28128 Parallax Inc, 28128 Datasheet - Page 137

• 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

The photoresistor senses light level. Under a bright light, the resistance can drop to as
low as a few ohms. In darkness, the resistance can climb as high as 50 k s. Figure 7-4
shows the circuit symbol for a photoresistor and a drawing of the component
Build It
Build the circuit shown in Figure 7-5. Recall from Chapter #4 that the inputs of the
ADC0831 have very high resistance, and they resemble an open circuit. Because of this,
it's okay to connect the output of the D/A converter to the ADC0831's Vin(+) input
without the buffer.
We are going to use the
conversion. Then we'll measure the voltage using the ADC0831 as a DVM.
P8
10 k
Ω
Vss
1 µF
Vss
PWM
2
4
3
command to send pulses to the RC circuit for D/A
Vdd
Vin(+)
GND
Vin(-)
ADC0831
8
Vdd
Vref
CLK
5
/CS
D0
1
7
6
Figure 7-4
Photoresistor Circuit
Symbol and Component
P0
P1
P2
Figure 7-5
RC Circuit for PWM D/A
Conversion
Connected to the Vin(+)
terminal of the ADC0831.
The ADC0831 is
connected to the output of
the D/A converter to
measure the output
voltages.