122-28176 Parallax Inc, 122-28176 Datasheet - Page 87

• Manufacturer Part Number: 122-28176
• Description: GUIDE STUDENT PROCESS CONTROL
• Manufacturer: Parallax Inc

Specifications of 122-28176

• Accessory Type: Manual
• Product: Microcontroller Accessories
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• For Use With/related Products: Propeller Education (PE) Kit
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Contains lead / RoHS non-compliant

Figure 3-23 (top): Higher-voltage digital signals can be interfaced using a 74HC4050
buffer or 74HC4049 inverter powered at +5 volts. These devices can safely handle inputs
up to 15 volts. Again, the grounds must be common.
Figure 3-23 (bottom): An opto-coupler may be used to interface different voltage levels
to the BASIC Stamp. The LED’s resistor holds current to a safe level while allowing
enough light to saturate the phototransistor. The input circuit can be totally isolated from
the phototransistor’s BASIC Stamp power supply because they do not need to share a
common-ground. This isolation provides effective protection of each circuit in case of an
electrical failure of the other.
The optical reflective switch will be explored further in Chapter 4.
Figure 3-23
Digital Interface
Circuits
Top: High
Voltage Logic to
BASIC Stamp
Bottom:
Optocoupler to
BASIC Stamp