led discharge circuit

Posted on Feb 5, 2014

It`s enough to explore PWM and digital-to-analog conversion, and it illustrates how you can create your very own electronics workbench to explore RC filters , charge curves, discharge curves, pulse generators, timers, and even create a very simple oscilloscope to understand what`s going on in a dynamic electronic circuit. The first thing I need to do is clear things up a bit. While

led discharge circuit
Click here to download the full size of the above Circuit.

that above picture is a fully functioning circuit, it`s pretty awkward to see exactly what is hooked up to what. Some of these components are polarized, so there`s in fact more to it than which wire goes where . First thing to notice, is that there`s a lot more info here, and it`s a lot more precise. The components use a standard notation, and their values are also indicated. Now, although it was a fun exercise for me to draw this by hand and scan it in, it`s a bit tedious if I make mistakes while drawing or when things change. Fortunately, there are computer-aided design ( CAD ) software packages which make it simple to draw and edit such schematics on-screen. Here`s the same schematic using EAGLE : But this is where the fun starts. We could just hook up a battery to it (+ to VIN and to GND), and there would in fact be some interesting behavior. But we can do a lot better than that: we can put the entire circuit under computer control! The digital output pins on an ATmega are terrific controllable power sources, as long as we only need a few milliamps at 3. 3V or 5V. And if we need more well, that`s where transistors come in (to be described in a future post). The other great property of an ATmega (many MPUs, for that matter), is that they also have analog and digital inputs, so they can be used to measure various aspects of the circuit under test at the same time. I still haven`t told you what the circuit does. But if...

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