28122 Parallax Inc, 28122 Datasheet - Page 83

• Manufacturer Part Number: 28122
• Description: KIT WHAT'S A MICRO:PARTS ONLY
• Manufacturer: Parallax Inc

Specifications of 28122

• Accessory Type: Parts Kit
• Product: Microcontroller Accessories
• Core Processor: PIC16C57c
• Flash: 128 Bytes
• Operating Supply Voltage: 9 V
• Board Size: 31 mm x 16 mm
• For Use With/related Products: Board of Education Full Kit
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

How the Pushbutton Circuit Works
The left side of Figure 3-4 shows what happens when the pushbutton is not pressed. The
LED circuit is not connected to Vdd. It is an open circuit that cannot conduct current.
By pressing the pushbutton, you close the connection between the terminals with
conductive metal making a pathway for electrons to flow through the circuit.
Your Turn – A Short-Circuit
Figure 3-5 shows a different circuit that will cause the LED to behave differently. When
the button is not pressed, the LED stays on. When the button is pressed, the LED turns
off. The reason the LED turns off when the pushbutton is pressed is because current
always follows the path of least resistance. When the pushbutton is pressed, terminals
1,4 and 2,3, have almost no resistance between them, so all the current passes through the
pushbutton (short circuit) instead of the LED.
√
√
√
Current
Press and hold the pushbutton, and verify that the LED emits light while you
are holding the pushbutton down.
Build the circuit shown in Figure 3-5.
Repeat the tests you performed on the first pushbutton circuit you built with
this new circuit.
No
1, 4
2, 3
Vdd
Vss
470
LED
Ω
Current
1, 4
2, 3
Vdd
Vss
470
LED
Ω
Figure 3-4
Pushbutton Not
Pressed, and
Pressed
Pushbutton circuit
open (left) and
closed (right)