28128 Parallax Inc, 28128 Datasheet - Page 51

• 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

Chapter #3: Basic Analog to Digital Conversion
BUILD YOUR OWN DIGITAL DC VOLTMETER
A digital DC voltmeter (DC DVM) is a handy tool for measuring voltage between two
contact points. In this experiment, we will build a DVM for measuring DC voltage in the
0 to 5 volt range. A common use for a DC DVM is testing the voltage (potential) between
the two terminals on a battery.
A digital voltmeter is so named because it displays its measurements with digits. The
digits 0 through 9 and a decimal point are used to display the voltage measurements as
decimal values. The digits 0 and 1 could be used. It would still be a "digital" voltmeter,
but it would have binary display instead of a decimal display. Making sense out of each
measurement would be time consuming. Since our DVM processes its measurements in
binary, we'll start with a binary display and then modify it to the more conventional and
easy to read decimal display.
In Chapter #1, we used an LED circuit to display changes in analog voltage level applied
to a circuit. As a “continuously variable value”, analog voltage varies within a continuous
range. We'll use the potentiometer as we did in Chapter #1 to make a range of voltages
that can vary continuously between 0 and 5 volts on the Board of Education.
Although information about analog voltage can be processed efficiently with binary
devices, the voltage has to be sampled and described using binary numbers first. The
ADC0831 is a common integrated circuit that does this job. It describes the analog
information with binary numbers for devices that process binary information, such as the
BASIC Stamp.
In this experiment, we will make a DVM using the BASIC Stamp together with the
ADC0831 integrated circuit. A pot will be wired to the Board of Education and adjusted
to make analog output voltage. The DVM will then be used to measure samples from the
pot’s continuous range of voltage outputs.
Continuous range: A minimum value, a maximum value, and everything in between. When
a source of voltage varies over a continuous range, it is considered an analog voltage.
We will use our DVM to sample voltages over a continuous range, from 0 to 5 volts. So, the
voltage we measure might be 1.234 volts or 3.857564… volts, or 4.9999… volts, etc.