Skmei 1123 with Casio F91w module
A few days ago, reading in Javier Gutiérrez Chamorro's blog an article about the Skmei 1123, in the comments the user Angel raised the question about whether it would be possible to combine a Casio module 593 with the skmei 1123.
Taking advantage of the fact that I had a 593 module of the Casio F91w to spare, I set to work. The goal was to see if the Skmei's module could be replaced with the Casio's, leaving a Skmei watch with a metal alloy case with the Casio module.
We began by disarming the Skmei 1123
The first thing was to disarm the Skmei step by step.
First, we have to remove the screws from the Skmei's back cover. The screws are smaller than the typical casio screws and of worse quality as we will see later.
Once removed, we remove the back cover and we can see the Skmei module.
Comparing the guts of the Skmei 1123 and the Casio F91w
The first pleasant surprise of the Skmei is that the buttons are attached with the traditional circlip method, so they are easily removable to clean the dirt that accumulates and makes it difficult to operate.
Rear cover gasket
The back cover gasket is another element where cost savings are noticeable. Unlike the Casio's gasket, which is perfectly profiled without "burrs", the Skmei's gasket appears to be poorly profiled.
With respect to the module, this is where the difference in quality between the two watches is most noticeable.
As we can see, the first difference is that in the Skmei 1123 the metal case that holds the battery is screwed on. In the Casio, it's hooked in with some tabs.
On the circuit itself is another aspect where Casio demonstrates its quality. It looks much more elaborate than the Skmei.
A positive point about the Skmei is that it comes standard with a Maxell 2016 battery, it's great that it's a quality battery and not the typical Chinese generic one.
The screen looks much better on the Casio. Besides the fact that the digits are thicker (a little more, but it makes it look better), it has a higher contrast with the background.
It also has better viewing angles, when you look at the Skmei's screen from the side you can see too much of the segments of the leds that are off. This makes it difficult to see the time correctly from different angles.
Problems with module transplantation
Since not everything was going to be as easy as removing the module from the Skmei and replacing it with the Casio. The main problem is that the Casio's module is smaller than the Skmei's. There is little difference (it must be 1 or 2 mm difference).
Also the shape of both modules is different. The Casio has a much more rounded shape, and the metal button terminals follow the round contour.
In contrast, the Skmei is less "round" and the button terminals are completely straight. This makes the terminals closer to the buttons and with the button travel they make contact on the module without any problems.
This difference in the dimensions and shape of the module generates two problems: the module is not fixed inside the box and can rotate freely, and the buttons do not have sufficient travel for the terminals to contact the module. This makes that even if we press the buttons "they don't work".
Since the idea was to make a quick adaptation, I try to make the big mess: "fit" the module with some small pieces of thin cardboard on the button terminals. This also makes the terminals touch the circuit and the buttons work correctly.
Finally, there is one small detail. The pin that is in contact with the piezoelectric speaker in the rear cover is not in the correct position, so it should be carefully turned upwards.
Once the cover is put on without screwing, we check that the sound works (although very low) and the buttons also work, we grease the gasket with silicone grease and close the watch.
And here another problem appeared: the quality of the screws is very low. In spite of using a quality screwdriver, the screw material is very soft and the head started to come apart. As they are smaller than the leftover Casio I have around here, I don't take any risk and I don't try to open the watch again to adjust the sound pin contact better.
Obviously, it is a botched adaptation, we should do it differently to have more guarantees of not having problems in the future. Surely, using double-sided tape on the back of the glass to fix the module to the glass so that it does not move. And use some kind of putty on the button terminals to cover the remaining distance of the Casio module to the buttons so that they work properly.
But I'm happy with the Skmei F91w 😉 After all, the clock is operational and you can see a substantial improvement on the screen. You can read the time much better as it has more definition and contrast and even if you tilt the clock a little you can still see the digits correctly. As you can see in the picture, the module is a little bit turned and the hour digits are not straight, but for now it will stay like that.
About the Skmei 1123 I can say that I think it is a correct clock, although it can be improved. It should improve the visibility of the screen and above all improve the quality controls, thus avoiding modules with an excessive advance/decline for a digital clock.
In my case, I've been lucky and it seems pretty accurate (+0.9 seconds a day). The problem is that it's a lottery, and that you can get a unit that goes forward or backward much more, making the clock almost useless. In Guti's blog article, he quotes that his unit has a +2.6 seconds delay per day, too much for a digital clock.
On the other hand, Casio should get its act together, since it has more and more competition and brands like Skmei and Sanda will make things more difficult for it. If I were to develop a model with the f91w module, with a metal and glass case, I would sell them like hot cakes. If a brand like Skmei can, a giant like Casio can too.