28128 Parallax Inc, 28128 Datasheet - Page 93

• 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

Comparing the two tables, it should be fairly clear that the buffer (voltage follower)
eliminated a problem caused by connecting the LED circuit directly to the D/A
converter's output. The voltage of the D/A output without a buffer reached a maximum
well below the D/A converter's 3 volt maximum. On the other hand, the buffered output
went all the way to 3 volts with no problem.
P0
P1
P2
1
7
6
Vdd
/CS
CLK
D0
ADC0831
8
Vdd
Vref
5
Vin(+)
GND
Vin(-)
2
4
3
Figure 4-8 D/A Circuit With a Buffer
Vss
P7
P6
P5
P4
2
2
2
2
kΩ
kΩ
kΩ
kΩ
Vss
1
1
1
2
kΩ
kΩ
kΩ
kΩ
Vss
LM358
2
kΩ
Vdd
A
Vss
270
LED
Ω