TKT-3500

Microcontroller

systems

Lec 7 – Hardware design part 1

Ville Kaseva

Department of Computer Systems

Tampere University of Technology

Fall 2010

#2/42

Sources

Original slides by Erno Salminen

Robert Reese, Microprocessors: From Assembly

to C with the PIC18Fxx2, Charles River Media,

2005

Northwestern University mechatronics design wiki

http://hades.mech.northwestern.edu/wiki/index.php/Mai

n_Page

Wikipedia

#3/42

Contents

Basic electronics

Current, voltage, power

Ohm’s law, Kirchoff’s law

Resistor, capacitance, inductance

Semiconductors: diode, transistor, IC

Others: fuse, regulator, op. amp.

Meters: multimeter, oscillator, signal analyzer

Packages and assembly

#4/42

Purpose

Not knowing exactly the background of the

attendants, here’s a brief reminder of basic

electronics

#5/42

Current I

Current measures how many charge carriers

(electrons) flow through a conductor

Conductor is material that can conduct electrical current,

usually some metal such as aluminum or copper

Symbol I; unit Ampere, A

microcontroller systems operate with e.g. 10 mA – 500 mA

Current may flow only in a closed circuit

from positive voltage to negative

Direct current (DC) flows always in one direction

whereas alternating current (AC) varies

The origin of current is also called source whereas

the destination is called sink or drain

#6/42

Voltage U/V

Voltage means electrical potential –

difference in amount electrical charge –

between two points of a circuit

Symbol U (sometimes V); unit Volt, V

microcontrollers use e.g. 2-5 V

Voltage source Vs is a device that provides

current with (ideally) fixed voltage level

single AA battery provides 1.5 V, car battery 12 V

wall outlet 230V, 50Hz alternating current (AC)

In practice, large current causes voltage drop

#7/42

Ohm’s law

The relation between voltage and current

U = R * I

Current I that flows through resistance R, causes

a voltage difference V

Or R = U/I, or I = U/R

Current causes voltage drop

Voltage difference causes current

VR

I

+

-Vs

RVs = VR = R * I

I = Vs / R

#8/42

Power P and energy E

Power measures the amount of work done in unit time Rate of energy consumption

Symbol P; unit Watt, W

Product of voltage and current: P = U * I = U * (U/R)

PIC uses <1 W of power

Energy E means the total work Symbol E; unit Joule, J

E = P * t = (U*I) *t, where t denotes time

Sometimes given in Watt-hours, Wh or volt-Ampere-hours VAh

Battery stores some amount of energy E that is spent at certain rate P One AA battery contains 1000-3000 mAh

#9/42

Kirchoff’s law

Electrical current

1. cannot disappear anywhere

2. cannot originate out of nowhere

More formally, sum of currents flowing into a

circuit node equals the sum of leaving

currents

Σ Ii = Σ Io

Current flows also in the ground wire

although its voltage is (almost) zero

so called ground loop

I1I2

Is= I1+ I2

Basic passive

components

#11/42

Resistance R

Property of a conductor defining the how much is

prevents the current from flowing

Symbol R; unit Ohm, Ω

1 Ω = 1V / 1A

Ideal conductor has R= 0 Ω

Ideal insulator has R= ∞ Ω

Passive component (does not need supply voltage to

operate)

Unpolarized – no matter which way you connect it

Basic microcontroller system utilizes resistors e.g. in

the range 50Ω -500 kΩ

Drawing symbols:

#12/42

Resistances in series

Current flows through all resistors – large

resistance

Rtot = Σ Ri

Voltage division so that sum of voltages

across resistors equals the source voltage

Vs = VR1 + VR2

Vs = I * Rtot

Vs = I * (R1 + R2)

VR2 = R2/Rtot * Vs

VR2

I

+

-Vs

R2

R1

VR1

#13/42

Resistances in parallel

Current has more paths – low resistance

Same voltage across all Ri

VR1 = VR2 = Vs

Rtot =

Is= Vs / Rtot

Current divider:

