122-28176 Parallax Inc, 122-28176 Datasheet - Page 88

• 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

Challenge 3-7: Wiring a Relay
The relay can use high voltage, AC or DC, to energize a solenoid that closes or opens
electrically isolated mechanical contacts that can be used as input to the BASIC Stamp.
Signal conditioning these contacts is similar to the use of pull-up or pull-down resistors.
CONCLUSION
When acting as inputs, the BASIC Stamp typically senses a digital HIGH value for any
voltage above approximately 1.4 V and a digital LOW below 1.4 V. An input to the
BASIC Stamp does not necessarily need to be 5 V or 0 V, but must at least cross this
threshold voltage. Input voltages above 6 V will damage the BASIC Stamp.
BASIC Stamp inputs are uncommitted. That is, they are neither HIGH nor LOW without
an input committing them to the positive voltage or down to ground respectively. Most
mechanical switches require a pull-up or pull-down resistor for an Active-Low or Active-
High configuration respectively. Mechanical and electronic switches often require proper
conditioning.
Bipolar Junction Transistors (BJT) are current controlled devices that can operate as
current amplifiers or electronic switches. The base current controls the current in the
collector. With no base current, the transistor will be cutoff and act as an open switch.
With sufficient base current, the transistor's collector current will be at saturation, and the
transistor will act as a closed switch. The saturation current is a function of the supply
√
Wire the contacts (by drawing) in Figure 3-20 so the BASIC Stamp senses a
HIGH when S1 is closed, which energizes the solenoid and magnetically opens
the normally closed relay contacts labeled K1.
Figure 3-24
Sensing 115 V with a
Relay
(Drawing to be
completed by
student – do not
build)