Ultrasonic Sensor Through a Wall/Door?

Projects General Guidance
1

Shower Thought Time!

Would it be possible to mount an ultrasonic sensor (e.g HC-SR04) on the inside of a wooden door, facing outwards like a peep hole, that would trigger a lightbulb when someone either walks past or is standing on the other side?

I have seen microwave sensors that will operate in this way but it got me thinking it could possibly be done with a cheap ultrasonic sensor.

HC-SR04
HC-SR04900×594 52.2 KB

This may be a complete oversight but can someone tell me where i would be wrong on this:

1. Ultrasonic can penetrate walls but would probably need an amplified signal to make it through a door and bounce off the opposite wall (maybe a lobby or hallway wall) and then back to the receiver?

>|--|| (> = HC-SR04, | = door, -- = signal, || = wall)

>|! || (! = object/human)

  • excuse the crude drawing

2. If you put a HC-SR04 up against the door, the signal is sent out (8 cycle sonic burst) and the receiver would immediately pick up the bounced signal from the door (how it was intended) and Pulse the Echo pin? But does the signal still travel through the wall/door/kitchen cabinet?

3. Would it be possible to modify the HC-SR04 circuit so that the receiver is set to ignore the returned signal for a certain amount of time (possibly by switching the receiver off for the amount of time it would normally take receive the signal back from an object up close) and pick up the stronger signal penetrating the door and bouncing off the wall behind the door? (picture a hallway)

This distance measurement could be set as default after measuring with no obstacles behind the door and then any change in this signal would be the trigger..

Does this sound plausible? Would the signal going through the door be obscured by the door's material, would the bounced signal be affected by the angles and never get back through to the receiver? Are these Ultrasonic Transducer/Transmitter's fairly directional?

Extra Questions:

• If I do have a basic grasp of how these signals are sent out, does that mean you could point a Transmitter at a pair of driving-robot eyes and have it stop (assuming it's setup to avoid walls)?

• is the exact same pulse sent each time or is it varied slightly to avoid echoes from older transmissions?

• If the transmitting signal was amplified on a HC-SR04 would the T and R casing be penetrated as the signal is leaving (i.e leakage)?

Anyway, i thought it was interesting and would like to hear any ideas on how this could be done or why it cannot!

2 Likes
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It's so easy to try.

1 Like
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No. The device is MCU based and has proprietary firmware. Well, at least not in any way that is worth the struggle.

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That is covered in the data sheet.

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ok, but the transmitter and receiver could be desoldered and breadboarded or my idea for disconnecting the receiver for a short time could work?

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Yes.

Not likely. The sound pulse will reflect on the door surface. If any pulse passes the wood it has lost a lot of power. The reflection pulse will loose more power passing back through the door. You will get one echo from the door, and maybe, maybe, get a very small signal from outside the door.

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Thanks Railroader,

If the signal was amplified to a point where the signal is coming back strong enough and the first echo was ignored do you think the signal would bounce back at enough of a horizontal/forward angle?

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Please go and do some experiments and come back. It will make for a much more fruitful discussion.

You float hardware mods, but are you experienced enough to design those?

Please do download and read the data sheet. It will save wasted time answering questions that are answered there.

1 Like
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It is simply a shower thought aarg, ordering parts takes a week for things to arrive, i wanted to ask someone who already had the knowledge (i thought the concept was interesting)

I wouldn't be designing much, i just had the idea the if the receiver is setup to finish that cycle once it receives the first echo i could disable the receivers power and delay for a short time, so that the bounced signal could then be the first echo received when powered back on.

I would assume with some thinking i can disconnect the +side of receiving transducers solder joint on the board and wire it back to the board but power it from an arduino pin?

That way i would be able to switch the receiver on and off at will (it was just an idea..)

I think a good way of learning is to ask questions and discuss, if it's wasted time, you don't need to answer but i thank you anyway and most of my questions are not answered in the datasheet

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if the transducers were mounted in the door directly (same distance apart but no casing) would that increase the likelihood of a second echo?

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At least one of your questions is answered there. Some of your questions involve more aspects than the sheet considers, your "extra questions"...