I1 = (R2 / Rtot) * Is

I2 = (R1 / Rtot) * Is

I1 I2

Is= I1+ I2

+

-Vs

VR1

1

+1 1R1 R2

VR2R2R1

Is

#14/42

Fuse

A fuse is just a thin wire, enclosed in a

casing, that plugs into the circuit so that all

charge flows through the fuse wire

If the current climbs too high, it burns up the

wire

Protects the circuit against excess current

due to, for example, a short-circuit

Fuse must be of right size

Does not burn accidentally

Will be burn before other circuitry

Size measured in tolerated amperes

#15/42

Capacitance C

Symbol C; unit Farad, F

Component is called capacitor (’kondensaattori’)

Commonly used capacitors are in picofarad range

Stores electrical charge into electrical field

Two metal plates very close to each other with

insulator in between

”Resists the change in voltage”

used for filtering and as a temporary voltage

source

Drawing symbols:

Basic, unpolarized Polarized

+

#16/42

Capacitance C (2)

Capacitors in parallel Ctot = Σ Ci

Capacitors in series Ctot = 1 / (Σ 1/Ci)

Current depends on the change in voltage

Does not conduct if voltage is stable

Voltage across the capacitor is integral of

current

i.e. how much charge have flown into the capcitor

i(t) = C dvdt

v(t) = i dt1

C

#17/42

Charging/discharging a capacitor

Large, abrupt voltage difference

when switch opens/closes

Large current immediately after

that

Current decays as C gets

charged/discharged

i(t)+

-Vs

R1

vC(t) vC(t)

t1a

Vs

CR2

t2at1b

switch1

switch2

0) both

switches

open

1) close

switch1

2) open

switch1

3) close

switch2

Charge C ”Hold” Discharge

i(t)

R1 > R2

time

time

#18/42

Capacitor for filtering

+

-vs

R1

vC(t)

C

switch1 v(t)

vs

time

vc

+

-vs

vo(t)

C

switch1 v(t)vs

time

vc

RC circuit filters high frequencies (sharp edges)

Capacitor does not conduct when voltage is

constant, i.e. it does not pass DC component

through. Hence, vo has Only the AC component.

#19/42

Inductance L

Symbol L; unit Henry, H

Commonly used inductors are in mH range

”Resists the change in current”

Coils are used for filtering

Stores electrical charge into magnetic field

Even when current is turned off, magnetic field

induces a current

This may create voltage spikes that cause noise

problems and may break other components

Inductors in series/parallel act like resistors

Drawing symbols:

#20/42

Inductance and magnetic field

Current flowing through

wire creates a magnetic

field around it

”Right-hand rule” gives

the direction of field

Magnetic fields sum

together in the ”core” of

the coil

Antennas are based on

induction phenomena

current

direction of

magnetic field

#21/42

Impedance

How much an electrical entity impedes (slows down) the flow of current

Symbol Z; unit Ohm, Ω

Same unit with resistance

Sum of resistance and reactance

Reactance is frequency-dependent part Applies to capacitors and coils

ZC = 1 /ωC = 1 / (2 * π * f * C)

ZL = ωL = 2 * π * f * L

On high frequency, impedance of C is low whereas impedance of L is high

#22/42

Input and output impedance

When voltage is applied to circuit’s inputs, a current will flow Input impedance defines its magnitude

In many cases, input resistance is accurate anough

When output circuit is closed, a current will flow Output voltage is not constant, Vout, loaded < Vout, open-circuit

Small load takes large current

Creating a short-circuit to outputs, defines the maximum Iand, hence, the circuits’ output resistance

Ideally, Zin=∞Ω and Rout = 0 Ω

circuit

internal

structur

e

Vin Vout

circuit

VinZin

Rout

Vout

Iin

Example circuit Equivalent circuit

Zload

Iout

VOC

#23/42

Basic passive filters

vo(t)

C

vi(t)

vo(t)Cvi(t)

Gain = Vout/Vin

freqeuncy

Gain = Vout/Vin

freqeuncy

1.0

1.0

f0

f0

Low-pass filter

In both cases f0 = 1 / ( 2 * π * RC)

High-pass filter

Exam

ple

uasge: push b

utton

#24/42

Basic passive filters (2)

vo(t)C Lvi(t)

vo(t)

