When I arrived at work this morning, the xEM in my foot wouldn’t read for a good 5 minutes. I was almost ready to call it dead when it started to ring again. I was out 2/3 minutes in the snow, so my feet were pretty cold.
That particular chip keeps getting chilled when I’m out, then super-hot when I warm my feet in front of the space heater inside (or when it’s summertime and the asphalt is hot), then cold, then hot all the time. Is it bad? I wouldn’t think so, but I can’t think of another reason why it would suddenly fail to ring, then start working again as it warmed up. Or maybe coincidence…
I’m pretty sure that the tuning will change with expansion / contraction of the ferrite rod and copper antenna coil. The difference in thermal coefficient of expansion between the materials doesn’t seem to be too much of an issue as I’ve tossed xNTs into liquid nitrogen and pulled them out and read them almost immediately, but
it’s possible the NFC transponders can put up with a lot more tuning variance … at least I’ve seen that they can in practice, but I’ve never tested 125khz stuff in the same way.
your reader might be more sensitive to out-of-tune transponders since it’s “high power” and usually high power stuff has a really hard time with S:N ratios anyway.
Perhaps someone with a thermal cycler would want to test some chips? I could send them some and we could run them from like -10C to 40C a few thousand times and see if they survive?
Then it would happen regularly. This was the first time since I implanted it - hence the worry: I’m concerned that it’s a sign it might be failing.
Yes. That’s how I knew it was the chip not answering: when I couldn’t log in, I presented my hand and the reader beeped.
I could do it: we have 4 temperature chambers at the office. They’re used to cycle our products from -35C to +65C at the end of production, for QC and for calibration. I could drop a chip in each of them and wait a few months. I think 3 of them cycle at least 20 times a week each during heavy production periods. But I have no spare DT chips to throw in them.
I guess if they survive that, they’ll survive anything: even when my feet are really cold and numb, they’re probably above freezing at the surface of the skin, and a few degrees above that just under it where the chip lives. And when they’re at that temperature, I make damn sure they don’t stay that way for very long. Our chambers stay at -35C for almost 10 minutes.
Speaking of testing - if my boss is okay of course - there is another device we have you might be interested in: we have a drop tester. Essentially it’s a carriage onto which we attach one of our devices, and we drop it repeatedly from a height of 2 meters until the device fails. It doesn’t get used all the time (just for product design and component supplier qualifications), but again I could tape a few chip to the carriage and leave them there. It probably does between 100 to 500 drops per month.
Nope: the reader worked fine with the EM in my hand.
I thought of all that too. The only remaining possibility I can think of is that it was somehow disabled temporarily, either by temperature, or by a loose solder joint - possibly the latter caused by the former. If that’s what it is, the problem is bound to reappear some day. I sure hope not…
Yes that’s right: the product is attached to the rail that’s screwed onto the sacrificial block of wood (the “impactor”). There’s a bit of unused flat space above the horizontal aluminum bar the block of wood is screwed onto: I’m thinking of taping a few chips there. They’re so light they won’t damage anything.
And of course, I can tape a few chips directly under the impactor, for repeated massive squashing testing.
Also, I’ve been meaning to add a proper hit counter to that device for a long time. I could simply add a reader at the bottom of the guillotine and catch one of the chips passing by. That would be a good occasion to implement a counter, and a dead-or-alive check for the chip at each hit at the same time. I could even ship the data to you, to add a live counter on one of your pages (as in, “that chip has survived xxx hits so far”)
My boss is cool. I don’t think he would mind, since there wouldn’t be any identifiable information in the photos or videos. But I still want to run that one past him because, well, I can’t just go misuse the facilities willy-nilly. Also, our product aren’t consumer products, and there might be restrictions dictated by our customers. But I doubt it.