TAILIEUCHUNG - Practical Arduino Cool Projects for Open Source Hardware- P4

Practical Arduino Cool Projects for Open Source Hardware- P4: A schematic or circuit diagram is a diagram that describes the interconnections in an electrical or electronic device. In the projects presented in Practical Arduino, we’ve taken the approach of providing both a photograph and/or line drawing of the completed device along with a schematic. While learning to read schematics takes a modest investment of your time, it will prove useful time and time again as you develop your projects. With that in mind, we present a quick how-to in this section | CHAPTER 1 INTRODUCTION There are at least three parameters that you need to consider when selecting diodes for use in your projects these are Current-handling capability Diodes can only pass a certain amount of current without damage. Small signal diodes like the venerable 1N4148 1N914 can cope with about 200mA Rectifier diodes like the 1N400 are good for an amp or so for higher ratings you ll find plenty of options at your favorite supplier. Maximum reverse voltage Diodes can only cope with a certain amount of reverse bias voltage before they are damaged. Again looking at our two usual suspects of the 1N4148 and 1N4004 the maximum reverse voltage is 100V and 400V respectively. Forward voltage drop Nothing comes for free When conducing forward biased the diode drops a certain amount of voltage across its terminals. This of course ends up as heat and so diodes have power limitations as well. The 1N4148 and 1N4004 have similar forward voltage drops of 1V. A common use of a diode is to avoid damage to a piece of circuitry if the power is connected back to front. When using diodes in this manner you need to consider all three of the previously mentioned parameters particularly the current-handling capability is it high enough and the forward voltage drop are you going to end up with a marginal supply voltage because of it An alternative approach is to use a diode connected across the power supply input such that it only conducts if the power is connected back to front. A quick blow fuse must also be used so that the diode doesn t stay conducting all this power for too long. The advantage of this approach is that you don t get the forward voltage drop the drawback being you blow a fuse and if your design is marginal you may blow the diode negating the protection circuit entirely. Some subtlety is called for with this one. Power Supplies There are many different ways of powering your Arduino project. Low-power Arduino projects can be powered from either the host PCs USB

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