Diagnostic/Amplifiers

Temp. & Air Velocity Meter  Omega HHF51                            Photo

Microphone Preamp/P.S.   Larson Davis 2200C                  Photo

Strobe Light  1538-A  General Radio                                       Photo

Sound Level Meter  Radio Shack                                             Photo

Strain Gage Amp Rack   Vishay 2110                                      Photo

LVDT  Transducer   Amplifier   Schaevitz                                 Photo

Motors

Stepper                           2.3V  3A  100:1 reduction   with holding brake - photo

Stepper                           3.36V  2.9A  200 steps/revolution  100:1 reduction planetary - photo

Worm Drive DC             24V can be driven with different voltages for different speeds - photo

Stepper                           2.3A  1.8 degree/step - photo

12VDC  Pittman             187:1 planetary   With encoder - photo

Power Supplies

Agilent E3620A                       0-25V, 0-1A Dual Output - photo

HP E3631A                              0-6V,5A  +/- 25 1A - photo

Electro D-612T                        0-16V   10A - photo

HP 6653A                                 0-35V    0-15A - photo

HQPower PS23003AU           0-30V   0-3A Dual supply - photo

Pressure gages

Sensotec Model CP301                           0-4 bar ABS - photo.

Sensotec Model mg/7574-01                 5000 PSIG - photo

Sensotec Model A 5/7202-01-01            0-100 PSIG - photo

RDP LME30g1000K                                  0-10 BAR Gauge - photo

Sensotec Model 7351-02                         0-5 BAR ABS - photo

Sensotec Model Z/6902-03                      +/- 10 PSID - photo

DCT JKW5KGZ                                           0-1384 X100  inches H2O - photo

Sensotec Model 7776-01                         50 PSIA - photo

Sensotec Model 440/A556-02                  10-PSIA - photo

Capacitors

            Capacitors are energy-storage devices.  A capacitor of C farads with V volts across its terminals has a charge Q stored on one plate and –Q stored on the other plate.  Energy is stored in the electric field between the plates.  Capacitors are used for waveform generation and in integrators and differentiators (in integral and differential control, for example, which you may remember from your classes).  They are essential in filtering applications.  Electrolytic capacitors are used as power supply filters. When combined with a resistor, capacitors form low-pass and high-pass filters. 

Capacitor Varieties

Capacitors come in many varieties.  The above picture shows some of the capacitors that can be found around the electronics lab.

(a)   Electrolytic capacitors: These capacitors are available in W294 in ranges from 1-1000 mF.  These capacitors are commonly used in power-supply filters to smooth out fluctuations.  The most important thing to note about electrolytic capacitors is that they are polarized, i.e. the pin marked negative must be connected to a lower potential than the pin marked positive (see special note below).

(b)   Ceramic disc capacitors: These capacitors are available in values from 10 pF-220 nF in W294.  Larger values are available in W298.  Ceramic capacitors are common and inexpensive.  They are not polarized.

(c)    Various other capacitors: Other capacitors available in W298 include polystyrene, tantalum and metal foil.  See a staff member if you need a capacitor not available in W294.

(d)   High voltage capacitor: Very large capacitors are used in high-voltage and high-current applications to store and discharge large amounts of voltage.  The wire wrapped around the leads insures that the capacitor will not collect charge from its surroundings while in storage.  It is good to know that they exist, but you would not use high voltage capacitors except under supervision.

 

A special note on electrolytic capacitors: As mentioned above, electrolytic capacitors are polarized.  They will always be marked with a stripe on one side (see the photo below).  The stripe indicates the pin which must be kept at a negative potential relative to the other one.  For example, call the pin near the stripe (a).  The other pin is (b).  If (b) is connected to a positive voltage, (a) should be connected to ground.  However, if your power supply is giving a voltage that is negative with respect to ground, then (a) should be connected to the negative voltage and (b) to ground.  That way, (a) is maintained negative to (b).

 

Filters (Low-pass and High-pass)

Low-pass Filters (LPF)

            By combining a resistor with a capacitor as shown, you can make a low-pass filter.  The output is approximately equal to the input at low frequencies (approximately < 2pRC), but goes to zero for higher frequencies.  The capacitor will only allow current to flow through to ground it if it sees a high frequency voltage at the input.  Therefore, the above arrangement will allow low frequencies to get to the output side (V_o) while preventing higher frequencies from getting through.  This is a low-pass filter because lower frequencies are allowed to pass while high frequencies are blocked.

