From the initial design sketch a specification began to emerge. Top of the list it had to be easy to use. Despite not using a full keyboard I wanted the user to find it easy to interact with the Raspberry Pi. Selecting a menu option needed to take seconds and the buttons had to fall under a user's fingers. It also had to be easy for the programmer, no harder than getting user input from a keyboard.
Next on the list, was that the control and display unit mustn't be bigger or more expensive than the Raspberry Pi itself.
At this stage I wasn't sure if the specification was too ambitious. I needed to build something easy for users, and developers and within the size and price of a Raspberry Pi! To find out if was possible, it was time to build one!
I had a rough idea of what was important to create a friendly user-interface. If nothing else, the toil of setting the time on digital watches using two buttons told me what not to do! Instead, what was needed was more inputs, arranged in a natural way. I wanted something that would make it easy to select an item from a range of options, or jump to a particular menu. It was time to scour the 11500 switches and 2000+ displays on the element14 website!
With a few components identified as options I started creating footprints to design the PCB with CadSoft Eagle. I already had the outline of PiFace Digital that fitted well on top of the Raspberry Pi, so I used this the target area to fit a display and various controls. After a few days I was beginning to despair at Pete Lomas' excellent, some could say magical, work in getting a Raspberry Pi as small as it was; my early designs for control and display had parts overhanging the boundaries of a credit card!
Eventually I had a couple of physical layouts that looked viable and the next step was to add the electronics that made them function. With the parts ordered from element14 and a few days of design iterations later and it was time to order the PCB. Despite the number of PCBs I’ve created, whenever I order one, there's always an anxious wait to see if I've done something stupid and created another fibreglass coaster...
For more information or to buy , visit PiFace Control & Display