BDD,
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A note concerning clock oscillators for future reference. You need not concern yourself right now with this information, but may eventually find it useful.
In theory, a clock oscillator's output has an exact 50 percent duty cycle. In practice, most oscillators will be anywhere from 45 percent to 55 percent. At low Ø2 clock rates such output asymmetry can usually be safely ignored. As you push the Ø2 clock rate ever closer to the maximum rating of the clocked device, output asymmetry has the potential to violate device timing and may lead to mystery problems. Jeff Laughton (Dr. Jeffyl) has a lucid discussion on timing at his website, which among other things, shows what can happen when clock asymmetry inadvertently bumps against device specs.
When I designed my POC unit I decided to run the clock oscillator's output through a flip-flop to eliminate asymmetry as a possible problem causer. Here's the circuit I used:
I might add the flip-flop anyway so that if I want to change the clock speed later I can just swap out the oscillator without having any concern over asymmetry at higher speeds.
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It's normal to have two kinds and sizes of capacitor: small ones close to each power-hungry chip, and a larger one close to the power supply point. Looks like the smaller ones are called bypass and the larger one is called bulk. 10uF electrolytic for the big one, 0.1uF for the small ones, maybe. Make sure the electrolytic one is the right way around. If you have inadequate capacitance, you could get unreliability, which is really hard to debug. If you don't get unreliability, you might mistakenly conclude that capacitance is unnecessary - in fact you'd be better off concluding that you were lucky this time.
I'll put a ceramic cap bypassing every IC and an electrolytic cap at the power supply header just to be safe.
Mike,
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Hi Billy. Welcome to the community.
A small microcontroller might also be used for a clock source with a relatively small foot print on your PCB. The crystal is actually optional if you can live with the ±1% frequency tolerance of the internal oscillator. In this case the extra pins could be used for a pair of jumpers to set the CPU Clock to 1, 2, 4, or 8-MHz during power-up or reset.
Have fun and good luck on your project.
Thanks for the warm welcome.
I like the additional control that an MCU would add to the system but I don't think that a microcontroller would fit with the feeling that I am going for. When I build a second system I may use some less purist component choices (such as GALs / FPGAs and MCUs). I will keep this idea in mind though (seeing as I can get most PICs or AVRs for less than an all in one oscillator).