Object identification

Projects General Guidance
1

Hi everyone,

I’m working on a project where I need to identify cylindrical objects (about 20 cm long and 3 cm in diameter) using Bluetooth Low Energy (BLE) beacons. Here’s the setup and challenge:

Project Overview:

• I have a shell-shaped holder where an object is placed.

• There are about 10 cylindrical objects, and only the one placed inside the holder should be identified.

• Initially, I tried using 125kHz RFID tags inside the cylindrical objects, but the reliability was low in this setup.

• I’m considering switching to BLE beacons for object identification, specifically using the DA14531 chip.

Problem Description:

• I need to reliably detect the object placed inside the holder while ignoring other nearby objects. The objects not in the holder could be just a few centimeters away, so near-field detection is crucial.

• I plan to use BLE advertising to broadcast a unique identifier from each object.

• My current thought is to use RSSI (signal strength) to filter out beacons that are not inside the holder. Additionally, I’m considering adjusting the transmission power of the DA14531 to limit the beacon’s range, ensuring that only the closest object (inside the holder) is detected.

Questions:

  1. Has anyone worked with similar near-field detection using BLE? If so, how reliable was it to use RSSI for detecting objects within such a small range?

  2. What’s the best way to configure the DA14531 (or any other BLE beacon) for low-range detection, so that only the beacon inside the holder is detected while ignoring the others?

  3. Are there better alternatives to RSSI filtering or transmission power adjustments for this kind of project?

  4. Any general tips on integrating DA14531 with Arduino for this type of application?

Thanks for any advice or suggestions! I’d appreciate any experiences or recommendations you can share.

2

What material are the cylinders made of ?

Are the ends of the cylinders open or closed ?

3

Hi, thank you for your help.

The tubes are made of plastic, and the extremities are closed.

4

I would hope the cylinders are a mix, which would require many types of investigation. "Does it conduct electricity?" "What volume/mass density?", "Does it resonate audio?"
Maybe a movable "claw" to help "thump" (solenoid + microphone), weigh (HX711), probe (DIO OUT 5v read by AIN pin)... and whatever other measurements you might want.

5

The cylinders are some kind of felt-markers.

7

I used "some kind of" because they are some kind of. The cylinders are refillable felt markers withs different felt-tips. some flat, some round, some 5cm large, some normal felt-marker tips. even the grip of the markers is of different diameter. The thinnest is 3cm in diameter and the largest is 4,5cm in diameter. They are all about the same length +/- 10cm.

hope that explains better what the objects are.

9

I mentioned the one with the size that fits all.
Meaning that if it fits inside the smallest, all others should be fine too.

10

Some word math:

"some kind of" != "The cylinders are refillable felt markers withs 
                   different felt-tips. some flat, some round, some 
                   5cm large, some normal felt-marker tips. even the 
                   grip of the markers is of different diameter. The 
                   thinnest is 3cm in diameter and the largest is
                   4,5cm in diameter. They are all about the same 
                   length +/- 10cm.

See post #4 for more...

12

YES, "some kind of".
I really didn't know that there is a clear "math" for the definition of "some kind of" if I explain my request for help using a more generalizing approach avoiding unnecessary esthetic details.

But anyway: I am sorry for being that unclear and disrespectful hiding indispensable informations and details!

14

You see how far I was off in Post #4... try narrowing the size of error I made.

15

Cutting to the chase...

So you want to put pens in holders and detect which pen is in which holder?

I don't think RSSI will be very useful: it varies too much depending on environmental conditions and whatever objects are nearby. What was the problem with the RFID?

17

Looks like it is one of those threads.

1 Photograph == 1000 words

Also motive is important, why are you trying to identify this?

1 Like
18

Hello to all, and thank you for trying to help me.

I realize it might be difficult to imagine what my intention is, so I’ll try to explain it better. This project is something I’d like to create in an arts class with some graffiti-interested kids.

Project Overview:

• Imagine a bucket on a table (in the upper right corner). The bucket contains felt markers, much like you’d find on an ordinary desk.

• At the front edge of the desk is a shell-shaped holder where one of the markers (taken from the bucket) can be placed.

• When a marker is placed in this holder, it should be recognized, and an explanatory audio or video file should be triggered (specific to the marker).

19

The most simple setup comes to my mind would be hf rfid stickers. Cheap and no batteries to maintain.
What was the problem with your lf rfid experiment?

20

we tried that. but the problem are the stickers that the kids peel off.
so we tried to put some tags inside the markers like the glas tags that look like pills.
but there we have the problem that these are very directional and only work reliably if they are perpendicular to the reader. And we had to put a lot of tags inside the markers.

21

You need higher power reader / better antenna, few stickers in different "angles" and non peelable tape on top.
What about qr-code reader?

22

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