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Figure 2-5 shows what you will program the BASIC Stamp to do to the LED circuit.
Imagine that you have a 5 volt (5 V) battery. Although a 5 V battery is not common, the
Board of Education has a device called a voltage regulator that supplies the BASIC
Stamp with the equivalent of a 5 V battery. When you connect a circuit to Vss, it's like
connecting the circuit to the negative terminal of the 5 V battery. When you connect the
other end of the circuit to Vdd, it's like connecting it to the positive terminal of a 5 V
battery.
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+
Vdd
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N
N
N
+
+
+
+
+
+
+
5 V
+
=
N
+
+
+
-
-
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N
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_
Vss
N
N
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Volts is abbreviated V. That means 5 volts is abbreviated 5 V. When you apply voltage to
a circuit, it's like applying electrical pressure.
Current refers to the rate at which electrons pass through a circuit. You will often see
measurements of current expressed in amps, which is abbreviated A.
current an electric motor draws is often measured in amps, for example 2 A, 5 A, etc.
However, the currents you will use in the Board of Education are measured in thousandths
of an amp, or milliamps. For example, 10.3 mA passes through the circuit in Figure 2-5.
When these connections are made, 5 V of electrical pressure is applied to the circuit
causing electrons to flow through and the LED to emit light. As soon as you disconnect
the resistor lead from the battery's positive terminal, the current stops flowing, and the
LED stops emitting light. You can take it one step further by connecting the resistor lead
to Vss, which has the same result. This is the action you will program the BASIC Stamp
to do to make the LED turn on (emit light) and off (not emit light).
Chapter 2: Your Boe-Bot's Servo Motors · Page 49
+
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Vdd
N
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+
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+
5 V
+
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_
Vss
N
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Figure 2-5
BASIC Stamp
Switching
N
N
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+
+
+
+
+
-
The BASIC Stamp can
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be programmed to
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internally connect the
N
-
N
LED circuit's input to
Vdd or Vss.
The amount of
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