-31-
In this project, you use a capacitor’s charging and
discharging to dim a light (an LED in this case).
When you finish the wiring, set the switch to A. The
LED segments slowly light up, displaying an L. In a
few seconds, the LED reaches its brightest point
and stays on. Now move the switch to B, and the L
gradually fades away.
Take a look at the schematic. With the switch on,
current flows from the battery to charge the 100
μ
F
capacitor. As the capacitor approaches full charge,
more and more electricity flows to the base of the
transistor, gradually turning it on (and thereby
turning the LED on). When the capacitor is
completely charged, the current continues to flow to
the transistor base, and the LED stays on.
When you turn the switch off, you remove the
battery from the circuit and the capacitor begins the
discharge through the transistor and the LED. The L
gradually dims until the 100
μ
F fully discharged.
If you want a slower dimmer circuit, replace the
100
μ
F capacitor with the 470
μ
F capacitor. Simply
replace connections 25-116-124 with connections
25-118-124, and replace connections 46-115-124,
and replace connections 45-115-90 with 46-117-90.
You’ll have to be patient, but the LED comes on
eventually.
Now go back to project 8 (Electronic Siren) and see
if you can figure out why the siren sound goes from
high to low as you press and release the key.
Hint: when you close the key the 10
μ
F capacitor
begins to charge.
Notes:
EXPERIMENT #18: LIGHT DIMMER
Wiring Sequence:
o
18-19-20-48
o
25-116-124
o
46-115-90
o
119-47-131
o
89-132
o
121-122
Schematic
Summary of Contents for EP-130
Page 11: ... 11 I ENTERTAINMENT CIRCUITS ...
Page 26: ... 26 II BASIC SEMICONDUCTOR AND COMPONENTS CIRCUITS ...
Page 36: ... 36 III LED DIGITAL DISPLAY CIRCUITS ...
Page 41: ... 41 IV A TOUR THROUGH DIGITAL CIRCUITS ...
Page 49: ... 49 V MORE ADVENTURES WITH DIGITAL CIRCUITS ...
Page 64: ... 64 VI THE WORLD OF TRANSISTOR TRANSISTOR LOGIC ...
Page 77: ... 77 VII APPLICATION CIRCUITS BASED ON THE OSCILLATOR ...
Page 88: ... 88 VIII BASIC OPERATIONAL AMPLIFIER CIRCUITS ...
Page 116: ... 116 IX MORE ADVENTURES WITH OPERATIONAL AMPLIFIERS ...
Page 129: ... 129 X COMMUNICATION CIRCUITS ...