Simple Item Location Device (with sound)

I am in a 4th year project in University and I was looking to build a simple locating device for multiple items.

It would work like this:

  • Each item would have a tag/chip embedded in it (or retrofitted into the item)
  • There would be a board located on the wall that would have a list of the tagged items with buttons beside them. When the button for the item is pressed, the tag will “beep” allowing the user to locate the item.
  • I’m not looking for GPS capability, just when a button is pressed, the tag will beep.

Just wondering what sensors I would need to achieve this. Cost needs to be considered.

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Each item would need a beeper and a battery in addition to the tag circuit.

Each tag would also need a radio receiver of some sort e.g. NRF24L01 if its just inside a room
These would need to be powered on all the time, hence would have relatively short battery life

The device on the wall would need a transmitter to send a command to the appropriate receiver (tag), to tell it to beep.

If you are willing to wait a 10 secs between pressing the button and the "tag" beeping, you can make the batteries in the :"tag" last longer by only getting the arduino and the receiver to be active at specific time intervals eg, on for 1/10th sec every 10 seconds, gives around 100 fold reduction in power requirement and hence 100 fold longer battery life (approx)

I made a device with similar capability using IR - but radio may be more appropriate for your case if the devices could be hidden under books or whatever. The IR was jsut simple serial transmission.

My slaves were inactive for a large proportion of the time but rather than 1/10 sec every 10 secs I think they listened for a period equal to the time for 25 bits and if they heard nothing they went back to sleep for 250msecs. The receiver was designed so it would transmit the same data for longer than 250msecs so that it could be certain a slave would wake up during the transmission time. (I can't immediately find the code on my PC).

One of the complications with the slaves going to sleep is that some of the transmission must be wasted while the slave reacquires sync with the transmitted serial signal - that may be less of an issue with 2.4GHz wireless.

...R

The items will be hidden: under other items and could be in containers that are made of metal, wood or plastic. I’m also hoping that the tag could be moulded within the item so that it won’t change the way the user uses the item.
However having the tag moulded in would make it harder to change the battery. How long is the battery life on the NRF24L01 and is there a good place to buy these tags and batteries?

The battery life depends on the size (capacity) of the battery and the current drain of the entire circuit. Your entire project needs to be carefully thought through and realistically evaluated before any predictions can be made.