back Sonar on the 1982 Toyota Corona, offering it until 1988.[7] December 13, 1984 Massimo Ciccarello and Ruggero Lenci (see List of Italian inventors) entered in Italy the patent request for ultrasonics Parking sensors, and November 16, 1988 the Ministry of Industry granted them the Patent for industrial invention n. 1196650.[8]


So perhaps this is the place to start: **LINK**



Bill Pudney18/07/2021 10:49:19
606 forum posts
24 photos
Posted by Martin Cargill on 18/07/2021 07:59:13:

Reversing light, you flash ba****d. I have the mark one eyeball fitted to my series Land-Rover. If that fails I revert to the mark one ear and park by sound, You just pull forward a bit after the crunch noise.



Yep that's me, reversing lights, latest British technology...don't cha know............



Edited By Bill Pudney on 18/07/2021 10:49:43

John Haine18/07/2021 10:58:24
4626 forum posts
273 photos


Quite a long explanation of operating principle of at least one type.


This describes one that uses two transducers and how it can be used with an Arduino.

I have a vague recollection of reading an article years ago that described an ultrasonic FM-CW sensor rather than pulse type to get better accuracy at short range, though I'm not sure if any of the available sensors work this way.

Anyway it's clear that the sensors all use frequencies round 40 kHz and rely on some measure of randomness in the time alignment from other sonars to avoid interference. So it is very possible for the sensor pulses on one car to sometimes be picked up by those on another and interpreted as close-by echos.

roy entwistle18/07/2021 11:07:19
1504 forum posts

I don't know about reversing sensors but about Christmas I parked in a supermarket car park, locked my Corsa using the remote and the Fiesta at the side unlocked. I unlocked mine and the Fiesta locked. I'm afraid I locked mine and left the Fiesta unlocked. When I left later, the Fiesta had gone but my car was still locked.

Robert Butler18/07/2021 11:34:47
384 forum posts
6 photos

Wife's system is infallible, all dependant on hearing. When you either hear the crunch or can't reverse any further she becomes aware of the proximity of solid or unyielding objects. Absolutely foolproof and rarely fails?

Robert Butler

Calum Galleitch18/07/2021 11:52:24
168 forum posts
50 photos
Posted by roy entwistle on 18/07/2021 11:07:19:

I don't know about reversing sensors but about Christmas I parked in a supermarket car park, locked my Corsa using the remote and the Fiesta at the side unlocked.

Many years ago, my father, who was by trade a marine engineer, took a job in a motor garage after the collapse of the Clyde shipyards. On his first day, he was given the keys to a car - I forget the make but it was notorious for having only six different keyings - and drop it off, then walk half a mile and pick up another car of the same make at such and such an address. In a fit of absent-mindedness, he dropped the first car off, put the key in his pocket, walked to the new address, saw a car of the right make, put the key in it, and drove it back to the garage, promptly followed by the Old Bill, wanting to know why the garage had branched out into nicking cars.

Bazyle18/07/2021 18:22:00
6296 forum posts
222 photos

If asked to design a cheap as possible detector it would just produce a continuous output and measure the amplitude of the reflected signal. When it goes above a certain level assume it is from something close. So another one of the same make or equally cheap design would also set it off when back to back. lPlenty of ways to make it more sophisticated but all will be rejected by the accountants.

MGBGT reversing switch is notorious for failing and in a fairly awkward place to get to if I remember correctly.

Jim Smith 818/07/2021 18:33:13
29 forum posts
8 photos

I just designed an electronic schematic to use with a 4 Chinese sensor addon on the front and discovered a bit about these things: My schematic uses wheel speed sensors to blank it out above 3mph and activate it using the stalk switch when required. I tried leaving it on, but it kept beeping at kerbs and road furniture when pulling away from stops or closing in on other cars annoyed me.

