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The most important tools
for product development are- CAD software, CNC router, and an
Oscilloscope. Here is our recommendation for a low cost Oscope with
lots of options-
|
Channel |
2 Channels |
|
Impedance |
1MΩ
25pF |
|
Coupling |
AC/DC/GND |
|
Vertical
resolution |
8Bit |
|
Gain
range |
10mV-5V,
9Steps |
|
DC
accuracy |
±3% |
|
Timebase
range |
4ns-1h,
38
Steps |
|
Vertical
adjustable |
Yes |
|
Input
protection |
Diode clamping |
|
X-Y |
Yes |
|
Autoset |
Yes (30Hz to 40MHz) |
|
EXT.
input |
Yes |
|
Trigger
Mode |
Auto,
|
|
Trigger
Slope |
+/- |
|
Trigger
level
adjustable |
Yes |
|
Trigger Type |
Rising
edge,
falling
edge |
|
Trigger
Source |
CH1, CH2, EXT |
|
Pre/Post
trigger |
0-100% |
|
Buffer
size |
10K-32KB/Channel |
|
Shot
bandwidth |
DC
to 40MHz |
|
Max.
Sample
rate |
100MS/s |
|
Sampling
selection |
Yes |
|
Waveform
Display |
port/line, waveform
average, persistence, intensity |
|
Network |
Open/Close |
|
Vertical
mode |
CH1,
CH2,
Dual,
ADD |
|
Cursor
measurement |
Yes |
|
Spectrum
analyzer |
|
|
Channel |
2 Channels |
|
Math |
FFT,
addition,
subtraction,
multiplication,
division. |
|
Bandwidth |
40MHz |
|
Cursor |
Frequency,
Voltage |
|
Data
Samples |
10K-32K/Channel |
|
Accessories |
S/W CD, probes, manual, USB cord |
DSO-2090 - 100MS/s, 40MHz
Bandwidth Digital
storage
oscilloscope
that
uses
the
USB
port
on
your
computer.
It
has
2
channel
input and external trigger option. 23 measurement functions plus
FFT. Great for documentation, lab work, experimentation, and education.
Characteristic
ONLY
$185 - Plus $20
shipping -
Or if you
prefer using Paypal, log on and send funds ($205.00) to
Outside
the US please email for shipping costs.
*Faster
Oscopes
are
also
available.
Electronics
reduced
to
it's
simplest
form
is-
the flow of electrons are either on or off, or they
vary between on and off. These two methods of controlling electricity
are known as digital
and analog electronics. A light switch turns a light on and off
(digital) and a light dimmer turns a light to any point from
off to on (analog). A computer is a digital device that contains may on
/ off switches.
The
flow
of
electricity
is
either
direct
current (DC) or alternating current (AC). A battery is an
example of DC, and the power in your house is AC. AC has
advantages in power distribution. DC has power losses in the long
transmission lines that AC can reduce. More on this later, first
lets talk about the common parts used to control electricity.
This
is
very
important
-
complicated
circuits
are made from many simple sub-circuits wired
together to perform complicated functions.
CircuitMaker
for
students
is
a
schematic
capture
and simulation program and is included free on the
Pilot Pro plans CD or you can find it on the web. The program is to
large to fit on my URL.
Common
formulas:
E=Volts (electromotive force), R=Ohms (resistance), I=amps (current),
P=Watts (power)
Common
components
used in
electronics:
Resistors (Ohms) - oppose current by producing a voltage drop, converts
Voltage to a current.
Capacitor (Farads) - stores electrons, blocks DC and passes AC
Coil (Henry)- passes DC and blocks AC
Transformer - changes voltage to a higher or lower value and changes
the current inversely
Transistor - turns electron flow off and on,
or varies the flow from off to on.
Diode - blocks the flow of electrons in one direction. The arrow points
in the positive direction. A- anode +, K- cathode -.
LED - light admitting diode
Always read the data sheets on components for more information.
Resistors
Values can be changed by add components in parallel or series.
The smaller resistor in the parallel circuit dominates the total value.
The larger resistor in the series circuit dominates the total value.
Resistor
used
as
a
current
sense.
A resistor limits current and drops Voltage and can be used as a
current to Voltage converter using Ohms law - I=V/R.
