Opening Doors

Tonight marks a first for the Styra Project: We ordered a batch of custom printed circuit boards (PCBs). For perfectionists like James and I, it is hard to make the call that something is "good enough." And since this was our first attempt at designing custom PCBs, we wanted to get it right.

For the keyboard controller prototypes, we're investigating two different approaches. The first approach repurposes a device designed for building arcade cabinets. The Mini-PAC is a fully integrated keyboard controller designed for attaching arcade buttons, joysticks and other devices to a computer. This device is compact and inexpensive. It supports a large number of buttons and is potentially a fantastic fit for our project. The downside is that it is closed-source and only produced by a single manufacturer in Europe. The PCB board shown in Figure 1 will plug onto the Mini-PAC as a "shield" and allow the connection of up to 32 buttons using standard two-pin headers.

Figure 1: 32 input shield for Mini-PAC

The second approach we're investigating for the keyboard controller is one that leverages open-source hardware and software, specifically the Arduino Leonardo. There are several advantages to this approach, specifically that it allows for a great deal of flexibility in sourcing components as well as customization. Unfortunately the Leonardo does not have sufficient I/O inputs, and while there are techniques that can be used to add more buttons (charlie plexing / scanning/ bit shifting), I have decided that for the Styra Project it makes sense to create input modules that attach to an I2C bus.

Due to the limited scalability of using software debouncing, I decided to add hardware debouncing to the modules as well. Figure 2 shows the design for a 16 input module with hardware debouncing using entirely through-hole components. This design requires more components on the board, but is easy to solder. The EDE2008 chips used in this design have a debounce interval of 25ms, which is more than enough for the buttons we are using.   

Figure 2: 16 input module (version 2)

Figure 3 shows a second 16 input module but with a couple of surface mount components. This design utilizes the MAX6818 chips, which have a 50ms debounce interval and may feel sluggish to people who push buttons lightning fast. The layout is cleaner but the surface mount components can be a pain to solder.

Figure 3: 16 input module (version 3)

The PCBs will be on their way soon, and we will only have a couple more orders to make to have all our hardware for the project.

Finally, I would like to give a shout out to Roy Kimball for his design of the new Styra Project logo. His design was able to capture what this project is all about: opening doors.  :) We got it just in time to get it onto the PCB boards.