MAKE IT VIBRATE - Vibrator Module for Casio F-91W

In this instructable, I will show you how I created a vibrator module for the F-91W Casio watch, turning beeping sounds into vibrations!

You all know the classic vintage watch Casio F-91W. I love this watch for its accuracy, vintage look, comfort, simplicity, all at a very low cost. I wear it almost every day without any defect, except one, an annoying electronic beeping sound if you want to wake up with the integrated alarm clock. This beeping alarm clock sound works well to wake me up, but also works with the whole house. Thus, I wanted to use the Casio F-91W alarm clock, but instead of beeping sounds from piezo buzzer, a mini vibration motor.

Animation of the (dis)assembling - Video made with Fusion 360 - Animation module:

For this project, I used these following parts :

• 1 Casio F-91W (a real one, will not work with fake models)
• 1 Coin Vibration Motors - DC 3V, 10 x 2,7 mm
• 1 MOSFET channel N 540 mW SOT-23
• 1 Schottky Diode
• 1 Ceramic capacitor - 22 nF
• 1 Resistor - 100 kΩ DCU 0805
• 1 Coin battery - CR1225
• 1 Coin battery holder for CR1225

I also used these tools :

• Soldering iron
• 3D printer

and these consumables :

• Tin wire or Solder paste
• PETG filament

The beeping sound comes from the paper-thin piezo buzzer bonded on the stainless steel back plate of the watch. On the PCB side of the watch, there are two springs which, once the back plate screwed in place, connect to the cathod and anode of the piezo. One spring leads to the positive (+3V) of the watch, the other one is connected to the watch calculator. An alternative signal is emitted between these two springs, goes through the piezo buzzer, making it vibrate.

I removed the back plate unscrewing the four screws. I measured the signal with an oscilloscope to analyse it. This analysis gave me a nearly squared signal of +3V amplitude, and have a 2.083 kHz frequency.

Nota : the Cathode probe was connected to the +3V Spring, the Ground probe to the other Spring.

To spin the motor, my first idea was to simply transform the alternative signal of the watch to a +3V DC signal to feed directly the motor. To do that I used a Half Wave Rectifier, with a diode and a capacitor. But it turned out that the rectified signal of +3V DC was not enough powerful to spin the motor up, given that the motor amp consumption is nearly 80mA!

My second idea was using the +3V DC rectified signal of the first idea, to control a MOSFET transistor which power the motor using a secondary +3V coin battery CR1225 (see the wiring diagram picture above), and it works just fine!

After some calculus and tests, it turns out that a 100kΩ resistor and a 22nF capacitor work best to have a nice and just enought powerful vibration.

Once I tested and validated the circuit to run the motor in Step 2, for several reasons I wanted to make the least bulky vibrator module. The motor and the coin battery CR1225 take up almost all the space, and I was almost obliged to go to the scale below for all the others components. So I chose to make it professional and tiny, using custom PCB and SMD componants.

For PCB editing and manufacture, I chose to go with EasyEDA and JLCPBC, It was my first time doing PCB and it was really easy.

PCB design details :

I chose a PCB of 2 layers, total thickness of 0.6 mm, made of FR4-Standard Tg 130-140°C.

All componants will be mounted on the upper surface, linked with 0.400 mm copper tracks.

On the bottom surface, I designed two large copper pads, in order to connect the watch springs (+3V Spring and µcontroller Spring). The Pulse Pad will be connected to the +3V Spring, and the GND Pad will be connected to the µcontroller Spring).

Note : The PCB in pictures is not the same than the model I'm sharing. When I validated in production my PCB V1.0, I realized a mistake too late, I inverted the Pulse Pad and the Ground Pad. The V1.0 module works, I just have to turn the PCB of 180°. Nothing to worry about in the Gerber file i'm sharing (V1.2).

Since I cannot upload the Gerber file, please ask me for the Gerber file in Private Message.

Back Plate - FDM Plastic Manufacturing :

Unfortunately, the vibrator module was to thick to fit inside the original stainless steel back plate. The module is 3.5 mm thick (0.6 mm from the PCB + 2.7 mm from the motor + 0.2 mm functionnal clearance). I had to design a new back plate, transforming the back plate into a back case.

Using Fusion 360, I've made this case respecting the bores location for the four assembling screws. Adding some space inside the case in order to fit the vibrator module. Using PrusaSlicer and my Prusa MK2S, I managed to print the back case, there are the parameters used :

• Material = PETG filament
• Nozzel Temperature = 244 °C
• HotBed Temperature = 90 °C
• Number of perimeters = 2
• Layer height = 0.2 mm

On the last picture of this step, you can see on the left side: the raw back case after the print, on the right side : the aesthetic back case mounted on the watch (sealed, sanded up to 500 grit, primed, painted black RAL 9005 and varnished with two coats).

In the end, the final thickness of the case is 4.9 mm, versus 2 mm for the metal back plate (2.45 ratio). The total thickness of the watch goes from 8.25 mm to 11.15mm, it seems to be pretty thick, but once weared on the wrist, the watch is still pretty good looking and comfortable to wear.

Back Plate - Metal Printing Manufacturing :

One of Instructables reader wanted to metal print the Back Plate in either Aluminum/Stainless Steel/Titanium. However, the wall thickness of the outside face is too thin for metal printing. The minimum is 0.8mm and the initial model is 0.5mm for PETG printing. That's why I've made another version of the Back Plate, only for metal printing with a 0.8mm thinckness for the oustside face.

As I raised of 0.3 mm the outside face thickness, the total thickness of the back plate is 0.3 larger, the final thickness of the case is 5.2 mm, with the metal back plate.

Please find below the back plate STL file I've made.

Everything on hand, it was "time" to finish the Casio F-91W with its vibrator module. This was the easiest and most satisfying of the whole process. I simply inserted the PCB inside the back case, making sure the two large pads were facing up. I placed the original seal for the water resistance property. I brought into contact the two pads of the PCB with the watch springs, making sure a good electrical contact was made. I gently screwed the four original screws with no over-torque and ... brrr brrr brrr!!! Some nice and smooth vibrations around my wrist instead of a beeping noise!

Note : I electric taped some parts of the PCB pads face (Motors Pins and Vias for the coin battery holder), in order to not have any contact with the +3V case of the watch battery.