Transcript revision all

SI Units
Mega
kilo
Units
milli
micro
nano
Pico
1000,000
1000
1x106
1x103
0.001
1x10-3
0.000,001
1x10-6
0.000,000,001 1x10-9
0.000,000,000,001
1x10-12
M
k
Ohms
Ohms
m
μ
n
p
Amps
Farads
Farads
Farads
p
n
μ
m 1
k
M
-12
-9
-6
-3
+3
+6
0
SI Units
Some shortcuts
k x m = cancel out
M x μ = cancel out
Kxμ=m
1/k = m
1/M = μ
M/k = k
k/m = M
am x an = am+n
am / an = am-n
Worked Examples
What current flows through a 1MΩ Resistor when
a voltage of 9V is applied across it?
I
=
=
=
=
=
V/R
9V/1MΩ
9/(1x106) Amps
9 x 10-6 Amps
9 μA
am x an = am+n
am / an = am-n
Worked Examples
What is the time constant for an RC network of a
220μf capacitor and 3k3 resistor?
t
=
=
=
=
=
CxR
220μf x 3k3
220x3.3 x (10-6x103)
726 x (10-3)
0.73s
am x an = am+n
am / an = am-n
Practice Questions
a)R=180kΩ
V=9V
b)R=3M3ΩV=6V
I=?
c)R=100Ω
V=3V
d)R=1MΩ
C=220μf
e)R=56kΩ
C=330pf
f) R=390kΩ
C=1000μf
I = V/R
I=? 0.05mA
1.82μA
I=? 30mA
t=? 220s
t=? 18.5ms
t=? 390s
t = CxR
Practice Questions
I=V/R
= 9 / 180k
= 9 / 180 x 10-3
= 0.05 x 10-3
= 0.05mA
I=V/R
= 6 / 3M3
= 6 / 3.3 x 10-6
= 1.82 x 10-6
= 1.82 μA
I=V/R
= 3 / 100
= 0.03A
= 30mA
t = CxR
= 220μf x 1M
= 220 x 1 x (10-6x106)
= 220 x (100)
= 220s
t = CxR
= 330pf x 56k
= 330 x 56 x (10-12x103)
= 18480 x (10-9)
= 18.5 x(10-6)
= 18.5 μs
t = CxR
= 1000μf x 390k
= 1000 x 390 x (10-6x103)
= 390000 x (10-3)
= 390 x (103x10-3)
= 390s
Resistors in Series
R total = R1 + R2 + etc
Resistors in Parallel
Two Resistors
R total = R1 x R2 = Product
R1 + R2
Sum
Three or more Resistors
1 = 1 + 1 + 1 etc
R total R1 R2
R3
Resistors
Resistors
a) Rtotal = 100+100=200
c)
b) Rtotal = 100x100 = 10,000 = 50
100+100
200
1 =
Rtotal
1 =
Rtotal
1 + 1 + 1
100
100
100
3
100
Rtotal = 100 = 33.3
3
Ohms Law
Worked Examples
What current flows through a 1MΩ Resistor when
a voltage of 9V is applied across it?
I
=
=
=
=
=
V/R
9V/1MΩ
9/(1x106) Amps
9 x 10-6 Amps
9 μA
am x an = am+n
am / an = am-n
Voltage Divider
Vout =
R2
x Vsupply
R1+R2
When resistors are in series
voltage is split in the same ratio
as the resistance.
A voltage divider uses this to give
a specified output (Vs). This
equates to the value of R2
divided by the total resistance,
times by the supply voltage.
