On a desktop computer, you think of an operating system as a big piece of complex software. For small systems (like an Arduino) you might want something a lot simpler. Object Oriented State Machine Operating System (OOSMOS) is a single-file and highly portable operating system, and it recently went open source.
OOSMOS has a unique approach because it is threadless, which makes it easy to use in memory constrained systems because there is no stack required for threads that don’t exist. The unit of execution is a C++ object (although you can use C) that contains a state machine.
You can read the API documentation online. Just remember that this is not an end user OS like Windows or Linux, but an operating environment for managing multiple tasks. You can, though, use OOSMOS under Windows or Linux as well as many other host systems.
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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.
Continue reading “This PCB Business Card Is Logically Different”
Raindrops on roses, and whiskers on kittens. They’re ok, but state machines are absolutely on our short list of favorite things.
There are probably as many ways to implement a state machine as there are programmers. These range from the terribly complex, one-size-fits-all frameworks down to simply writing a single
switch...case block. The frameworks end up being a little bit of a black box, especially if you’re just starting out, while the
switch...case versions are very easy to grok, but they don’t really help you write clear, structured code.
In this extra-long edition of Embed with Elliot, we’ll try to bridge the middle ground, demonstrating a couple of state machines with an emphasis on practical coding. We’ll work through a couple of examples of the different ways that they can be implemented in code. Along the way, we’ll Goldilocks solution for a particular application I had, controlling a popcorn popper that had been hacked into a coffee roaster. Hope you enjoy.
Continue reading “Embed With Elliot: Practical State Machines”