28128 Parallax Inc, 28128 Datasheet - Page 159

• 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

Under brighter light conditions, the resolution is poor. You can replace the 1 µF capacitor
with a 10 µF capacitor to increase the resolution at higher light levels. For full sun, some
kind of shade for the photoresistor would help. If you are dealing with low light
conditions, use a 0.1 µF capacitor instead.
The reason for using different capacitors is because the range of resistances for the
photoresistor varies for different ranges of light levels. Under lower lighting, the
photoresistor has a much higher range of resistance values than it does in a well-lit or full
sun area.
As discussed earlier, the discharge time depends on the RC time constant, R x C. If R
tends toward a relatively high range of resistances, using a smaller value of C will bring
the value of R multiplied by C back down. Likewise, if R is low, using a larger value of
C helps bring the value of RC back up.
Figure 8-8
Sample Debug
Terminal Output
in After
Somebody
Turned Out the
Lights