Experiment 16: Emitting a Pulse

Chapter Experiment 16: Emitting a Pulse

Make Electronics Book Learning by Discovery
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Make Electronics Book Learning by Discovery

  • Chips, Ahoy!153Experiment 16: Emitting a PulseExperiment 16: Emitting a PulseI’m going to introduce you to the most successful chip ever made: the 555 timer. As you can find numerous guides to it online, you might question the need to discuss it here, but I have three reasons for doing so:1. It’s unavoidable. You simply have to know about this chip. Some sources estimate that more than 1 billion are still being manufactured annually. It will be used in one way or another in most of the remaining circuits in this book.2. It provides a perfect introduction to integrated circuits, because it’s ro-bust, versatile, and illustrates two functions that we’ll be dealing with later: comparators and a flip-flop.3. After reading all the guides to the 555 that I could find, beginning with the original Fairchild Semiconductor data sheet and making my way through various hobby texts, I concluded that its inner workings are seldom ex-plained very clearly. I want to give you a graphic understanding of what’s happening inside it, because if you don’t have this, you won’t be in a good position to use the chip creatively.You will need:• 9-volt power supply.• Breadboard, jumper wires, and multimeter.• 5K linear potentiometer. Quantity: 1.• 555 timer chip. Quantity: 1.• Assorted resistors and capacitors.• SPST tactile switches. Quantity: 2.• LED (any type). Quantity: 1.ProcedureThe 555 chip is very robust, but still, in theory, you can zap it with a jolt of static electricity and kill it. Therefore, to be on the safe side, you should ground yourself before handling it. See the “Grounding yourself” warning on 187, page 187, 172 for details. Although this warning primarily refers to the type of chips known as CMOS, which are especially vulnerable, grounding yourself is always a sen-sible precaution.Look for a small circular indentation, called the dimple, molded into the body of the chip, and turn the chip so that the indentation is at the top-left corner with the pins pointing down. Alternatively, if your chip is of the type with a notch at one end, turn the chip so that the notch is at the top.The pins on chips are always numbered counterclockwise, starting from the top-left pin (next to the dimple). See Figure 4-13, which also shows the names of the pins on the 555 timer, although you don’t need to know most of them just yet.Negative(ground)TriggerOutputResetPositiveDischargeThresholdControl12348765DimpleNotchPins555TimerFigure 4-13. The 555 timer chip, seen from above. Pins on chips are always numbered counterclockwise, from the top-left corner, with a notch in the body of the chip upper-most, or a circular indentation at top-left, to remind you which end is up.