Main PCB for displays
The main printed circuit board for the DSKY is submitted to the fabrication service, PCBWAY.com who are sponsoring our projects by providing free PCBs. In this case it is a good thing, because the tight spacing in the aluminum DSKY case required a 10 layer PCB, 6 1/2" by 4 1/2", to accommodate all the circuits needed and provide the displays in the correct layout.
|DSKY case given to me by Jimmie, into which I will install the DSKY substitute, before cleanup|
Keyboard section design
I turned my attention to the design of the keyboard portion, which houses the 19 pushbuttons at the bottom of the DSKY. These buttons are about 7/8" square, internally lighted through the key legend, and must provide a distinctive feel when operated. They move down about 3/16" before activating and bottom out at 1/4", requiring about 24 ounces of force.
My keyboard section has to generate a signal when any button is pressed, a five bit keycode designating which of the keys is pressed, and discrete signals for the RESET and the PRO keys. PRO does not produce a keycode, just the PRO signal, while the other 18 keys generate a keycode and RESET produces both.
I intend to use a small microcontroller (Arduino Nano) on the board to read the pushbuttons and generate the 8 signals (keycode and three discretes), since my main board expects these. I could use a diode matrix and logic chips, a bit more work to design and requiring more space and complexity for the PCB.
I have selected an E-Switch pushbutton that gets me partway to the required behavior. This switch requires about 600 grams of force to travel 2 mm. I need to travel 6.35 mm and have about 675 grams of resistance. The solution is to install an outer button with a compression spring, which adds 4.35 mm of movement and adds 75 grams of resistance in that movement. The net travel and force will fit the specification.
I am using Fusion 360 to do the mechanical design of the keyboard - built into a large honeycomb 3D printed plastic part will sit inside the aluminum DSKY panel and attach to a printed circuit card at the bottom. The pushbutton is installed on the PCB and surrounded by a few small LEDs to create the backlighting.
|Beginning to model the case|
|Transparent inner piece that fits over pushbutton with spring inside|
It will cost roughly $100 to manufacture the translucent keycaps, somewhat less for the honeycomb since that can use inexpensive plastic, and then there are the parts costs of about $75 for the components to sit on the PCB. Overall this DSKY will probably cost me $600 to $700 even with the free PCBs. Hobbies get expensive.
It has been quite a few years since I used Autocad, the basis of Fusion 360. The (re)-learning curve is still steep, but I am battling through the production of all the mechanical components that will be assembled in the DSKY. So far, I have the base of the aluminum DSKY housing, the inner piece the will slide up and down, and have begun on the faceplate Friday afternoon.