28123 Parallax Inc, 28123 Datasheet - Page 329

• 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

Let’s say you turned two LEDs on at the same time. That means that inside the BASIC
Stamp, it is supplying the circuits as shown in Figure F-4. Have we exceeded the 20 mA
limit? Let’s find out. Remember that the simplified version of Kirchoff’s Current Law
says that the total current drawn from the supply equals the current supplied to all the
circuits. That means that I in Figure F-4 has to equal the total of the two currents being
drawn. Simply add the two current draws, and you’ll get an answer of 14.5 mA. You are
still under the 20 mA limit, so your circuit is a safe design.
7.23 mA
Yes, it’s true ! 1 A = 1 V/Ω (One amp is one volt per ohm).
Vss
3.4 V
+
-
470
LED
Ω
Vdd
I X
7.23 mA
470
I = ?
Ω
Vss
470
V
3
I
I
I
I
I
4 .
=
=
=
=
=
=
LED
Ω
V
. 0
. 0
1000
. 7
470
. 7
I
3
=
00723
00723
23
4 .
×
23
I
V
R
Ω
mA
×
A
470
I
I
I
V
A
=
=
=
Ω
Ω
14
. 7
I
1
23
5 .
+
I
mA
mA
Figure F-3
Current through
the Resistor
2
+
+
...
. 7
I
i
23
mA
Figure F-4
Total Current
Supplied to
Two LED
Circuits