The first board for the Dave's Digital Design Doohikey boards is the 555 Timer Pulse Generator. This board is intended to provide a clocking source for digital projects. The uses a classic 555 timer, with a Schmitt trigger to clean up the signal. I've added in a switch to select between 2Hz and 10Hz frequencies. The 2Hz frequency is slow enough to easily look at events being clocked, but fast enough not to get annoyed. The 10Hz frequency is just fast enough to get things done quickly, but not so fast that it happens in the blink of an eye. I've also added a switch to change to "single step" mode. A button press provides a single clock pulse to the system, which is great for debugging. This board includes a barrel jack for power. I don't plan to put on on all of the boards, but since this is one of the boards that "starts a chain of boards", it makes sense to put one on it.