28128 Parallax Inc, 28128 Datasheet - Page 79

• 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

This being the case, why doesn't everybody use resistive ladder networks for A/D and
D/A conversion? The resistive ladder network is also used in many A/D and D/A
integrated circuits, such as the ADC0831. The resistors used in integrated circuits are
microscopic implants on the surface of a silicon wafer. One advantage of IC converters is
that they have a high degree of accuracy. Another advantage an IC has is extra built in
circuitry similar to the voltage follower we built in Chapter #1
Build It
Build the circuit as shown in Figure 4-2. Pay careful attention to the values of the
resistors as well as what each resistor connects to. If your circuit from Chapter #3 is still
intact, just remove the potentiometer and build the resistive ladder network near the
sockets for pins P4 through P7. The input lead to the DVM, which was connected to the
wiper terminal on the potentiometer, should now be connected to the output of the D/A
converter. Be sure to pay close attention so that the resistors don't touch each other except
where they're supposed to on the breadboard nodes.
P7
P6
P5
P4
2
2
2
2
kΩ
kΩ
kΩ
kΩ
Vss
DAC Output
1
1
1
2
kΩ
kΩ
kΩ
kΩ
Vss
2
kΩ
Figure 4-1
Resistive Ladder D/A Converter.
This resistive ladder network can be used as a
D/A converter. The binary number input is sent
in parallel as 4-bits across 4 separate data
lines, P4 through P7. As long as the value of all
four bits are present at the same time, the
output of the D/A converter output will be the
intended discrete voltage value.