They have a range of 1.8M and are dumb outside this range. They use a simple burst of 40kHz transmit and receive the time delayed (Doppler) burst to process it and get the distance. I can imagine a car close in front reversing might confuse it, but whilst it will probably use the same 40kHz, the pulse period frequency is unlikely to be the same? Continuous transmission from all 4 sensors would be a bit power thirsty for small scale electronics and where they use 4 sensors I think there is a timing difference set for each sensor. That's how (on my kit) they can have a bargraph displaying left right proximity. The processing knows which sensor is closest to the obstacle.

Edited By Jim Smith 8 on 18/07/2021 18:37:05

oldvelo19/07/2021 22:23:20
294 forum posts
56 photos


The developement of reversing radar as developed by my brother in law in the early seventies because of his concern for the number of horrendous accidents on open pit coal mines in the country

Reversing Radar

A little aside to the topic of it's early beginings

Sam Stones19/07/2021 23:53:55
867 forum posts
323 photos

Although as MichaelG suggests there’s nothing definitive (well not so far), I have found this short exercise an interesting digression.

Thanks to John, Dave (SoD), and oldvelo too for your links. Some of it was too challenging for my brain.

Roy, your experience with the Fiesta made me smile, although Robert, I’m not in favour of your wife’s ‘touch parking’ technique.cheeky

After all that, my guess is … under very rare conditions, there could be a false warning (albeit fail-safe) between cars installed with identical reverse-sensor-signatures, positioned back to back, and in line, but … ???

Samsmile d

From not-so-sunny Melbourne

Nigel Graham 220/07/2021 00:50:54
2031 forum posts
28 photos

Dave -

Interesting idea, an acoustic pyrometer. Unfortunately:

"The speed of sound depends on temperature..."

To a point. It actually depends on density. Whilst the density of a gas is affected by its temperature, it also depends on pressure, so the confining conditions and gas flow. I think the variability of everything in a miniature boiler would be nighmarishly difficult to analyse to the depth necessary.

I don't presume to deny it would not work but could be far trickier than it seems.


A humbling little digression.......

By comparison with Nature's been up to for some millions of years...

... bats have been using sound in the some-tens of kHz for social calls, and typically around the 100kHz mark for hunting and close-in navigation, no problem. The hunting also needs high repetition-rate chirps to aid discriminating insect prey of low sound reflectivity, from acoustically very difficult backgrounds in constant but random change. It probably uses interference patterns between the call and insect wing-beat.

Except that their upper frequency distance range is necessarily very short by signal absorption in the air and by the animal's very low call power. This is to some compensated for by high voice pressure-levels; in some species, handsomely exceeding 90 or even 100 dB re 20µPa: levels dangerous for us if within our hearing-range and at larger powers.

Think of being a little pipistrelle or horseshoe homing in on a fluttering moth against the constantly moving acoustic clutter of foliage. Just part of a very few grammes of brain working flat-out on very rapid, very complicated signal-processing necessary to control the responding flight, calls and ear-damping, while synchronising breathing with wing-flap and call. That mechanism maximises system efficiency by combining the chest muscles' contribution to exhalation with assisting the wing power-stroke. While it's at it, the brain's other departments are continuing to monitor and control the rest of the animal's physiology generally. All by instinct.

(The horseshoe bats call through their nostrils! Their characteristic facial folds are for call beam-focussing.)

Oh, and some of that compact brain must be holding some form of acoustic map memory back to the roost, especially vital to a nursing mother bat. They do have fairly good sight but that won't work in a cellar, mine or cave with no light whatsoever. Yet these lovely little creatures recall their way through what must be fiendishly complex acoustic "scenery" to where they sometimes reach.

What are we doing with ultrasonic location and ranging? (Actually, light on my car - a camera.) Using steady pulses and a string of 'beeps' to help us ease a big steel box into a shop car-park bay to the nearest foot or so usually in broad daylight, whilst knowing our "prey" is sitting perfectly still in tins and packets on the shelves....


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