High-pass Filters (HPF)

Again, the capacitor will only allow high frequencies to pass through it.  Therefore, only high frequencies (approximately > 2p RC) can get through and low frequencies cannot.  This is why this circuit is called a high pass filter.

Operational amplifiers (op amps)

Much of modern electronics involves the use of Operational Amplifiers or Op Amps.  So, what are Op Amps?

·        The name Op Amp was originally given to an amplifier that could be easily modified by external circuitry to perform mathematical operations such as +, scaling, , etc. in analog computer applications.·        Now, they are basic building blocks in amplification, signal conditioning, filters, function generators, and switching circuits.·        An Op Amp amplifies the difference V_d = V₁ – V₂ between two inputs:

• A_OL = V_o/V_d is called the Open Loop Gain.  Typically, A_OL [10⁴, 10⁷].
• V₁ is called the inverting input and is labeled with a negative sign.
• The input signal V₁ is magnified and phase inverted at output.
• V₂ is called the non-inverting input and is labeled with a positive sign.  The contribution of V₂ to the output is phase-preserved.
• The maximum output voltage from an Op Amp is called the saturation voltage.  This voltage is approximately 2 Volts smaller than the supply voltage.  The Op Amp is typically linear over the range –(V_s - 2) < V_o < (V_s – 2).

Characteristics of Ideal Op Amps

• A_OL = - ¥
• Input impedance R_d between terminals 1 and 2 is ¥ Þ input current = 0.
• Output impedance is 0 Þ V_o is independent of load.

 

Your Friend, the LM324

            There are many different integrated circuits containing op amps, but the one you will use most often is the LM324.  This chip is a low power quad op amp, which means that there are actually four op amps contained in one chip.  LM324s are available for you to use in W294.  The spec sheet for this circuit can be found on the data sheets page of this website.

 

 

 

For descriptions of some useful circuits involving op amps, see the links below. 

Resistors

 

Resistors are one of the most common components you will run across. They are designed to dissipate electrical power in the form of heat (i.e. Ohmic heating) according to

 

Resistors are used as loads for active devices, in power circuits to reduce voltage by dissipating power, as a means of measuring and establishing current, to provide accurate voltage ratios, to set gain values, and many other applications besides.

Resistor Varieties

Some of the many types of resistors you may encounter are pictured above:

(a)   ¼ watt resistors, 5% precision: These resistors are available in many different resistances in the student electronics lab.  They are the most common type of resistor that you will encounter and work well for many applications.

(b)   1% precision resistors: These resistors are available in the ME Department electronics shop in W298 (ask one of the staff). 

(c)    Resistors for higher-wattage applications: Particularly in higher-current applications, you may encounter situations where a resistor will be required to dissipate more than ¼ watt.  If one of your ¼ watt resistors starts smoking, this is certainly true.  A variety of resistors are available in W298 that are rated for higher wattages.  Ask a staff member for assistance.

(d)   Potentiometers: These devices allow you to adjust resistances during operation of your circuit.  They are described in greater detail below.

Potentiometers

            Potentiometers (or pots) are very useful devices that allow you to vary resistance using a dial.  Note that the potentiometers shown above have three pins each.  The outer pins (1 and 2 in the figure below) are connected across a resistor whose value is marked on the outer case of the pot.  The middle pin is connected to a wiper that can be moved by turning the screw on top of the pot.  Depending on how they are connected, pots can be used in two different ways:

1. Pot used as a voltage divider: If all three pins of the potentiometer are connected, it can be used as a voltage divider.  A voltage divider is a very useful circuit element and is pictured below.  It can be used to set an input voltage to a certain level by adjusting the ratio between the two resistors R₁ and R₂.  When a pot is used as a voltage divider, pin 1 is connected to ground, pin 3 to power and pin 2 corresponds to V_A.  As the screw in the top of the pot is turned and the wiper is moved, the ratio R₁/R₂ is changed and the output voltage V_A changes accordingly. 
2. Pot used as a variable resistor: Suppose you simply connect pins 1 and 2 (or pins 2 and 3).  Then, as you turn the screw and move the wiper, the pot will act as a variable resistor.  Just be sure not to connect the two outside pins (1 and 3), because then the value of R will simply be equal to the value printed on the outer casing of the pot and will not change no matter how much you move the wiper.