Thinking that you can disable the transducer by connecting it to an output pin, is, I'm sorry but the reality is, evidence that you don't have the skill to make any requisite modifications. Increasing the power of the transmitter could actually damage someone's hearing (although that one might just blow before that could happen).

I disagree that kicking around non specific questions is useful with ideas like this. What it really takes, is some research and some experimentation.

Microwave sensors will see through a hollow core door like it's glass. Why not use one? The modules are available for dirt cheap.

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Everyone has there ways of learning aarg, i have spent time reading datasheets, some people learn from video, some via text, some people learn best through auditory, why would asking some questions on a forum be a problem.

I didn't say i had any skills and i didn't say i was going to power it directly from the arduino pin either, but the pin could be the trigger for the extra part of the circuitry considering it would have to be controlled by the same sketch that is triggering the trig pin if the original circuit was to be modified.

The questions i asked seem all related and fairly specific to the idea that i had, i was just looking for more info from more experienced people (which i do consider part of the research process), I even mentioned more than once that i may have the idea wrong and asked to be corrected if that's the case, datasheet's do not contain all of the answers, isn't having a discussion about a topic, asking questions, getting answers and relaying back and forth the whole point, it's part of experimenting, playing around with ideas, i really don't see your problem.

You have good day now!

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Sure, it's just that you give the impression of being resistant to answers that contradict your idea. Then you float ideas that you can't actually implement. That means you need to engage peoples interest enough to contribute time and effort (significant if it means hardware mods to the board). Neither the request, nor the response, is mandatory. Everything is optional, posting, asking, replying. But you should consider the practical value of your methods of enquiry. Will your wondering, entice people to participate? Technical people are mainly interested in solid things, actual measurements and definite designs and plans. Not even having the device to play with, I would consider a very serious obstacle - then you can't test out ideas, they're just untested ideas that are only useful for debate.

And what is wrong with a radar module? :slight_smile:

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if you can drill one hole through the door, try the waterproof version.

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Another thing, there will be echoes inside the door material. The sound will follow the door frame and reflect when it hits the end of the frame. That will create false echoes.

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Because all you are really learning is that people have opinions on what they think you are asking.

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It's because nobody has actually done this, that the thread doesn't follow the normal here is the question, here is the answer format.

Instead, suggestions on how to investigate and experiment.

Because it's a self help forum.

Over and out.

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Sure, it's just that you give the impression of being resistant to answers that contradict your idea. Then you float ideas that you can't actually implement. That means you need to engage peoples interest enough to contribute time and effort (significant if it means hardware mods to the board). Neither the request, nor the response, is mandatory. Everything is optional, posting, asking, replying. But you should consider the practical value of your methods of enquiry. Will your wondering, entice people to participate? Technical people are mainly interested in solid things, actual measurements and definite designs and plans. Not even having the device to play with, I would consider a very serious obstacle - then you can't test out ideas, they're just untested ideas that are only useful for debate.

And what is wrong with a radar module? :slight_smile:

I am not resistant to any answers as long as they are constructive, "go and read the datasheet" isn't really a useful one, an expected one i will admit (maybe one answer regarding directionality of these transducers could be found in there).

It was more of a discussion on how a module built for one purpose might be re-used for another purpose, nothing wrong with that, any decent engineer does that all day long, make their own tools, strip old dead machinery down and re-use parts, I didn't float anything but ideas and isn't the whole point to work towards implementing them with some knowledge and other ideas from other people.

Technical people are mainly interested in solid things, actual measurements and definite designs and plans.

Some of them, yes, some of those "Technical people" also like to try new ideas and brainstorm with others, it's how new inventions are created and new things are discovered.

I do have some of the parts but the suggestion i made for disabling the receiver transducer would require ordering something else most likely, so why wouldn't i get more info first.

Another thing, there will be echoes inside the door material. The sound will follow the door frame and reflect when it hits the end of the frame. That will create false echoes.

Thank you - this is exactly the kind of response i was hoping for - ideas, discussion

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You have got to be kidding! !!!!!!!!!!!!!!!! That is engineering 101.

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yes, agreed, but not as the only answer