28123 Parallax Inc, 28123 Datasheet - Page 328

• Manufacturer Part Number: 28123
• Description: TEXT WHAT'S A MICROCONTROLLER
• Manufacturer: Parallax Inc
• Type: Programmingr

Specifications of 28123

• Style: Book
• Title: What's a Microcontroller?
• Contents: Whats a Microcontroller? Text
• Product: Microcontroller Accessories
• Core Processor: PIC16C57c
• Flash: 128 Bytes
• Operating Supply Voltage: 9 V
• Board Size: 31 mm x 16 mm
• Lead Free Status / RoHS Status: Not applicable / Not applicable

Figure F-3 shows an example of how to calculate the current the circuit uses if the
resistor is 470 Ω. Start with Ohm’s Law. You know the answers to V (3.4 V) and R
(470 Ω). Now, all you have to do is solve for I (the current).
Kilo is metric for 1000. The metric way of saying 1000 is kilo, and it’s abbreviated with the
lower-case k. Instead of writing 1000 Ω, you can write 1 kΩ. Either way, it’s pronounced
one-kilo-ohm. Likewise, 2000 Ω is written 2 kΩ.
Milli is metric for 1/1000, and it is abbreviated with a lower-case m. If the BASIC Stamp
supplies an LED circuit with 3.4 thousandths of an amp, that’s 3.4 milliamps, or 3.4 mA.
What’s a mA? Pronounced milliamp, it’s the notation for one-one-thousandth-of-an-amp.
The ‘m’ in mA is the metric notation for milli, which stands for 1/1000. The ‘A’ in mA stands
for amps. Put the two together, and you have milliamps, and it’s very useful for describing
the amount of current drawn by the BASIC Stamp and the circuits connected to it.
How much current is 7.23 mA? It’s the amount of current the LED shown on the right side
of Figure F-3 conducts. You can replace the 470 Ω resistor with a 220 Ω resistor, and the
circuit will conduct 15.5 mA, and the LED will glow more brightly. If you use a 1000 Ω
resistor, the circuit will conduct 3.4 mA, and the LED will glow less brightly. A 2000 Ω
resistor will cause the LED to glow less brightly still, and the current will be 1.7 mA.
5 V
+
-
Vdd
Vss
V = ? V
1.6 V
+
-
+
-
R
V
V
V
R
R
R
+
=
=
1
5
3
6 .
V
4 .
V
V
−
=
1
6 .
5
V
V
Figure F-2
Voltage Across
the Circuit,
Resistor, and
LED