How to read color codes on resistors

          Since you have a multimeter, the best way to determine the resistance of an unknown resistor is to connect it to a multimeter and read off the Ohms.  However, if you don’t have a multimeter handy, read the color code (i.e. striped color bands on the resistor) using the following rules:

• A gold band on the right side of the resistor indicates an accuracy of 5%.  That means that if the resistor has a resistance of 10 W, its resistance is 10 W ± 0.5 W.
• A silver band on the right side of the resistor indicates an accuracy of 10%.
• The last colored band shows the last digit, which represents how many zeros must be added to the numbers represented by the previous bands.Read left to right, the following values are associated with the corresponding colors:

Example:

Suppose a resistor has three stripes, green, blue, brown, read left to right.  What is the resistance? Green Þ 5; Blue Þ 6; Brown Þ 1;  The first two bands yield 56.  The last band, brown, represents how many zeros must be added to this number to obtain the resistance.  Since Brown has the value of 1, one zero must be added to the 56, so that the resistance of this resistor is 560 W.   

• Resistors also have another color code sometimes.  For example, the label “1213F” on a resistor signifies 121,000 W or 121 kW.
• When in doubt, connect the resistor to a multimeter and measure the resistance!

Strain Gages

Strain gages are devices which are used to measure deformation (i.e. strain) in an object.  The strain gage itself is made of metal foil connected to an insulating backing, which is attached to the object in question (this can be done with plain superglue).  Deformation in the strain gage causes its electrical resistance to change.  This resistance change can be measured using a Wheatstone bridge.

Transistors

A transistor is essentially an amplifier which uses a small input signal to drive a large amount of voltage or current (the additional power comes from the external power supply).  We will focus on one type of transistor for now, the NPN type.  There are several other types, most notably the PNP. Both NPN and PNP are considered BJT (bipolar junction transistors) devices.  They have opposite biasing polarities but very similar gain and current capabilities.

In considering the operation of an NPN transistor it may be helpful to think of the transistor as a valve where a voltage being applied to the base will cause a small current to flow between Base and Emitter. This is referred to as V_BE or in terms of current I_B. This small current will cause a larger proportional current to flow from Collector to Emitter, referred to as I_CE.  The ratio of I_B to I_CE is determined by the transistors gain. The gain of a transistor is expressed as b or more commonly as H_FE. This yields I_CE = H_FE I_B.

To correctly bias a NPN transistor you will need to remember several rules of thumb:

• The Emitter must be negative with respect to the Collector.
• The Base must be positive with respect to the Emitter.
• At least one diode drop is required to turn the transistor on.

Transistors come with a variety of different case styles.  Here are some of the varieties that can be found in W294 and W298.

(a)   Surface mount transistors: The pins connect to B and E.  C is the case itself.  This type of transistor will usually need to be mounted to a heat sink.

 (b), (c) and (d): Through hole transistors: Pins connect B, C and E.  The metal tabs in package (d) are for mounting a heat sink.

Before you wire a transistor into your circuit, you must check to see which pins connect to B, C and E.  You can do this by looking up the spec sheet of the specific transistor you are using.

Wheatstone bridges

Under construction.

How to use a multimeter

            Each station in the student electronics lab is equipped with a multimeter and two leads.  The multimeter is an instrument that allows you to measure resistances, DC voltages and DC currents, and root mean square (RMS) averages of AC voltages and currents.  Typically for a multimeter, Z_in ~ 10 MW, so it can handle a maximum frequency of 300 kHz and 1 mA at 100 W.   It cannot provide details such the time variation of a changing voltage or current.  This is best left to the Oscilloscope. 

            When the leads are placed in the above configuration, the multimeter acts as a voltmeter and can be used to measure DC voltages (using the “=V” button) and the RMS value of AC voltages (using the “~V” button).  It can also be used in this configuration to measure resistances (using the “2wire W” button).  If you want to measure the resistance of something, be sure that it is not part of a closed circuit or the measurement will not be accurate. 

