28128 Parallax Inc, 28128 Datasheet - Page 119

• Manufacturer Part Number: 28128
• Description: KIT BASIC ANALOG/DIGI PARTS ONLY
• Manufacturer: Parallax Inc

Specifications of 28128

• Accessory Type: ADC, DAC
• Product: Microcontroller Accessories
• For Use With/related Products: BASIC Stamp® 2 and Board of Education
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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.