Even with the previous generation of Mi Band, I experimented with introducing a contactless payment chip extracted from a bank card into the bracelet case.
Then the chip of the card was replaced with a key from the gate to the adjoining territory and from the entrance, which I was incredibly happy about, since I received the convenience and simplicity that is sometimes lacking.
However, over time, one problem arose that haunted me and poisoned the pleasure of the engineering delights I received – the release of new generations of devices, which means the need to extract my modifications and move them into the case of a new bracelet.
Firstly, it is not easy, and secondly, both devices – both the old and the new – are obtained with traces of parsing, which means that they can neither be realized, nor even donated to someone later.
These nuances made me think about finding a simple option for integrating the modules I needed into an actual wearable device.
The result of this research was the idea of placing the contactless modules not inside the bracelet capsule, but outside, on the strap.
Initially, with my inherent love for dismantling everything and everything, I decided to revive the old idea of introducing a chip into the body of the strap itself and began to think about how to do this so that the antenna would not break and break over time from constant bends of the strap.
All options were reduced to the need to create a compact version of the winding, which would coincide in width with the strap and at the same time would have a small length.
The payment for compactness in this case is the small range of such an antenna.
This is an unpleasant feature, but not critical, since it even improves the security of this solution due to the impossibility of remote scanning of such a chip.
But at the same time, the desire to hide everything inside the strap so that nothing would betray the presence of a modification created an additional problem in the form of the complexity of installation work, which means that it made this operation available only to a limited number of enthusiasts who were ready to take risks for an unusual solution.
Thoughts about this were not encouraging, because I wanted to make a massive solution that almost everyone could easily use.
I was prompted to solve this problem by chance. Having the fourth generation of the bracelet in my hands, I was forced to carry the third Mi Band with me, since inside it there was still a key to the local area, which I had to use almost every day.
This need annoyed me a little, and therefore, as a temporary measure, I decided to get the key out of the bracelet and adapt it to something else that is always with me until I decide to open the four.
The key has been removed.
In my case, it's just a chip and an antenna wire. If you do it from scratch, then in your case it will most likely be a round coil glued to some kind of base.
After removing the key, the first thought was to wind the antenna on the side surface of the capsule, and glue the chip itself on the inside of this very capsule.
The idea was dubious, and it had to be abandoned, since with this arrangement the chip turned out to be shielded by the bracelet stuffing and refused to fulfill its function. In other words, it just didn't work. And if it worked, then there is a risk of damaging it with a bracelet.
As the next solution that came to mind right there, there was a variant with a banal winding of the antenna on a strap in such a way that the turns of the antenna itself held the chip.
And this option worked – this solution turned out to be working, and the key perfectly opened doors and gates.
However, this temporary solution turned out to be unsafe for the antenna itself, which, with such an arrangement, was subjected to mechanical stress and could be damaged at the next contact with a hard surface.
Next came the idea to protect the antenna with something. This something, after the scotch tape, of course, was the heat shrink tubing.
And then I thought that if I'm still going to fix the chip and antenna on the strap using heat shrinkage, then why wind the antenna around the strap when you can make a compact module and attach it with heat shrinkage on the strap.
Such a solution will allow, if necessary, to simply cut the heat shrinkage and transfer the module to another strap. And given that heat shrink tubes come in different colors, there is scope for the choice of strap colors and even a kind of creativity.
And the price of the issue is cheap – shrinks are sold, for example, in FixPrice stores, already cut and in different colors (not advertising).
Actually, the result of this thought process was the option in which the contactless module and antenna look like a small module rolled up in adhesive tape (to protect it from moisture), which, if necessary, can be placed on any strap.
We wind the antenna using ordinary scotch tape as a base. We give the chip and antenna a rectangular shape that is convenient for our purposes, keeping in mind the width of the strap of the Mi Band 4.
We seal the resulting module with tape, and voila, the reusable blank is ready.
It's time to attach the module to the strap. This will require the previously mentioned piece of heat shrink tubing, a couple of minutes, and a heat source.
Moreover, if you do not want the chip to stick out through heat shrinkage, you can place it on the inside of the strap, placing under it, for example, a thin layer of any soft material that compensates for the protruding elements.
At the moment, this solution seems to me the most convenient and universal, given that the fitness bracelet is a regular guest on my right hand, and I see no reason to refuse it in the foreseeable future, which means that from a convenient contactless module on the bracelet strap also.
Instead of a gate key, an NFC chip from a bank card can also be used, or you can use them together – since there is enough space on the strap for two such modules.
Well, as a small remark, I must once again repeat the words that such a modification turned out to be appropriate and convenient for me. In no way do I impose this on anyone, and you yourself make the decision about the necessity or uselessness of such delights for yourself.