 Using the Multimeter as an Ammeter

            You may have to change the configuration of the leads in order to use the multimeter as an ammeter to measure current.  Refer to the following table:

                                   

                                    Manufacturer                         Lead Requirement

                                    Keithley                                    No change

                                    HP                                           Change as shown

                                    Mastech                                   Change as shown         

Recall that a voltmeter works by placing a very large (ideally infinite) resistance in parallel with the component to be measured so as to find the voltage while drawing as little current as possible.  An ammeter works by placing a very low (ideally zero) resistance in series with the component to be measured.  When the leads are placed in the configuration below, it can be used to measure DC currents (using the “= A” option) and the RMS value of AC currents (using the “~ A” option).  Both of these options can be accessed by using the blue “Shift” button, which is marked on the photo below.

How to use an oscilloscope

            Each station includes an oscilloscope with two probes.  The oscilloscope is an instrument that basically displays the graph of an electrical signal, usually voltage as a function of time.  It is generally useful in cases where there is a rapidly changing voltage as a function of time.  Using the Oscope, you can determine:

• the magnitude of the voltage and how it is varying with time,
• the frequency of an oscillating signal,
• how much of your signal contains a DC component and an AC component,
• how much noise there is in your signal and how that noise is varying with time, and
• if there is a malfunctioning component in a circuit by observing the response of the circuit when it is subjected to a varying input.

Here is a typical digital oscilloscope: 

Typically, the front display will have three sections titled Vertical, Horizontal, and Trigger. 

Electronics can be analog or digital.  Analog equipment work with continuously varying voltages, whereas digital equipment use binary numbers that represent packets or samples of voltages.  An example of an analog equipment is the record player, while its counterpart the CD player is a digital device.  Oscilloscopes also come in analog and digital types. An analog oscilloscope works by directly applying the input voltage (i.e. signal to be measured) to an electron beam moving across the oscilloscope screen. The input voltage deflects the beam up and down proportionally, tracing the waveform on the screen.  In contrast, a digital oscilloscope samples the waveform and uses an analog-to-digital converter (or ADC) to convert the input voltage (i.e. signal to be measured) into digital information. It then uses this digital information to reconstruct the waveform on the screen.  Each has its own advantages.  Analog oscilloscopes are useful when it is important to display rapidly varying signals in "real time" (or as they occur).  Digital oscilloscopes allow you to capture and view events that may happen only once.  They can process the digital waveform data or send the data to a computer for processing. Also, they can store the digital waveform data for later viewing and printing.

The signal to be measured is fed to one of the input connectors, which is usually a co-axial connector called a BNC or N type cable.  If the input signal has its own co-axial connector, then a simple co-axial cable is used.  Otherwise, a specialized cable called a scope probe, supplied with the oscilloscope, is used. 

In its simplest mode, the oscilloscope repeatedly draws a horizontal line called the trace across the middle of the screen from left to right. One of the controls, the timebase control, sets the speed at which the line is drawn, and has units of seconds per division. If the input voltage departs from zero, the trace is deflected either upwards or downwards. Another control, the vertical control, sets the scale of the vertical deflection, and has units of volts per division. The resulting trace is a graph of voltage against time.  If the input signal is periodic, then a nearly stable trace can be obtained just by setting the timebase to match the frequency of the input signal. For example, if the input signal is a 50 Hz (i.e. 50 cycles per second) sine wave, then its period is 20 ms, so the timebase should be adjusted so that the time between successive horizontal sweeps is 20 ms. This operation is called a continual sweep. Unfortunately, an oscilloscope's timebase is not perfectly accurate, and the frequency of the input signal is not perfectly stable, so the trace will drift across the screen making measurements difficult. 

In order to provide a more stable trace, an oscilloscope has a function called the trigger. The trigger causes the scope to pause after reaching the right hand side of the screen, and wait for a specified event before returning to the left hand side of the screen and drawing the next trace.  Types of trigger or “specified events” include:

(1)   an external trigger or pulse from an external source connected to a dedicated input on the scope.

(2)   an edge trigger, which is an edge-detector that generates a pulse when the input signal crosses a specified threshold voltage in a specified direction.

(3)   a video trigger, which is a circuit that extracts synchronising pulses from video formats such as PAL and NTSC and triggers the timebase on every line, a specified line, every field, or every frame. This circuit is typically found in a waveform monitor device.