The color code value for resistors:
| color
|
Value |
For memorization | Tolerance |
| Black |
0 |
Bad |
|
| Brown | 1 |
Boys |
+- 1% |
| Red | 2 |
Rape |
+- 2% |
| Orange |
3 |
Our |
+- 0.05% |
| Yellow |
4 |
Young |
|
| Green |
5 |
Girls |
+- 0.5% |
| Blue |
6 |
But |
+- 0.25% |
| Violet |
7 |
Violet |
+- 0.1% |
| Gray |
8 |
Gives |
|
| White |
9 |
Willingly |
|
| Gold |
+- 5% |
||
| Silver |
+- 10% |
||
| None |
+- 20% |
Time
constants
Time constants: For resistor/capacitor -- Vt = E (1-e *
(-t/RC)). For resistor/inductor (time for current to reach full
value) -- It = E/R * (1-e * (t*R/L)). Where R is in ohms, C
is in farads, L is in henries, t is in seconds, and e is in the natural
log base 2.71828.
One time constant (R*C) is equal to 63.2% of the final value.
After the second
time constant an additional 63.2% of the remaining charge or current
will be reached (63%, 86%, 95%, 98%, 99%). The same is true for
discharge. Three to
five time constants are need to get close to full charge or current.
RC time constant
Capacitor values
cap marking = size in pF
105 = 1,000,000pF or 1000nF or 1uF
104 = 100,000pF or 100nF or 0.1uF
103 = 10,000pF or 10nF or 0.01uF
102 = 1,000pF or 1nF or 0.001uF
101 = 100pF or 0.1nF or 0.0001uF
pF = picoFarad, nF = nanoFarad, uF = microFarad
Driving
an
LED
LEDs or light admitting diodes drop about 2 Volts before they conduct.
Check the specification sheet for Vf (forward Voltage) and max current.
This LED is rated at 1.7 Volts before it will start to turn on and can
use 0.04 amps of current. We need to have a resistor that will limit
current to no more than 40 ma or the LED will burn out and fail. Ohms
law says R=E/I, we need to subtract
the LED Voltage drop from the calculation so R=(9-1.7)/0.04 = 182.5.
Round this up to a standard resistor value you get 200 Ohms. If the LED
specs are not known then try using Vf = 2V and LED I = 0.02 amps as
ball park ratings.
Changing
Voltage
levels
Wrong-
Right- Voltage divider
Vout = Vin*(R2/(R1+R2)) = 10*(10k/(10k+10k)) = 10*0.5 = 5V
The down sides are this supply is current limited and Vout changes as
Vin changes.
Voltage
reference
D1=5.1V Zener diode, R1 = (Vin min - Vz) / (Imax) = (10-5.1) /
(0.01) = 490 round up to 499 standard value.
Zener diodes have a reverse voltage breakdown point. This Zener Voltage
point depends on the diode part number.
Standard resistor values can be found in a Digikey or Mouser catalog.
Voltage
Regulator
D1=5.6V
Zener
diodes
are
designed
to
be
hooked
up
backwards
because
they
start
to
conduct
at
a specific reverse Voltage. The resistor limits current
through the diode and transistor base. The transistor drops about 0.4V
through the base - emitter
junction. The transistor is wired as a Voltage follower or common
collector. With the transistor added the output can supply more
current. This transistor can supply about 200ma of current.
Integrator
The integrator
is used
for a signal delay or low pass filter. If
the RC time constant is a 10th (1/10) the period of the signal then it
has a high amplitude. If the RC time constant is 10 time the period of
the signal then it acts like a first order filter.
The signal period is 1/1000Hz = 0.001, the RC time constant is
30000*0.0000000047 = 0.000141. The RC time constant is set at 1/10 that
of the signal period.
Here the
RC time constant (R = 100K, C = 1uF) is set at 10 times that of the
signal period. the RC
time constant is 100000*0.0000001 = 0.01. This looks like a low pass
filter.
Differentiator
The differentiator is used as a trigger or high pass filter. If
the RC time constant is a 10th (1/10) the period of the signal then it
has a high amplitude. If the RC time constant is 10 time the period of
the signal then it acts like a first order filter.
The
signal period is 1/1000Hz = 0.001, the RC time constant is
30000*0.0000000047 = 0.000141. The RC time constant is set at 1/10 that
of the signal period.
Here the RC time constant (R = 100K, C = 1uF) is set at 10 times that of the signal period. the RC time constant is 100000*0.0000001 = 0.01. This looks like a high pass filter.
The
integrator
and differentiator
circuits
above
are
made
from
a
RC
Voltage
divider
circuit.
