28119 Parallax Inc, 28119 Datasheet - Page 120

• Manufacturer Part Number: 28119
• Description: KIT UNDERSTANDING SIGNALS
• Manufacturer: Parallax Inc

Specifications of 28119

• Lead Free Status: Contains lead
• Accessory Type: Oscilloscope
• Interface Type: USB
• For Use With/related Products: BASIC Stamp® 2 and Board of Education
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

How healthy is your battery? We measured the clipped signals for 3 different 9 V
batteries, and had readings of 8.01 V, 7.29 V and a low of 6.53 V, shown in Figure 8-13.
ACTIVITY #2: INVERTING AMPLIFIER WITH ADJUSTABLE DC OFFSET
The op-amp circuit in this Activity performs two functions at once. The first function is
that of an inverting amplifier; the second supplies a DC offset to the output signal.
Recalling the formula Chapter 4, using a 10 kΩ resistor as Ri and a 20 kΩ resistor as Rf
will cause a gain of 2. Recall also that an in the case of an inverting amplifier, the
voltage output will be negative 2 times the voltage input. Therefore, an input signal that
swings from 1 to 3 V put through an inverting amplifier with a gain of 2 would output a
signal that swings from -2 to -6 V. Further, recall that an op-amp cannot output a signal
with a voltage that exceeds the voltages applied to the supply rails (Vcc and Vee). Notice
that in the schematic (Figure 8-14) that Vee is connected to 0 V. Since the whole range
of the output signal is below 0 V, the entire signal would be clipped, and would only be
visible on the OPTAscope as a 20 mV flat line!
Figure 8-13:
Output signal
with a gain of
3, heavily
clipped
Note that the
MAX voltage
measurement
shows 6.53 V,
evidence of a
weakening 9 V
battery.