Following are the stages of the final project design, development and execution.
1. Basic electronic system layout:
Below is my first schematic sketch of the group of electronic devices that will conform my simple system. In this early version there was two power units, one for the coil and other for the microcontroller. Since it was not a very energy – efficient solution, I´ve looked into a way to have a single power source.
After consulting with a professor from the Mechatronics engineering department, he told me that is possible to get ride of one of the power sources by adding a 5V regulator between the power source and the microcontroller. This way one 9 V power source can feed both emitting coil and microcontroller (5V.) Below is my first rough sketch:
A second sketch, more detailed:
2. The Microcontroller:
For the microcontroller, I´ve decided to modify Daniele Ingrassia´s Satshakit, by adding a 5V regulator. This is in order to reduce the voltage from the 9V power source that feeds both the charging / emmitting induction coil and the microcontroller. This way I can use just one power source. A barrell connector for the power source was also added to the microcontroller board.
Below is an schematic of the modification to the Satshakit MCU, and board design in Eagle:
After reviewing it with a local guru, We´ve found that the vias exiting the regulator were wrong. This was solved in a further modification shown here:
The new MCU board redesigned in Eagle:
Here are the Eagle files of the MCU:
Some images of the (lenghty.. one day long…) milling process on the Modela:
The board with the components. I had to use what I have at hand regarding the power jack. Since it´s compatible with the 110/9v charger, just by twisting the contacts a little bit was enough to weld it parallel to the board surface. That way I´ll be able to save on vertical room and fit it inside my enclosure, flush to the table surface.
3. The optocoupler / MOC – triac mini board (Output.):
This tiny board will be connected between the 9v powersource, the microcontroller and the energy emitting inductive coil. It consist of a TRIAC type optocoupler which will receive an output signal to switch the coil on / off when a device is present or not over the charging coil base. These are the specs of the optocoupler:
Eagle schematic and board design of the optocoupler switch. I´ve added two series- connected 100 ohm resistors since I don´t have anything closer to 220 ohms:
Preparing the files for the Modela, and the (almost.) finished board. Just checking MOC fitting and orientation :
Here are the Eagle files of the MOC board:
Putting it all together. The electronic devices wired before installation. See notes.
6. Programming the MCU in Arduino:
As for the code to program the microcontroller, it was written in Arduino:
Checking the microcontroller using the original VCC / GND pins. everything ok..:
Checking the microcontroller using the 9V DC input. It was not ok… The power source have 1 Amp. The max resistance of the regulator was also 1Amp, so it overheated an probably burned out the regulator. But fortunately I was able to keep it working using the original VCC / Gnd pins that I had to solder again on the board..
5. The table / desk:
Since I want this project to be open source and doable by anyone with access to regular wood shop tools and nothing more sophisticated than a low cost FDM 3D printer, I´d like to use regular commercially available wood formats and measurements. This will also make possible of using these standard measures as parameters for design. The intention is avoiding the use of nails and screws. In order to assemble the wood parts I want to use 3D printed joints, in ABS or any other polymer with good mechanical resistance. The idea is to join the legs and top with nothing more than a circular table saw and a rubber mallet.
Some early development sketches for the table and 3D printed assembly joints:
Late development made in the 3D printing assignment. Although it worked well on small parts I do have doubts it can be stiff enough in a full size table.
A possible configuration of the final desk with their rechargeable devices:
After some consideration, I´ve found the newer assembly joints structurally better, but not very efficient from the point of view of cost, if 3D printing would be the method of choice. I´ve also thought of making a mold and casting it, but that would be a risk given the complex shape and the timespan needed to find stronger resins. This led me to a third design iteration, more simpler, using less 3D printed components, structurally sound and with a better cost.
The resulting design can be made using a 18 or 21mm thick plywood desktop, combined with a supporting structure made of 1 1/2″ diameter standard wood poles, made of locally reforested wood. Below is a preliminary sample of the slide / poster requested for the final presentation. (i´ts a sample, the final poster will include pictures of the real prototype:
Here are the STL files for all the 3D prints:
5. Desktop devices: Wireless rechargeable lamp.
For the lamp I´ve used an Adafruit 3.3V induction coil, which I´ve modified to include a rechargrable battery pack and an interruptor. In order to avoid burning the tiny receiver board I added a 2 Amp Si Diode. This way the lamp can be moved from its recharging station and placed elsewhere. Here is an schematic crude working assembly:
From this layout / component distribution, I designed and modeled a base that integrates the receiving coil, rechargeable battery and all the components shown above. The base consist of a lower and upper enclosure, with an operning on the top to fit the LED extension and the shade. The shade was 3D modeled in Alias, 2D developed as a flat surface in Rhino, DXF curves where obtained, which in turn were laser cut and engraved (the latter to make folding easier. The two parts of the shade are made of 0.6mm thick polypropylene, which was folded and spot welded with a hand held ultrasonic plastic welder.
Below are images of the lamp test:
