DIY Watchwinder. 2018-08-22

Automatical and mechanical watches have power reserve of 30-50h. Leaving them unused for more than that will make the watch stop, and you have to wind it and set time and date. A watchwinder can be used to keep "power reserve spring" winded for a longer time.

It's not recomended to leave a watch on winder for months because the spring needs to rest if the watch is unused. But it's perfect when the watch is laying still for a weekend or so!

When building a winder it's a good idea to have as few RPM's as possible, just to keep the watch winded but not more!

Fortunatly i have a power reserve meter on my Seiko watch where it shows how winded the watch is measured in hours. I  will use this feature to really set proper RPM and not overwind the watches, of course with some added marginal. At the moment it keeps the watches winded but i don't know how much.

I decided to etch the PCB, so the esthethic result is not that great but it works well. The program is simple and can be downloaded for the 16F1847 mcu used for this project. I use two SMD H bridges which can be powered with 2.2V-6V so they will be able to power almost all small motors used. They H bridges are supplied by an adjusatble regulator to set preferred voltage by a voltage divider.

The housing is built of 0.6mm plywood as the cower is bent and 2mm plywood for the sides and bottom.

Also some 4mm balsa was glued to reinforce the bent plywood after it was glued together.

Unfortunatly the casing acts like a guitar and the otherwise really quite geared motors where loud enough to disturb when mounted in the casing. I damped the wood case with asphalt sheets and lowered the motor speed as musch as possible. It helped alot but i never got really satisfied with the noise levels.

First the motor was mounted into the case and i was relying that the tilt of the top was enough to rotate the winder weigth but i needed to add more angle to move the weight. Therefore i 3D printed a small extra console for the motors with greater angle.

The mechanical assembly is 3D printed and both looks and works great. I had to reprint a couple

parts due to the fact that printed parts shrink and holes become to small. Adding 10% on hole dimensions and so will make the real printed part fit perfectly. So a thumbrule is 10% shrinkage.

One watch "pillow" is for smaller watches and the other one has added foam to increase the diameter for bigger watches.

GSM IO module. 2018-05-21

Designing a universal module with one 12V input, one 5V IO that can be configured as ADC input and one output that can deliver +5V/~300mA to control external circuits such as relays. I also wanted to use a of the shelf box.

Made a tight power desing with a internal 3A LDO which is intended to be powered from a 5Vusb power supply. Also tried to have a small form factor and use the Hammond 1551RBT enclosure.

As few components as possible were used and PIC12F1840 is used as mcu.

Second time i use the SIM800L module. After this project i can fairly admitt i was lucky with my first project having no issues with the module.

First of all this module can require up to 2A current supply in worst case, this is mainly for short periods but will display if your power design have any flaws. In my previous project i was lucky using a big 7805 reugualtor powered from 9Vdc.

With the tight power design i thought it would be enough to supply the module with 5V and have internal system voltage on 4.6V. It did not work, the Sim800 module did not get enough power when connecting to the GSM net. The solution was to increase the internal voltage to 4.84V and to find an USB charger with higher output voltage than 5V. The Apple 12W charger is the far best alternative for this module. It outputs 5.2V and 2.4A.

Finally there were alot of issues with antenna placement. This module is physichally small and the antenna is close to the electronics. Often the antenna disturbs the GSM module making it lose GSM net and resetting itself.

After many attempts the final solution was to add some copper tape connected to ground as shielding between antenna and module!