Elenco Electronics EP-130, Manual

Page: 108 / 160

Now we’re going to make a winking LED circuit
using a dual operational amplifier. In this circuit, an
LED continues to light and turn off slowly.
Slide the switch to position B and connect the wires
for this circuit. When you finish assembling the
project, slide the switch to position A to turn on the
power. After a few seconds, you’ll see the LED start
to blink. Watch carefully and you should be able to
see that its on and off periods are about equal.
The dual operational amplifier works as an astable
multivibrator of a low frequency. You can change the
period of oscillation, that is, the LED blinking rate, by
using different values for R and C. See what
happens to the blinking rate when you change the
value of R to 220k
Ω
.
One last thing - the dual operational amplifier has a
high input impedance - resistance to input - so it
loses very little input current. This means you can
use it to build accurate blinkers and timers with
longer intervals.
Notes:
EXPERIMENT #89: OPERATIONAL AMPLIFIER WINKING LED
Schematic
-108-
Wiring Sequence:
o
81-31-63-131
o
33-67-90-94
o
93-68-113
o
69-82-84-89
o
83-70-114-121
o
119-124
o
122-132