You've probably seen them. Those coaster or puck size electronic things they give you at a restaurant to buzz you when your food is ready.

A seemingly common element of their design is that they have a pair (sometimes more) of metal posts that (apparently) run through the device. These facilitate the stacking of the devices in to a pile on a charger. I assume the current just runs up the common bus created by the posts as they are aligned to be on top of each other.

Pager Tower

Another feature of the pager is that they occasionally strobe an LED. Mostly I think just to let folks know the things are alive and charged.

However, when combined in to a stack (both on and off of the charger), the pagers will orient themselves so that when the pagers strobe individually, they will do so in order, say, from bottom to top. Giving the entire stack an attractive, animated light display.

So, my question, is how do the pagers self orient? Given that their only connectivity is through the pair of charging posts? Now, they may have an optical sensor to tell them they're underneath something. The may have a magnetic sensor to tell them they're near each other. But I'm still not sure how they coordinate to determine not just who's on top or bottom, but, indeed, their place in the stack.

What are some mechanisms that can facilitate this kind of connectivity and ordering?

Addenda responding to comments:

The animation behavior happens on and off the charger. It's very possible the LED blink could be a PING of some kind from the central server ("not only is the puck alive, but the server can sense it as well"). It's possible that the pucks can talk back to the server. How would the puck know the ID of the device is was placed upon to relay to the server (or was placed upon it). If the server is driving the ping, then it's transmitting the ping packets in order, with the animation mind. If you have several stacks of the pucks, you will have several animations (though I can't say if they happen simultaneously, this is all casual observation in a restaurant). It's very possible the devices might have other optical or proximity sensors, but seems excessive to do that just for this feature, which suggests they manifest it with the hardware they already have.

No, I'm not familiar with the 433Mhz protocol.

  • \$\begingroup\$ Fascinating solution to a fast food service notice. WHere did you find these? Seems like a DC charger [port] for a Bluetooth communication product \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Apr 11 '19 at 17:16
  • \$\begingroup\$ Weight sensors would do :) But unlikely it is the actual way. \$\endgroup\$ – Eugene Sh. Apr 11 '19 at 17:17
  • \$\begingroup\$ These are common in Southern California. Some places put identifiers underneath the tables and the pucks can pick that up and relay to the base station what table the puck is on as well. \$\endgroup\$ – Will Hartung Apr 11 '19 at 17:17
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    \$\begingroup\$ Given that their only connectivity is through the pair of charging posts - I actually think these have some wireless connectivity, otherwise how will they "page" you? I'll expand on my previous comment - each time the pager is put onto or off the charger, it will send signal to a "server" - "ID such and such was just put/taken off the charger". The server will maintain the book-keeping of the order and synchronize the LEDs. \$\endgroup\$ – Eugene Sh. Apr 11 '19 at 17:23
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    \$\begingroup\$ @SunnyskyguyEE75 No offence, but it was partially unformatted dump of mostly irrelevant info. We ban questions written this way, and I don't see why would we pass such an answers too. Personally I tried to find the relevant part and I could not. \$\endgroup\$ – Eugene Sh. Apr 11 '19 at 17:44

Although this system may be offline from the internet the Server to Client communications must be shared over a 433 MHz channel using 4 digit address and data.

For IoT communication, these other forms were not used with the reasons given for IoT https://www.getkisi.com/blog/internet-of-things-communication-protocols

In this case, the communication bandwidth is low but addressable. Without knowing the intellectual property (IP) of this design, one can only guess how it is done. But most likely it is some form of server ( the listener to polls) to client ( the responder to polls) of communication.

How do coaster table pagers order themselves?

  • they respond to all inputs according to user interface and Server communication using the RF channel

how do the pagers self orient?

  • by the response to sequential polling from server and response on client LED display

What are some mechanisms that can facilitate this kind of connectivity and ordering?

  • Embedded "round-robin" Servo protocols and Wireless dedicated shared RF channels for Tx/Rx antenna.

Another example of a documented round-robin protocol which may be applied to a shared serial channel or a distribution channel or a shared wireless half-duplex channel



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