Make Electronics

Experiment 9: Time and Capacitors

68 Chapter 2

Experiment 9: Time and Capacitors

You will need:

• AC adapter, breadboard, wire, wire cutters, and strippers.


• Multimeter.


• Pushbutton, SPST. Quantity: 1.


• Resistors and electrolytic capacitors, assorted.
  In Experiment 8, when you put a capacitor in parallel with the coil of the relay,
  the capacitor charged almost instantly before discharging itself through the
  relay coil. If you add a resistor in series with a capacitor, the capacitor will take
  longer to charge. By making a capacitor take longer to charge, you can mea-
  sure time, which is a very important concept.
  Clean the components off your breadboard and use it to set up the very simple
  circuit shown in Figure 2-78, where C1 is a 1,000 μF capacitor, R1 is a 100K resis-
  tor, R2 is a 100Ω resistor, and S1 is the pushbutton that you used previously.
  Set your meter to measure volts DC, place the probes around the capacitor,
  and hold down the pushbutton. You should see the meter counting upward
  as the voltage accumulates on the capacitor. (This is easier with a meter that
  doesn’t have autoranging, because you won’t have to wait while the meter
  figures out which range to apply.) Resistor R1 slows the charging time for the
  capacitor.

Figure 2-78. Watch the voltage building up

on the capacitor while you hold down the

pushbutton. Substitute other values for

R1, discharge the capacitor by touching R2

across it, and then repeat your measure-

ment process.

S1: Momentary pushbutton, OFF (ON)

R1: 100K initially

R2: 100Ω

C1: 1,000 μF

61

R1

&1

R

Volts

12v

DC