OK, and Thank You, "Y" for letting us know the frequency to use. Now the challenge will be how to avoid sharing the power.

 

I just want to point out that NFC tags are powered by the “receiver” in normal operation. That’s just how they operate.

There is a 13.56MHz signal transmitted by the receiver which is inductively coupled to the tag. The tag is powered by it, and to communicate with the receiver it uses load modulation. It can’t transmit so it switches resistors in and out of circuit to vary the load, and so the current draw, from the receiver.

The receiver decodes the changes as data.

I see, that makes sense, I was wondering why I kept seeing stickers with no talk of power supplies, but seeing the coils on the stickers themselves this makes perfect sense.

That however means I wouldn’t be able to have one antenna scan the whole board, as it would activate all pieces in range, so unless I want to calculate positions based on proximity or triangulation between antennas, I’d need a smaller antenna under each space, type PN532. I have access to plenty of NFC stickers, so it’s more so the reader that’s the «issue». I suppose one reader per square could still be made quite compact (and still cheaper than UHF readers), just a bit more wiring and programming, but that’s life when I complicate simple projects with arbitrary challenges

 

Is it possible to connect RFID antennas in a series of 64, all plugged into one Arduino? I can’t find any examples, but my aforementioned RFID reader does support series-connection…

If not, I suppose I could have 4 antennas plugged into one sub-microcontroller, and then have those be plugged into an Arduino, making the design modular, scalable, and a bit more manageable… Maybe?

 

While I don’t consider it particularly practical, given the relatively low frequency involved creating switching matrix using analog switch ICs that connects a single NFC reader to a set of antennas sequentially isn‘t outrageous.

Something like this max 1:32 mux from Analog, or something else—but you could have one reader and a buttload of antennas.

 

While I don’t consider it particularly practical, given the relatively low frequency involved creating switching matrix using analog switch ICs that connects a single NFC reader to a set of antennas sequentially isn‘t outrageous.

Something like this max 1:32 mux from Analog, or something else—but you could have one reader and a buttload of antennas.

Aren’t RFID antennas/readers real picky and stern when it comes to frequencies, Ohm resistances, etc? I’ve seen talks of needing all sorts of uppers and needing to ensure identical inductance in all components… But I have a very limited understanding of all this. One reader, two of those 1:32 MUX’s, and a whole headache of wiring… It could work… Not sure if this is the better approach for me, or having sub-modules with separate microcontrollers…

 

Certainly it will be mandatory to use the frequencies that the transmitters are built to use, and likewise the receiver uses. AND, it might work out to scan the receiver connection across the squares, powering each transmitter device one at a time.
I would not assume that an IC analog switch would possibly work, I would not even think that it might possibly work. It will take relays, 16 of them, to sequentially scan the 8 by 8 array. AND worse, they might need to be higher isolation rated REED relays. The great news will be that the folks at the "PICKERING" company are in the business of creating scanning relay arrays, and they can offer much more, and better, advice on that topic than I can.

 

Certainly it will be mandatory to use the frequencies that the transmitters are built to use, and likewise the receiver uses. AND, it might work out to scan the receiver connection across the squares, powering each transmitter device one at a time.
I would not assume that an IC analog switch would possibly work, I would not even think that it might possibly work. It will take relays, 16 of them, to sequentially scan the 8 by 8 array. AND worse, they might need to be higher isolation rated REED relays. The great news will be that the folks at the "PICKERING" company are in the business of creating scanning relay arrays, and they can offer much more, and better, advice on that topic than I can.

Seems multiplexing is more trouble than it’s worth, although doable, it might me beyond my competence level as of now. I’ll see if it’s possible to connect multiple of these readers in series, and if not, modular sub-micro units it is. Either way, RFID is more viable than expected, although the risk of readers activating and reading neighboring pieces still exists, but only some proper prototyping will show that.

Would love to multiplex antennas and just sweep, would make lighting the board easier too, but seems tough. Especially since the final product should ideally be 12x12 if not more (to allow for Ludo and other games too).

 

Multiplexing is not that terribly complicated, really. And in an array it actually is quite straightforward. In this application there would be only 16 relays, and only two at a time active. It will be rows and columns, exactly like a spreadsheet, but better defined and less prone to errors.

