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Old 06-07-2018, 11:15 AM   #14
dmjlambert
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Re: Any electronics nerds interested in Arduino/Atmel?

Yes, a spike after the transistor cuts off, you are right. A diode conducts electricity in one direction only, and does not conduct in the other direction. There is an arrow in the diode schematic symbol, that shows the direction current flows from positive to negative. So when the transistor is on and current is flowing from top to bottom in the schematic, the diode doesn't do anything. When transistor cuts off and the coil causes a more positive voltage to appear on the bottom contact of the coil compared to the top contact, the diode conducts to short out the coil and "use up" all the electricity in it.

Incidentally, back in olden days, somebody had to decide when talking about electricity, does it flow from positive to negative, or from negative to positive? In fact they had to decide what is positive and what is negative and what kind of symbols to use to picture it. Physicists have decided it is the flow of electrons in the wire that matters, and those flow from negative to positive. Electrical Engineers decided charges flow from positive to negative, and it has turned out to be the most common way of thinking about how electricity flows. That is a simplified explanation, but the bottom line it it doesn't really matter which flow you follow as long as you don't change your mind in the middle of reading a schematic. :-)
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