Lesson 21 Test Point 3—Introducing the Resistor/Capacitor Circuit

Chapter Lesson 21 Test Point 3—Introducing the Resistor/Capacitor Circuit

Electronic Circuits for the Evil Genius Second Edition 64 Lessons with Projects
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Electronic Circuits for the Evil Genius Second Edition 64 Lessons with Projects

  • The voltage produced at pin 11 pushes throughthe diode and gets trapped on the other side.Referring to the schematic in Figure L20-4, itwould be okay to say that the voltage and currentare trapped on the right side of the diode and notable to drain to ground through pin 11. It reachesground another way.Lesson 21Test Point 3—Introducing theResistor/Capacitor CircuitYou are introduced to a resistor/capacitor workingas a pair to control timing. You saw this brieflywhen you were introduced to capacitors in PartOne. This is called a resistor/capacitor (RC)circuit. This is actually one of the majorsubsystems in electronics used to control timing.Here it is used to control how quickly the voltageto the second NAND gate drains, which controlshow long the LED stays on. In an RC timingcircuit, imagine this: The capacitor is like a sinkand holds the charge. The resistor is like a drainpipe. It allows the charge in the sink to flow out.Note that TP3 can be considered anywherealong the common connection of D1, R2, and C1and pins 1 and 2. They are all connected togetheras they are shown in Figure L21-1.Record all of your results on the data table atthe end of Section 6.1.Before you take any measurements, allow thecircuit to remain unused for at least a minute.Measure the voltage at TP3 with the pushbutton plunger untouched and record yourresults.2.Measure the voltage at TP3 with the pushbutton held closed and record your results.Figure L21-2 shows that as long as the NANDgate’s output at pin 11 is high, the voltage andcurrent push through D1 and do two things.They influence the inputs of the secondNAND gate and fill the capacitor.3.Now keep the probe at TP3. Release the pushbutton (PB) and watch the DMM. Whathappens here is completely different from TP1or TP2. The voltage slowly decreases. If youare using a poor-quality DMM, the voltageLesson 21 ■Test Point 3—Introducing the Resistor/Capacitor Circuit 83Figure 20-4Figure L21-1Figure L21-2