C

Lvi(t)

Gain = Vout/Vin

frequency

Gain = Vout/Vin

frequency

1.0

1.0

f0

f0

Band-pass filter, at f0 the impedance Z → 0

In both cases f0 = 1 / ( 2 * π * LC)

Band-pass filter, at f0 the impedance Z → ∞

#25/42

Suodattajat

Yhden tuttavani tilatoverit ovat oudossa työssä. He suodattavat signaalia Nokialla. Tämä on totta, enkä edes valehtele! Niillä on siellä Nokiallaan FIR-suodattimia ja mediaanisuodattimia ja ties mitä astraalikotkotuksia ja aamulla ne alkavat suodattaa sitä signaalia ja kaiketi pelata sököä, (tai rakentaa Taj Mahalia tulitikuista) odottaessaan, että suodattimeen kertyisi jotain, töhkää kaiketi. Välillä joku ketterämpi veli käy kapistamassa suodattimesta lavuaariin kaiken roskan, mitä siihen on tarttunut, ja keittää kahvia ja sitten taas peli jatkuu (tai Taj Mahal rakentuu). Illalla signaali viedään haponkestävään holviin ja suodattimet pestään ja pannaan astiakaappiin. Suodattaminen jatkuu taas seuraavana päivänä, ellei ole viikonloppu tai pyhä. (Niiden työehtosopimuksen mukaan viikonloppuina ja pyhinä ei tarvitse suodattaa signaalia yhtään, mutta saa silti palkan aivan kuin suodattaisi.) Tyhmä luulisi, ettei työnantajaa voi kauan pettää ja suodattaa aina vaan samaa signaalia, mutta viisas arvaa, että kun näytteenottoa tarkennetaan, kohina jotenkin vaan lisääntyy ja voit suodattaa sitä samaa signaalia aina vaan, vaikka sata vuotta, eikä työnantaja älyä mitään filunkia!

Markus Kajo, Kettusen kolmas

Some semiconductor

devices

#27/42

Semiconductor devices

Semiconductor – material which conducts

varying electrical current depending on the

conditions, e.g. voltage or light

Diode

simplest semiconductor device, two terminals

conducts in one direction

Transistor

three-terminal devices

conductivity is controlled with one of the terminals

Integrated circuits

#28/42

Diode

Conducts current in one

direction only

Conducts only when forward

biased

Vanode - Vcathode > Vthreshold

Usually Vthreshold = 0.7 V

Often used for protecting other

circuitry

Also used for rectifying (AC to

DC)

symbol:

real component:

#29/42

Diode (2)

When voltage in forward direction rises above

threshold, the diodes R approaches zero

Current is limited by other circuitry

Diode causes constant

voltage drop, usually 0.7V

Voltage in backwards

direction, prevents

conduction

Unless diode breaks with

large voltage...

+

-Vs

Vd

Vd

I

#30/42

Some diode types

1. basic – most comon

2. light-emitting diode (LED) – produces light (infrared-visible-ultraviolet) relative to current laser diode – used e.g. optical

communication

3. photodiodes – conductivity depends on the luminance

4. Schottky – hysteresis prevents spurious changes of diode output

5. zener (and avalanche)– conduct backwards (see voltage regulators)

6. And many more...

symbol:

real component:

#31/42

#32/42

Diode usage for clamping

Clamping limits voltage into desired range

Useful when we need to protect circuits from high

voltages at their inputs

We specify the maximum and minimum voltage we

want by applying voltages across a diode.

If Vin > Vmax, diode D1 becomes forward biased and conducts, thus forcing Vout to stay at Vmax.