Worked Example, V=9V, R1=3k3, R2=6k9
Worked Example
(In the exam, copy out the equation first)
Vs =
6k9
x 9V
(3k3 + 6k9)
=
6,900 x 9V
10,200
=
6.08 V
Copy down these formulae:
Two Resistors
R total = R1 x R2 = Product
R1 + R2
Sum
Vout =
R2
x Vsupply
R1+R2
200
100
Rt = R1 + R2
= 470 + 2k2
= 470 + 2200
= 2670
= 2k67 ohms
Vs =
200
x 9V
(200 + 100)
= 200 x 9V
300
= 6V
1k
Rt = R1 x R2
R1 + R2
2k2
= 1k x 2k2
1k + 2k2
= 2.2 x k
3.2
R = 100
I = 0.5A
V = 50V
V = 9v
I = 1mA
R = 9M ohm
= 2k2
3k2
= 0.687k
= 687ohms
9v
9v
200
2k2
3v
3v
100
470
Capacitors
Capacitance = Farads
Capacitor Charging
Volts
Capacitors store and hold
electric charge
++
++
++
++
++
++
++
++
Time
Keywords:
Electrolytic, nonelectrolytic, metal plates
separated by dielectric,
Capacitor Charging
Volts
++
++
++
++
t=RC
Time constant – the rate at
which a capacitor charges
through a resistor
++
++
++
++
Time
After one time constant,
capacitor is at 0.6 of its
full charge, and fully
charged after 5 time
constants
Capacitor Discharging
Volts
Time
t=RC
Time constant – the rate at which a
capacitor discharges through a resistor
Transistor as a switch
In order to switch on the
transistor the voltage at
the base must be 1.2V or
above
Sensors
Ω
Ω
Sensors
Voltage Dividers as Sensors
Vout =
R2
x Vsupply
R1+R2
So, if R2 >> R1, Vout is close to Vsupply
Transistor plus sensor (voltage divider)
Vout =
R2
x Vsupply
R1+R2
In cold
Vbase = 1/11 x 9V
= 0.81V
Transistor is off, bulb off
In warm
Vbase =2/12 x 9V
=1.5V
Transistor on, bulb on
System Diagram
Systems Electronics
input
process
output
Systems Electronics
input
Switch
LDR
Thermistor
Moisture Sensor
Variable Resistor
Microphone
Piezo
process
Transistor
Delay
Oscillator
Counter
Latch
Amplifier
Comparator
Logic Gates
PIC
output
Buzzer
Speaker
Bulb
LED
Motor
Relay
Solenoid
Piezo
Transistor Amplifier
Ice
ib
The current entering the base
controls the current that flows
through the collector and emitter,
with a fixed relationship called the
gain (hfe)
Gain (hfe)
Or Ib x Gain
Eg
= Ice
Ib
= Ice
Gain 100, Ib 1ma
Ice
=
?
Thyristor Latch
Similar to a transistor, but here a
signal/current at the gate latches the
thyristor on for as long as current flows
through it, interrupting this resets it to
off.
[once ON, it stays on until reset:
e.g. car alarm]
741 Op-Amp
IC = integrated circuit
DIL = Dual in line
741 op amp = 8 pin DIL IC
OP AMP as a comparator—the OP AMP compares the inverting input
voltage to the non-inverting input voltage, and gives a HIGH or LOW
output depending upon which is the greater input voltage.
The OP AMP detects very small changes in voltage multiplies the
difference by the GAIN (typically 100,000). Because the output is
HIGH or LOW, it is used as an analogue to digital converter (ADC) so is
suitable for connecting analogue sensors (E.g LDR, THERMISTOR) to
logic circuits.
Croc Clips link – LDR circuit
555 timers
IC = integrated circuit
DIL = Dual in line
555 timer = 8 pin DIL IC
ICs have three big advantages over conventional
circuits with discrete components:
• they take up very little space
• they are extremely reliable, and
• they are extremely cheap to make
8
1
4
555 timers - MONOSTABLE
RC timing:
t=RC
R
C
Recognising it = pins 6 and 7 are connected, through
R to +V
PIN 3 = output pin
t (seconds)
R (resistance)
C (capacitance)
Careful with units!!!
Monostable state = pin 2
high, pin 3 low
Pin 2 then triggered
(taken low), so pin 3 goes
high for the timing
period, then goes low.
[10k pull-up resistor
keeps pin 2 high]
555 timers - ASTABLE
C1 charges through R1 and R2,
until voltage across C1 is > 2/3
supply voltage. At this point pin
3 goes from high to low.
C1 then discharges into pin 7,
until voltage across C1 is < 1/3
supply voltage. At this point pin
3 goes from low to high.
