Basic Electronics
I
V
OHM'S LAW
R
V=I * R
volts = amps * ohms
volts = mA * Kohms
I
I = V/R = 9V/1K = 9mA = .009A
resistor
I
1/R
V
LED
anode
I
~10 mA
cathode
+ 1.5 V -
I = ??
V 5  1.5
I 
 10.6 mA
R
330
ARDUINO CONTROL OF LED
ARDUINO
5V
0V
PIN 0
20 mA max
GND
digitalWrite(0,HIGH);
delay(1000);
digitalWrite(0,LOW);
ARDUINO
5V, 20 mA
PIN 0
DEVICE
GND
What if device needs more than 5V or
more than 20 mA??
Computer controlled switch
V big
DEVICE
STAMP
PIN 0
GND
I big
Transistor
current-controlled amplifier, current-controlled switch
BASE
COLLECTOR
I small
I big = b*I small
EMITTER
Think: spray can!
COLLECTOR
BASE
EMITTER
Ic = b*Ib
Ib
Ie = Ib + Ic
ONE-WAY!
5V
0V
ON
I
ON
I
OFF
V
OFF
Vce sat
0.1 – 2.0 V
V
LOAD: MOTOR, SOLENOID, RELAY, LAMP, …
TO-92
TO-220
2N3904
TIP120
100 mA
1-2 A
TO-3
20-50 A
Things to look for
on a data sheet
•
•
•
•
•
•
Max current, Ic max
Max volts, Vce max
Max power, P max
Vce sat
Gain, Hfe or b
Switching time
2N3904
TIP 120
Interfacing to Motors
Motor interface
FOR SMALL MOTOR, USE 2N3904
Pin 2
GND
-
+
Arduino pin limits
20 mA per PIN
40 mA TOTAL
10.6 mA
4.4 mA
1A
Hook motor straight to Arduino?
POWER
+
V
I
P=V*I
-
P = ??
I = V/R = 9/10 = 0.9 A
P = V*I = 9*.9 = 8.1 W
demo
I
P = 12 * I
HEAT
I, V
t, w
WOW! WHAT A
GREAT MOTOR I
GOT AT AX-MAN!
AND IT RUNS ON
12v!
Later…
YOUCH!!
IT'S HOT!
12
V
5. 0  0. 6
ib 
 4.4 mA
1000
5V
Ic
Ib
Vce sat ~ 2.0 V
Let Ic = 5 A
HOT
PWR = V*I = 2.0*5 = 10 W !!!
wasted
RELAYS
To control larger loads
Relays
• Electromagnet-controlled switch
• User for (1) larger loads, (2) bi-directional motor
COIL
COIL  control side
12V, 120 ohm, 100 mA
5V, 500 ohm, 10 mA
CONTACTS  load side
240 VAC/28 VDC, 10 A
100 VDC, 1A
120 VAC/24 VDC, 0.5 A/1.0A
CONTACTS
Types of relays
GENERAL PURPOSE
COIL: 12, 24 VDC; 120 VAC
CONTACTS: 5-10 A
REED
COIL: 5, 12 VDC
CONTACTS: .5-2 A
SOLID STATE
COIL: LOGIC INPUT
CONTACTS: 2-25 A
JAMECO 174431
COIL: 12 V, 400 OHM, I = V/R = 12/400 = 30 mA
CONTACT: 24 VDC, 15 A
Transistor drive for a relay
NOTE: RELAY COIL CAN SUCK CURRENT
SOLENOIDS
For linear, short-range, on-off motion
x
F
Force when
energized
MAX ON-TIME = ½ SEC
¼ in.
x
www.jameco.com
SPST
(NO, NC)
Switches
SPDT
#define MOTOR 0
#define SWITCH 4
.
.
.
digitalWrite(MOTOR,HIGH);
delay(1000); // wait for motor to clear switch
while (digitalRead(SWITCH)
;
digitalWrite(MOTOR,HIGH);.
.
.
WIRE
1. CONNECT POINTS OF EQUAL VOLTAGE
2. CARRY CURRENT
STRANDED
Flexible
SMALL WIRE
+
HIGH CURRENT
SOLID
Higher current
Type
Gauge
Max I
Notes
Wrap wire
30
200 mA
wrapping, signal level only
Hookup
24/22
1-2 A
general purpose
Lamp cord
18
5A
House wire
14/12
15/20 A
“CABLE” = multiconductor wire bundle
e.g. modular phone cord: 28g solid, 4 conductor
BATTERIES
• Primary
• Important specs
– Zinc
– Energy density
– Alkaline (most
– Voltage
common)
• Zinc/Alkaline: 1.5 V
– Lithium (camera,
• Lead Acid: 2.0 V
watch)
– cars: 6, 12 V
• Secondary
• NiCd: 1.2 V
(rechargeable)
– Power tools: 4.8, 6.0,
– Sealed lead acid (car)
7.2, 9.6, 12, 18 V
– Gel
– Maximum current
– NiCd
• “Cold-cranking amps”
– NiMH
– Capacity
– Lithium
• Amp-hours or mAHrs
Capacity and discharge
• 12 V (10 cell) NiCd pack
rated at 1300 mAH
– 1.3 Amps for 1 hour
– 520 mA for 2.5
hours…..in theory
• Top-notch cells for RC
racing can provide 2300
mAH
• 9V alkaline
– 580 mAH @ 12 mA (can
deliver 12 mA for 48 hrs)
100
Service life
Hrs
1
10
mA
100
Alkaline technology
9V
Discharge curve
t
See www.duracell.com (or other sites) for more
Battery technologies
Chemistry
NiCd
Energy density Cell voltage
(W-H/Kg)
38
1.2
Lead Acid
40
2.0
NiMH
70
1.2
Carbon-Zinc
75
1.5
Alkaline
130
1.5
Lithium-Ion
130
3.7
Lithium-Poly
190
3.7
Lithium
300
3.0
www.hardingenergy.com