If Vin < Vmin, diode D2 conducts and prevents the Vout from dropping any lower

Often Vmax = Vdd, Vmin = GND

#33/42

Rectifying circuits

ACin

ACin

DC out

DC out

time

time

Direction of

current when

AC in is positive

Half-wave (above) and full-wave (right) rectifiers

loadCfilt

#34/42

Transistor

Amplifies or switches electronic signals

Sometimes considered as ”the greatest

invention of 20th century”

Three terminals

current in

current out

control terminal

The last defines the conductivity between the

two others

#35/42

Transistor (2)

Many different flavors Controlling quantity (current vs. voltage)

Control polarity: positive/negative

+ Depletion/enhancement type FETs

The polarity of terminals: doped with n-type or p-type

The main categories 1. bipolar junction transistor (BJT): current-controlled

2. field-effect transistor (FET): voltage-controlled

we won’t go into details...

gate

drain

source

base

collector

emitter

Slightly different

symbols and naming of

terminals

VGS

BJTFET

IB

II

drain = nielu

gate = hila

source = lähde

IB ≈0

0.7V

#36/42

Transistor (3)

a) Transistor off – not conducting – when

control voltage (or current) is zero

b) Transistor on – starts conducting – when

control voltage increases

1. Conductivity increases with control

2. When control increases enough, transistor

becomes saturated – it cannot conduct more

current

When conducting, base-emitter voltage (or

gate-source) is constant

Similar p-n junction as in diode

#37/42

Field effect transistor

Vdrain

VGS

Idrain

MOSFET (metal-oxide semiconductorFET), N-

type i.e. channel is n-type semiconductor, aka.

NMOS

Voltage between gate and source controls the

conductivity of the channel.

2. source

1. drain

3. gate

channel

No drain current flows via NMOS for VGS less

than certain positive value known as threshold

voltage Vth.

Practically no current flows ”into” gate IB≈0 A.

VGS

Idrain

Vthreshold

ideal switch

n-channel

FET

#38/42

Field effect transistor (2)

Vdrain

VGS

Idrain

MOSFET (metal-oxide

semiconductorFET), N-type i.e. channel

is n-type semiconductor, aka. NMOS

2. source

1. drain

3. gate

channel

Linear region

(’Ohmic region’)

0 V, ’cut-off’

In p-channel FET, PMOS, the direction of drain

current is reversed and the polarity of VGS is

opposite.

Combinination NMOS and PMOS can be used

for implementinc complementary MOS (CMOS)

logic gates.

#39/42

Example usages of

transistor

1. As a switch

FET closes the electrical circuit and let’s the current flow

Practically zero current goes from PIC to FET

Specific power-FETs can handle large currents

2. As inverting AC amplifier

This BJT has DC current gain hFE = β = 100

IB = (Vcc- 0.7V)/RB = 10.2 uA

IC = β * IB = 1.02 mA

quiescent Vo = Vcc – IC * RC = 5.2V

Vin > 0, increases IB and Vout will drop

With few additional R, the gain can be controlled regardless of β

g

d

sVGS

I

Device that takes

larger current than

available from PIC

Vdd

PIC

GPIO

IB

IC

0.7V

Vin

Vcc = 10V

Rb= 910 kΩ

b

c

e Vout

Rc= 4.7 kΩ

0V

C

#40/42

Integrated circuits

An integrated circuit (IC) combines many

components into single chip

Example ICs

microprocessor

memory

Ethernet controller

operational amplifier

74xx series, e.g. 8 * 2AND gates

Require larger package with more pins than

previously introduced components

Using ICs reduces the number of components on the

circuit board and increase their performance

#41/42

Operational amplifier

High-gain voltage amplifier

Very popular active component

Needs power supply and ground

Amplifies the difference between the two

input terminalsAn op-amp in a DIP

package

+

-

Vs+

Vs-

V+

V-.

Vout.

For any input voltages the ideal op-amp has infinite open-loop gain (i.e.

without feedback)

infinite bandwidth and slew rate

infinite input impedances (resulting in zero input currents),

zero offset voltage,output impedance, and noise

Circuit symbol of an op. amp.

#42/42

Operational amplifier (2)

Usually utilizes negative feedback (Fraction of) Vout is connected to input V-

Input signal is fed to input V+

Consequently, op.amp drives the output so that there is no voltage difference between V- and V+

Does not load Vinput (practically no current) but high current available at output

+

-R1

R2

VinputVout

Vout * R2/(R1+R2) = Vinput

Note! 0 V

Vout = Vinput * (R1+R2)/R2negative

feedback

I ≈ 0 A

Amplification is controlled with external resistors R1 and R2!