The
capacitor
is
like
a
variable
resistor and it's value is base on the frequency
passing thought it. This is called capacitive reactance. The formula
for capacitive
reactance
is
Xc
=
1/(2*Pi*frequency(Hz)*Capacitance(F)).
Reactance for caps and
inductors
*Voltage and current phase rule of thumb:
Voltage leads current in an inductor by 90 degrees-
Current leads Voltage in a capacitor by 90 degrees-
Triangle
to
sine
converter
Diodes are one way valves. The diodes start to turn on at about 0.7V
(forward Voltage
drop). When the diodes conducts the resister drops some Voltage and
limits current.
Silicon diodes drop about 0.7V, germanium diodes drop about 0.2V. The
resistor also limits current through the diodes. To much current will
destroy the diodes.
Diode
Curve
trace
Here is the curve trace of a diode. This shows the Voltage /
current response of a forward biased diode. The current through the
diode is monitored as a DC sweep of the Voltage from 0.25V to 1.5V.
Curve tracer
OPEN
SHORT
RESISTOR
DIODE
ZENER
CAPACITOR
EMITTER
BASE
EMITTER
COLLECTOR
Sinusoidal Voltage and
current
Effective Voltage = 0.707 * Peak [Also know as Root Mean Square (RMS)]
- do this in the reverse order (square, mean, root) to get an RMS
number.
Half cycle average = 0.637 * Peak
Peak Voltage = 1.414 * effective
Effective Voltage = 1.11 * average
Transistor
configuration (bipolar)
letter
Meaning
For memorization
B|E|C -common
-Bob eats carols
P|V|I -gain
-Pretty veal in
A|B|G -alpha, beta,
gamma -a big garage
L|M|H -input impedance
-liking mostly her
H|M|L -output impedance
-hot moist loins
-----------------------------------------------------------------
NPN - negative, positive, negative - (Not Pointing iN)
PNP - positive, negative, positive
*
Bipolar transistors are current controlled devices. FET transistors or
Voltage controlled.
* A transistor is said to be in its active mode if it is operating
somewhere between fully on (saturated) and fully off (cutoff).
* Base current tends to regulate collector current. By regulate, it is
meant that no more collector current may exist than what is allowed by
the base current.
* The ratio between collector current and base current is called "Beta"
(β) or "hfe". hfe varies and is not a good parameter.
* β ratios are different for every transistor, and they tend to change
for different operating conditions.
* The Vbe (Voltage across the base and emitter diode junction) is about
0.6 to 0.8V.
*Vcc is collector Voltage, Vee is emitter Voltage refering to NPN type
Transistor calculations
The transistor above has a hfe of 100 and we want 20mA and 5V at
the collector.
hfe = Icollector / Ibase and Ib = Ic / hfe, Vbe = 0.7V
Ib = 20mA / 100 = 0.2mA
+12V - IbRb - 0.7V = 0 so Rb = (V - Vbe) / I or Rb = (12V - 0.7V) /
0.0002A = 56,500 Ohms
AND
+12V - IcRc - 5V = 0 so Rc = (V - Vce) / I or Rc = (12V - 5V)
/ 0.02A = 350 Ohms
Transistor
as
a
switch
The
Gnd out Vc is ~ (about) 0.05 to 0.2V at saturation.
Common emitter circuit for a 200ma load and hfe = 100.
Ibase = Icollector / hfe (0.002 = 0.200 / 100)
R2 = V1 - Base Emitter V drop / Ibase (5650 = 12 -
0.7 / 0.002) Round R2 down to the standard 5.6k, 5% value due to the
drop in gain or hfe.
This switch is an inverter. When the base is high the output is low or
sinks current.
As the the transistor goes into saturation (full on) the hfe rating
drops off (gain decreases).
Protect the collector from going lower than the base with a reverse
diode to ground at the collector, as in AC loads. Or a diode reversed
biased across an inductor load.
Emitter
follower
The emitter follower or Voltage
follower output follows the input minus the Vbe Voltage drop of about
0.7V. The advantage of this circuit is you can buffer the driver signal
from the load. This circuit has current gain and can source low
impedance loads.
ΔIe = ΔVb / R1
ΔIb = 1 / (hfe +1) * ΔIe = ΔVb / R(hfe + 1)
Rin = (hfe + 1) * R1 + R2
Transistor
as
an
amplifier
-More on the way-