28129 Parallax Inc, 28129 Datasheet - Page 119
![TEXT BASIC ANALOG & DIGITAL](/photos/6/49/64954/mfg_28129_sml.jpg)
28129
Manufacturer Part Number
28129
Description
TEXT BASIC ANALOG & DIGITAL
Manufacturer
Parallax Inc
Type
Programmingr
Datasheet
1.28129.pdf
(176 pages)
Specifications of 28129
Style
Book
Title
Basic Analog and Digital
Contents
Basic Analog and Digital Text
Product
Microcontroller Accessories
Lead Free Status / RoHS Status
Not applicable / Not applicable
- Current page: 119 of 176
- Download datasheet (3Mb)
100 k
POT A
Build It
The circuit in Figure 6-4 is called "astable multivibrator" and is used to generate a steady
stream of pulses. The 555 timer's output drives a piezoelectric speaker circuit and it uses
two potentiometers as variable resistors. This allows control the pulse width and duty
cycle, of the output.
Build the circuit shown in Figure 6-4. Note that there is a lower case "nc" below two
potentiometer terminals in the figure. This stands for "not connected". Since the
potentiometer is used as a single variable resistor instead of a voltage divider, the third
terminal doesn't get connected to anything. It's OK to plug the nc terminal into a row on
the breadboard; just don't plug anything else into the same row.
Ω
Vdd
nc
100 k
POT B
Ω
2
nc
555 Timer
1
4
3
8
10 µF
7
6
7
6
2
555 Timer
2
3
4
1
Vdd
Vss
555 Timer
GND
Trig
Out
Res
8
1
Thres
Con
Vcc
Dis
4
3
8
7
6
5
Figure 6-3
Symbol and pin map
for 555 Timer
As always, make
sure to locate the
index mark when you
place the part on the
breadboard.
P0
Figure 6-4
Astable
Multivibrator
circuit
With
adjustable
high and low
times.
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