Recognising it = pins 6 and 2 are connected, through
C to 0V
PIN 3 = output pin
Pin 3 = low = current flows into it
(sinking current)
Pin 3 = high = current flows out
(sourcing current)
Mark (time on) = 0.7 x (R1 + R2) x C1
Space (time off) = 0.7 x R1 x C1
NAND gate – ASTABLE
IC = 4011
R and C control frequency
Variable R = adjustment
Typically C is small (say 100nF)
And R is large (1M)
NAND gate – MONOSTABLE
IC = 4528
NAND gates with inputs connected –
operating as inverters
Timing depends on C, when the voltage
across C reaches a threshold level
(say 2/3rds of supply) the logic level
switches from O to 1
Counters
4017 and 4026
data
Some positives…
can you say YES to these…
Last years group achieved average 81% in their coursework, and 83% A*-C overall
YOU have achieved average 81% in their coursework
WE have nearly at the end of the revision and course
YOU already know enough to achieve A* - C overall
This morning YOU will know what to expect in next months exam,
and know what to do to perform your best
This morning we will study the remaining OUTPUT components and LOGIC
Outputs: relays + motors
Relay – small current
through the coil causes
magnetic field that moves
an armature that switches
ON the relay – keeps low
and high current systems
apart
The current
output from a
4017 won’t drive
a motor (too
small) – use a
transistor or
Darlington pair
to drive a motor
Switch bounce
Use a 555 monostable with ~ 1s delay
to clean the input
Use a SCHMITT TRIGGER
Circuit diagram link
Analogue and Digital Electronics
Analogue signals are constantly variable,
for example temperature, light intensity,
sound waves etc
Digital Electronics converts signals into
numerical values, using the binary number
system based on 1’s and 0’s (on and off)
Advantages of Digital
•Can be more reliably reproduced and
transmitted
•Can be processed
Binary Numbers
A single binary number is called a bit
An 8 digit binary number is called a byte, and can represent a decimal number
from 0 to 255
128s
64s
32s
16s
8s
4s
2s
units
decimal
1
0
1
0
1
0
1
0
170
0
0
0
0
1
1
1
1
15
0
1
1
1
1
1
1
1
127
1
1
1
1
1
1
1
1
255
Binary Numbers
Logic Gates
A Q
0 1
1 0
A
0
0
1
1
B
0
1
0
1
Q
0
1
1
1
A
0
0
1
1
B
0
1
0
1
Q
0
0
0
1
Logic Gates
A
0
0
1
1
B
0
1
0
1
Q
0
1
1
1
A
0
0
1
1
B
0
1
0
1
Q
1
0
0
0
A
0
0
1
1
B
0
1
0
1
Q
0
0
0
1
A
0
0
1
1
B
0
1
0
1
Q
1
1
1
0
Logic Gates
A
0
0
1
1
B
0
1
0
1
Q
0
1
1
0
A
0
0
1
1
B
0
1
0
1
Q
1
0
0
1
Logic Gates
A Q
0 1
1 0
A
0
0
1
1
B
0
1
0
1
Q
0
1
1
1
A
0
0
1
1
B
0
1
0
1
Q
0
0
0
1
A
0
0
1
1
B
0
1
0
1
Q
1
0
0
0
A
0
0
1
1
B
0
1
0
1
Q
1
1
1
0
A
0
0
1
1
B
0
1
0
1
Q
0
1
1
0
A
0
0
1
1
B
0
1
0
1
Q
1
0
0
1
Using Logic Gates
Inputs
Outputs
Switch in Gatehouse A
Motor (on barrier raised, off
Switch under barrier (on when barrier barrier lowered)
closed) B
Red Light
Switch (pressure pad) before barrier
Green Light
on road C
Switch (pressure pad) under barrier D
Switch (pressure pad) after barrier on
road E
Design using Logic Gates systems to;
- show a green light when the barrier
opens and red when closes
- automatically open the gate when the
car approaches, then close it when it has
passed
- allow the gatehouse switch to close the
gate unless a car is under it.
PIC Chips
Programmable Integrated Circuits
Come in various numbers of pins which limit the number of inputs and outputs
Easiest way to imagine a pic is like a programmable ‘process block’
Writing Programmes
Programmes can be written as flow charts
Start/End
Flashing Light
Input 1
On?
Process
o/p 1 on
Decision
Output
Wait 1
o/p 1 off
Wait 1
Circuit modelling and CAD CAM
Breadboard = know how these are configured.
You might get a “complete the connections” or a
fault finding question
Advantages = test the components you will
use, test in read conditions, can change
component values and test very quickly
Disadvantages = tricky to fault find, risk of
damaging components
Circuit modelling and CAD CAM
CAD = computer aided design
Advantages = quick to model a circuit, voltages and
currents can be measured, no damage to components,
design can be exported into a PCB layout design
program, use of programmable chips (PICs)
Disadvantages = unable to test the circuit in real
conditions so you have to make a pcb to test it
properly, software can be expensive
CAM
CAM = computer aided manufacture
• CNC processes to cut and drill PCB’s
• pick and place components automatically
• digital photography to check (QC)
component positions
• automated processes e.g wave soldering
PCB making:
http://www.youtube.com/watch?v=SKccLhFf1DY
http://vixy.net/
Or this
SAMPLE QUESTION – think like a computer…