Having seen a number of PCB business cards [Will] decided to go against the more popular choice of a micro-controller based design and show some character with a logic based finite state machine. [Will] uses a single 7-segment display to scroll through the letters of his name with a state machine that outputs the desired combination of 1’s and 0’s to the LED display each time the tactile button is pushed.
[Will] uses a 4-bit counter made up of D Flip-Flops for the clock signal as a conditional input to 6 of the 4-input AND gates. He doesn’t go into the painful details of displaying each character through the process (thankfully) but he does mention that he uses the Quine-McCluskey technique for reduction instead of Boolean algebra. Since his name is 11 characters long and the 4-bit binary counter goes from 0000 to 1111 leaving 5 more pushes of the button before rolling the count back to 0000, during which time the display is left blank. [Will] kindly includes the eagle and Gerber files for your downloading pleasure over at his blog if you’re interested in getting a little deeper into the design.
[Will] went with boards 0.8mm thin instead of the standard 1.6mm which affords more thickness for the surface mount parts. The BOM totals: 15 ICs, a coin cell battery, a push button, 7 current limiting resistors, and a capacitor as a hardware debounce. [Will] assembled them himself by hand placing the SMD components and left the soldering to his Reflow Château.
The use of logic gates instead of a micro-controller shows some understanding of logic based design, which is a bit rare when compared to hobbyists with some micro-controller knowledge. Not to say that the PCB business cards that include a micro aren’t impressive in their own right. If you need to brush up your logic chops there are a few recent posts that you might find useful: [Bil Herd’s] logic series, and [Al Williams] covered a browser based logic discussion of flip-flops.
Filed under: classic hacks, lifehacks
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