a Lego block is pretty small. Many blocks are connected to more than one block. So, even for a single block you might have two type A chips and attached to them type B chips from neighboring blocks. Or vice versa with types. Distance between chip B2 and chip A1 might be a few centimeters, even though B2 couples with A2 and A1 with B1.
So can you localize RFID chips down to a centimeter of length? And even if you can, is the scanner that does that gonna cost a fortune instead of being an off-the-shelf dumb detector gadget?
Also, regardless of what Lego related stuff we are going to figure out here (it’s not like anybody gives a damn, and it’s not like I own a Lego factory), notice how much fight-the-ignorance info about passive RFID this thread has already explained. Well, more specifically, engineer comp geek has already explained by means of this thread :). If you google the subject, you get lots of chitchat about inventory systems, but you don’t get the straight dope on how the stuff actually works. So, I say, SDMB to the rescue. I want to understand this stuff, and I am sure there are other inherently curious people out there who will agree with me.
on second thought, yes, if the localization really can be accomplished down to the centimeter, maybe this approach would make sense for some applications, if not necessarily specifically for small block Lego. After all, presumably this scanner is already off the shelf whereas getting chips produced by the million is no small matter.
Well, so any input on the cost and spatial accuracy of the localizing scanner are also appreciated. It is always nice to study various approaches in detail.
ETA:
[QUOTE=abel29a]
If so, is it close enough if both chips are within reading distance of the RFID reader? (I’m assuming we’re talking close range 14443 proximity chips here - that is, 10-15cm reading range at most).
[/QUOTE]
no, I was thinking about scanners that work in the radius of 2-3 meters. Is that a problem for passive chips?
I’m just guessing here but I can imagine plenty of applications for such a technology. Wireless alarm/telltale sensors, being able to scan a car and find a broken/separated/worn component by sensor proximity, hard inventory locating down to inches on a large scale. Almost anywhere you might want to wirelessly detect point of contact/proximity.
When you say ‘off-the-shelf’ are you talking about something that you hope already exists? Because it sounds more like you mean ‘something that could perhaps be manufactured as a commodity’
in this thread I used “off the shelf” word only for scanners. I.e. I am discussing the possibility of making new-and-improved (for some purposes) chips that would work with existing scanners. Preferably cheap scanners.
Incidentally, depending on how easy it is to hack those existing scanners, I would be quite happy to discuss adjusting the scanner’s operation principle as long as it can be done in software. E.g. if it does time multiplexing of some sort, maybe interesting new behaviors could be obtained using an adjusted driver.
You can increase the power available by increasing the scanner transmitter’s output. The maximum power you’ll be able to output depends on what frequency band the scanner operates on. I think most of them are limited to 1 watt, which isn’t a huge amount of power.
You can increase the power available for brief use by shunting more of the incoming beam into charging a capacitor over a longer period of time. If you charge for twice as long and then use the energy stored in the capacitor, you basically have twice as much energy available, but you’ve doubled your read time.
Passive tags have a very short range, a few inches at best. Longer range RFID systems have a battery inside the tag.
so how long is a long read time? Is 5 seconds long?
Maybe this question should be elaborated as, does the read time depend on the expected number of chips in the area? Or does the scanner read 10 chips and 1000 chips equally fast/slow?
Why is the scanner limited to 1 Watt? And if we use this 1W scanner on a typical chip, how much power does it get? Is it 1mW? Or 1 micro Watt? Are there qualitative rules of thumb that could be used here?
thanks. It does give an overview that’s much better than the typical puff pieces bs online - e.g. the “singulation” issue is probably a part of the answer to my question about read speeds that I asked in post # 28.
But it is still pretty short on the technical nitty-gritty involved in groking any particular system (like our passive tags from this thread) even on a purely theoretical quantitative level. Obviously I will always be too ignorant to build even the simplest chip - but at least I want to understand how that chip and its scanner actually work, not just read the brief spec of the off-the-shelf all included system.
Of course, part of the reason for the above is that I am interested in potential new uses for existing technologies, whereas people who write such white papers are only interested in standard uses for them. So even if the spec is sufficiently informative to judge if it will or will not work for what it is intended for, it will not help me understand how easy or hard it would be to alter it, or something like it, to achieve some new useful behavior.
Passive tags, like the type printed on an RFID printer in a warehouse and attached to cartons or pallets typically have a range of 25 feet, not inches.