Transcript Output Devices

Simple Output Devices
TASK
1. Collect a set of Output Device cards.
2. Match each symbol to the correct name, energy change and
type (digital or analogue).
3. Get it checked.
4. Complete the following table with the correct information:
Symbol
Name
Energy
Change
Device
Type
Symbol
Name
bulb
M
Energy Change
electrical
Device Type
light
analogue
motor
electrical
kinetic
analogue
buzzer
electrical
sound
digital
solenoid
electrical
kinetic
digital
Symbol
Name
Energy Change
Device Type
loudspeaker
electrical
sound
analogue
relay
electrical
kinetic
digital
Relay Switch
A relay is a switch controlled by an electromagnet.
A coil of wire:
• carrying a current = magnet
• with no current = non magnet
Symbol:
Relay
Example of Relay Use
A high voltage mains motor is switched on when switch S is closed.
The small current in the 9V circuit makes the electromagnet become
magnetic.
This closes the switch and starts the motor.
S
9V
Relay
230 V
a.c.
M
Reed Relay
The reed relay uses a permanent magnet to open or close a switch.
This type of relay is used in burglar alarm systems to detect when
a door is opened.
Experiment
When the door is closed the magnet is close to the reed relay and
switch S is open.
When the door is opened, the magnet moves away from the relay,
causing switch S to close setting off the alarm.
magnet
S
::
..
::
..
to alarm
Solenoid
A solenoid is a coil of wire surrounding a metal rod.
It is an electromagnetic device that moves a metal rod backwards
and forwards.
Examples of Solenoid Use
• car central locking
• safe locks
• steering on radio controlled cars
• railway points
Light Emitting Diode (LED)
LED
Symbol:
Energy Change:
electrical
light
Type:
digital output device (only ON or OFF).
Wiring up an LED
An LED only conducts when it is connected the proper way around in a
circuit.
electrons
flow into
point of
triangle to
light LED
resistor in
series
LED lights
LED does not light
(FORWARD BIAS)
(REVERSED BIAS)
An LED is damaged if too large a current passes through.
***
A series resistor limits the size of the current,
protecting the LED from damage.
***
Q1.
(a)
Which LED’s in the following circuits will light?
LED 1
LED 3
LED 2
R
R
R
R
LED 4
(b)
What is the purpose of the resistor R in the above
circuits?
protect the LED from damage
(c)
When an LED lights it is said to be
LED’s
(d)
1 and 3
forward
biased.
are wired this way.
When an LED does not light it is
reverse
biased.
Calculating Size of Resistor
The resistor and LED are in series.
So the voltage across the resistor and the voltage across the LED
must add up to give the supply voltage.
VS
VR
VR + VLED = VSUPPLY
VLED
** not on data sheet **
0 V
Example 1
An LED can withstand a maximum current of 20 mA at 2 volts.
Calculate the minimum value of resistor required when the LED is
connected to a 5 V supply.
V IR
V
÷
I
R
R
x
VLED  2 V
VR  5  2
 3V
I  20 mA
 20  10 -3 A
R?
VR
R
I
3

20  10 -3
R  150 Ω
V
I
Example 2
An LED can take a maximum current of 18 mA at 2.2 V.
Calculate the minimum value of resistor required to protect the LED
when it is connected to a 6V supply.
VLED  2.2 V
VR  6  2.2
 3.8 V
I  18 mA
 18  10 -3 A
R?
R

VR
I
3.8
18  10 -3
R  211 Ω
Q1.
The maximum voltage allowed across an LED is 2.3 V and the
current through it must not exceed 10 mA.
The LED is connected to a 5 V supply.
Calculate the value of the resistor R connected in series with
the LED.
270 Ω
Q2.
An LED takes 10 mA and 1.5 V to work properly.
What value of series resistor is required if a 6 V battery is
used.
450 Ω
Q3.
An LED and resistor are connected in series to a 9 V supply.
The maximum voltage across the LED is 1.8 V and the current
through the LED must not exceed 12 mA.
Calculate the value of resistor required to protect the LED.
600 Ω
7 Segment Display
7 rectangular LED’s are arranged as follows to give a 7-segment
display.
a
f
e
b
g
The number 3 is
displayed by lighting
segments a, b, c, d and g
c
d
Energy Change:
electrical
light
Type:
digital output device (segment ON or OFF).
Experiment 1 – Making Numbers
Using a 7-segment display, display each number from 0 – 9 in turn
completing the table below.
Digit
Segments Lit
0
abcdef
1
bc
2
abged
3
abcdg
4
fgbc
5
afgcd
6
afedcg
7
abc
8
abcdefg
9
abcfg
Experiment 2 - Making Letters
Make as many letters as you can on the 7-segment display completing
the following table.
Letter
A
Appearance
Segments Used
abcefg
Which Output Device?
Selecting Output Devices
Here is a list of output devices:
buzzer, lamp, motor, relay, solenoid
Which output device could be used to:
(a)
indicate required cooking time for oven is complete
(b)
move conveyor belt at supermarket
(c)
stop and start movement of conveyor belt at supermarket.
buzzer
motor
relay
Q1.
Give a suitable output device for each of the following
situations:
(a)
an audible warning when an incubator become
too hot or cold
buzzer
(b)
a power on indicator for a stereo
(c)
switch on a high current circuit using a small
relay
current
(d)
indicator of which TV channel is selected
(e)
to push chosen sweets to hatch in a vending
solenoid
machine
(f)
run a conveyor belt around a bottling factory.
LED
7-seg.
motor
Binary Numbers
just in same way
as we represent
decimlas by
Binary numbers consist of a series of 0’s and 1’s.
Consider the binary number 1101.
continue to
increase
(double)
8
4
2
HTU
1
789
1 1 0 1
means 1 lot of 1
means 1 lot of 8
means no lots of 2
means 1 lot of 4
So we have as a decimal number: 8 + 4 + 0 + 1 = 13
** You must know the binary for numbers from 0 to 9 **
Decimal
Binary
8
4
2
1
0
0
0
0
0
1
0
0
0
1
2
0
0
1
0
3
0
0
1
1
4
0
1
0
0
5
0
1
0
1
6
0
1
1
0
7
0
1
1
1
8
1
0
0
0
9
1
0
0
1
Q1.
Q2.
Copy and complete the table of decimal and binary numbers:
Decimal
Binary
2
0010
7
0111
15
1111
18
10010
23
10111
What decimal number is represented by the binary number:
(a)
0100
4
(b)
1001
9
Relay