(4)   a delayed trigger, which waits a specified time after an edge trigger before starting the sweep. No trigger circuit acts instantaneously, so there is always a certain delay, but a trigger delay circuit extends this delay to a known and adjustable interval.

The effect of the trigger is to resynchronize the timebase to the input signal, preventing horizontal drift of the trace. Trigger circuits allow the display of nonperiodic signals such as single pulses, as well as periodic signals such as sine waves and square waves.

Most oscilloscopes have two or more input channels, allowing them to display more than one input signal on the screen.  Many oscilloscopes also allow you to bypass the timebase and feed an external signal into the horizontal amplifier. This is called X-Y mode, and is useful for viewing the phase relationship between two signals, which is commonly used in radio and television engineering. When the two input signals are sinusoids of varying frequency and phase, the resulting trace is called a Lissajous curve. 

Some oscilloscopes have cursors, which are lines that can be moved about the screen to measure the time interval between two points, or the difference between two voltages.  Usually the oscilloscope has a separate set of vertical controls for each channel, but only one triggering system and timebase.  A dual-timebase oscilloscope has two triggering systems so that two signals can be viewed on different time axes. This is also known as a magnification mode. The user traps the desired, complex signal using a suitable trigger setting. Then by turning on the "magnification", "zoom" or "dual timebase" feature, you can move a window to look at details of the complex signal.

Sometimes the event you want to see may only happen occasionally. To catch these sporadic events, some oscilloscopes have a "storage scope" feature that preserves the most recent sweep on the screen.  Some digital oscilloscopes can sweep at speeds as slow as once per hour, emulating a strip chart recorder.  Most fancy oscilloscopes switch from a sweep to a strip-chart mode right around one sweep every ten seconds. This is because otherwise, the scope looks broken: it is actually collecting data, but the dot or trace cannot be seen on the screen.

Oscilloscope Etiquette

• Never fiddle with another person’s scope.
• Always compensate an unknown scope’s probes.
• Never use 1x unless you are absolutely certain of the characteristics of the device being measured.
• Know your (electrical) ground.
• Avoid Autoscale!
• Always ensure that Z_in >> Z_out

Trigger

The trigger triggers the electron beam at a desired voltage level.  This level can either be set to the rising portion of the varying input voltage or the falling edge of the input.  This feature is very useful for single sweep, and can be delayed:

• Auto
• Normal
• Line
• External

DC or AC coupling

Vertical Amplification

• Sets the vertical deflection of the electron beam on the Oscope screen
• Allows you to measure peak-to-peak voltage
• Avoid full screen measurements
• AC or DC coupling

Horizontal Sweep

• Sets the beam speed across the Oscope screen in seconds
• Allows measurement of frequency, i.e. inverse of the period, of the input signal
• Allows you to measure towards the middle of the screen

Some useful stuff:1 ms = 1000 Hz = 1 kHz10 ms = 100 Hz100 ms = 10 Hz16.6 ms » 60 Hz

How to wire a breadboard

          Each station is supplied with a breadboard.  Breadboards are very useful for circuit design because they allow you to move components without having to constantly solder and de-solder connections.  The breadboards on the table are connected in the following way:

           

            The outer rails of the breadboard are typically connected to power and ground of whatever power supply you are using (or +V, -V and ground if needed).  The inner rows are used for the components of your circuit, and any ICs you are using go across the middle, as shown in the figure below.  Also, don’t forget to jumper the two halves of the outer rails.

 

How to wire your power supply

            Each station includes dual-output DC power supply, pictured below: The power supply can either be used as two separate 0-30 V supplies, or as one supply with a range of up to ±15 V.  The output current is 0-3 A.  The two switches above the green power switch (UI/UII and II/III) indicate whether the output from the left or right supply is being displayed on the built-in voltmeter and ammeter.  When plus and minus voltages as required, you must connect the positive terminal of one output with the negative of the other using the following scheme:             Jumper the positive output of the left supply with ground on the right.  The two middle terminals become your ground, marked with black arrows.  The leftmost terminal is your negative voltage out, marked by a white arrow.  The rightmost is positive voltage out and is marked by a red arrow.            Use of these power supplies can be confusing at first.  If you are unsure what to do, ask a staff member in W298.