 

Multiplexing is not that terribly complicated, really. And in an array it actually is quite straightforward. In this application there would be only 16 relays, and only two at a time active. It will be rows and columns, exactly like a spreadsheet, but better defined and less prone to errors.

Multiplexing in and of itself is rather simple, it’s more so multiplexing RFID antennas that i’ve heard can be quite troublesome, going as far as the length of wire gradually impacting reading capabilities… But it’s not an idea i’m abandoning yet, just seems multiple readers is easier to set up, even if multiple antennas might be the more robust and reliable approach… Maybe if I find some specific pre-manufactured antenna and some reasonable analog switches I can have a shot at it, but I don’t have nearly the skill set to actually calculate impedances and lengths here.

 

In this application it will still be multiplexing coils that transfer energy to operate those small transmitters. The challenge will be how to reduce the range so that only one device at a time will hear and respond. So this will be a rather uncommon situation of limiting the range rather than stretching it.

 

The coils in the chess pieces are passive receivers so they are always ready to receive the power when it is available. THAT is how the computer knows which square that piece is sitting on. And the coils in the chess board must only have one switched on at a time for that reason. Also, only powering one at a time consumes much less power. So the whole system only needs one power generator and one RFID receiver.
Unfortunately I do not yet know exactly what frequency the power delivery system works at. BUT it might be similar to what they use for wireless cell phone charging.

So we did encounter the issued that RFID readers power passage tags automatically… I’m however researching listen-only readers, or potentially modifying tags with a customer power pickup-coil that gets powered by the board rather than the reader… Seems complicated, but doable, additionally there’s potential with BLE and Bluetooth Beacons and receivers… I’m not giving up on this idea yet, as it would by far be the most robust and efficient approach if possible, so I’ll either have to turn the power in a reader down to 0, have a custom listen-only reader, and/or heavily modify RFID tags… If not, 433mhz transmitters are rather small and modular, and using a DIP switch or some other form of data storage could make this an affordable and simple solution, although rather bulky…

Sadly not a lot of documentation online about listen-only readers, and modifying tags is difficult, but I’ll keep at it… Maybe BLE is the way to go…

 

So we did encounter the issued that RFID readers power passage tags automatically… I’m however researching listen-only readers, or potentially modifying tags with a customer power pickup-coil that gets powered by the board rather than the reader… Seems complicated, but doable, additionally there’s potential with BLE and Bluetooth Beacons and receivers… I’m not giving up on this idea yet, as it would by far be the most robust and efficient approach if possible, so I’ll either have to turn the power in a reader down to 0, have a custom listen-only reader, and/or heavily modify RFID tags… If not, 433mhz transmitters are rather small and modular, and using a DIP switch or some other form of data storage could make this an affordable and simple solution, although rather bulky…

Sadly not a lot of documentation online about listen-only readers, and modifying tags is difficult, but I’ll keep at it… Maybe BLE is the way to go…

The problem with the concept of “read only” is fundamental to how RFID works. You can’t do it. Here’s why:

As I explained before the key to RFID is load modulation. The tag does not transmit anything. There is no transmitter of any kind on the tag, it is only a receiver and a small processor. The HF signal of the reader is used to power the active electronics of the tag, and the data is sent by switching loads in and out of circuit on the tag resulting in changes of current in the reader.

It is by monitoring the power drawn by the tag that the reader can decode the message from the tag. Without being the source of power for the tag the receiver can’t see the message—it is not transmitted in any way a passive observing receiver could detect, again, the tag has no transmitter.

 

The problem with the concept of “read only” is fundamental to how RFID works. You can’t do it. Here’s why:

As I explained before the key to RFID is load modulation. The tag does not transmit anything. There is no transmitter of any kind on the tag, it is only a receiver and a small processor. The HF signal of the reader is used to power the active electronics of the tag, and the data is sent by switching loads in and out of circuit on the tag resulting in changes of current in the reader.

It is by monitoring the power drawn by the tag that the reader can decode the message from the tag. Without being the source of power for the tag the receiver can’t see the message—it is not transmitted in any way a passive observing receiver could detect, again, the tag has no transmitter.

Aha, I see, this makes sense, although I wish it were at times better explained online, so thank you. How does an active RFID tag work in that case? Either way, if a custom power-pickup coil won’t work… How viable is BLE and bluetooth beacons? Would actual radio transmitters like FS1000A be the way to go then?

Annoying, I already know GPT is unreliable and has a tendency to hallucinate, but in this case it has completely made up bullshit… Was hoping turning a reader down to 0dBm would make to read-only, but I realize now that’s stupid. Thank you for your patience, I realize I can be a brick wall, was just hoping RFID would be somewhat more feasible… I really don’t want to go down the route of IR-led encoding or whatever, but I might need to go back to the drawing board on this.

 

OK, and indeed "Y" has reminded me of just how the devices function. BUT ALL IS NOT LOST!! The work-around would be to multiplex the reader/power sender connection to each of the different coils, one under each square. While the technology would be a bit different, the communication would need to be a bit different, with a much shorter range. That would even improve acct=racy and possibly reduce the cost a bit. The software will need to access a 64 line table and record the results from the receiver as they are returned from each square. That part is simple. Now the time to do it is the limiting factor.
The process: Select a square, send the power, see the response, save the response at the address, advance to the next square address, repeat.
The big deal will be developing reliable short range magnetic coupling for whatever frequency is used.

 

OK, and indeed "Y" has reminded me of just how the devices function. BUT ALL IS NOT LOST!! The work-around would be to multiplex the reader/power sender connection to each of the different coils, one under each square. While the technology would be a bit different, the communication would need to be a bit different, with a much shorter range. That would even improve acct=racy and possibly reduce the cost a bit. The software will need to access a 64 line table and record the results from the receiver as they are returned from each square. That part is simple. Now the time to do it is the limiting factor.
The process: Select a square, send the power, see the response, save the response at the address, advance to the next square address, repeat.
The big deal will be developing reliable short range magnetic coupling for whatever frequency is used.

Do you mean multiplexing the antenna of the reader? As far as I’ve understood that can be rather cumbersome, posing some challenges when it comes to matching the exact frequencies and resistances across the board… Pre-made Antenna Multiplexers are expensive, and making one from scratch is a little complex from what I’ve understood, but it might be the way to go… Unless you had something else in mind?

 

The work-around would be to multiplex the reader/power sender connection to each of the different coils, one under each square.

I suggested this earlier. I think it could be done with an analog mux since the frequency is relatively low.

 

I suggested this earlier. I think it could be done with an analog mux since the frequency is relatively low.

I just struggle to find the correct components is all, the reader, antenna coils, mux, it would be a little expensive to accidentally have things not match up…

 

Aha, I see, this makes sense, although I wish it were at times better explained online, so thank you. How does an active RFID tag work in that case? Either way, if a custom power-pickup coil won’t work… How viable is BLE and bluetooth beacons? Would actual radio transmitters like FS1000A be the way to go then?

Annoying, I already know GPT is unreliable and has a tendency to hallucinate, but in this case it has completely made up bullshit… Was hoping turning a reader down to 0dBm would make to read-only, but I realize now that’s stupid. Thank you for your patience, I realize I can be a brick wall, was just hoping RFID would be somewhat more feasible… I really don’t want to go down the route of IR-led encoding or whatever, but I might need to go back to the drawing board on this.

You could use BLE because each piece would have a unique address but it is a complicated protocol and does need power. I might try to use a cheap 8-pin MCU like the ATTiny13A and power it inductively. The program would just wake up on power and generate an small low-frequency RF ID that could be recieved by a loop that surrounds the board.

I would bit-bang the RF from the GPIO. It would take a little (or maybe a lot) of experimenting, but it seems doable.

 

out of curiosity... what is the expected size of the chess board? something that can fit on a palm of the hand or something meant for mall or park? how about space under of over it?

 

My concept was a board the size of the traditional game boards, with the squares about 1 1/2 inches, so the 8 X8 board is about 12 inches on a side, close to 3x3 CM sort of. If the reader output is single ended, not balanced differential, so that one side id "common", then possibly analog switching rather than reed relays could be used. But I am not sure if IC devices can handle the power, since I don't know how much power is involved.