Pyscan - nfc badge reader

[corentin vercouter]

Hello,

we are on a project using pyscan to be walled in a building entrance where people will scan their badges. The badge's id will be send trough lora. The main goal is to use li-po battery so can a nfc tag wake up lopy4 from deepsleep ? The device have to be able to scan nfc badge 24 hours a day. Our goal is to have 1 year autonomy with 1500mah 3.7V battery.

If not possible do you have other suggestion to achieve the goal?

Thank you so much :)

[jcaron]

@corentin-vercouter an RFID badge is passive, it is actually powered by the reader, similar to wireless charging of phones (but the badge does not have a battery, it will only work while in the field provided by the reader).

So the reader normally is constantly on, providing power, and as soon as a tag/badge comes in the field, it will get the power and start working and the communication will start.

It is possible with some readers to switch the power on for a very short time, check if there’s a tag in range, and if not, switch the power off, wait a short time, and start again. It’s then a compromise on how frequently you wake up. The shorter the cycle, the quicker you’ll detect a tag, but the higher the power consumption, and vice versa. You also have to carefully calibrate how long the chip stays on to be sure to have enough time for the badge to wake up and initiate communication.

With most reader chips this needs to be driven externally by a controller. No idea if the chip used in the Pyscan has such a feature built-in, though I doubt it. And if it doesn’t, the LoPy deep sleep wake up time makes this just impossible, unless this can be done with the ULP co-processor or maybe the PIC on the Pyscan.

Note though that even if this were possible, I’m not quite sure exactly how low you can get. I would be surprised if 24x7 operation with a 1500 mAh battery yielded anywhere near a year.

Also, what do you intend to do with the data sent? Remember that LoRa is really a best effort network, and you probably shouldn’t count on being able to send tag info to the server and then get a response back about whether to open a door in a timely manner.

Personally, especially if this is security-related (rather than just informative), I would go for a wired device, possibly leveraging PoE (though some would object to an Ethernet LAN being reachable from the outside of the secured premises — this would require adequate filtering on the port).

Note that things are different if you are using a phone rather than a badge: phones can act as readers (or more precisely, some can), and provide the power to a badge or a “reader” which supports it (again, no idea of the chip in the Pyscan supports it, though I doubt it). But the details vary a lot between phones, and you could be more limited in what you can do. And of course it requires the phone to have enough battery.

[corentin vercouter]

@jcaron thank you for you long reply!

this device will be used as a time tracker (worker bage in upon arrival, worker badge out when leaving to home)

We went for lora, for its wide area of action with only one gateway.

thank you for your experience, i will suggest to bring 2 wires for supply purpose