Family Name: _________________
First Name: __________________
48520
Electronics and
Circuits
Lab Notes
2013
PMcL
vS
500 mVpp
1.0 kHz
v2
1 k
-15 V
R1
v1
R2
10 k
10 F
6
4
TL071
2
3
+15 V
10 F
7
10 nF
10 nF
R
V
o
V
i
L
RL
Prepare for your exams
Study with the several resources on Docsity
Earn points to download
Earn points by helping other students or get them with a premium plan
Guidelines and tips
Prepare for your exams
Study with the several resources on Docsity
Earn points to download
Earn points by helping other students or get them with a premium plan
Community
Ask the community
Ask the community for help and clear up your study doubts
University Rankings
Discover the best universities in your country according to Docsity users
Free resources
Our save-the-student-ebooks!
Download our free guides on studying techniques, anxiety management strategies, and thesis advice from Docsity tutors
electronic lab
Typology: High school final essays
2014/2015
1 / 210
This page cannot be seen from the preview
Don't miss anything!
Partial preview of the text
Download Labnotes and more High school final essays Computer Science in PDF only on Docsity!
Family Name: _________________
First Name: __________________
Electronics and
Circuits
Lab Notes
PMcL
v (^) S 500 mVpp 1.0 kHz
1 k v 2
-15 V
R 1
v 1
R 2 10 k
10 F
6
4
TL
2 3
+15 V
(^710) F
10 nF
10 nF
R
Vi Vo
L
R L
ii
Circuit Breadboarding
Once a circuit has been designed, it must be tested. To do this quickly and reliably, a good breadboarding system is needed. It should allow for the easy interconnection and removal of the analog ICs, discrete components, power supplies, and test equipment. It is absolutely critical that connections between the breadboard, the components, the power supplies and the test equipment be mechanically and electrically sound. Most beginners spend more time running down poor or wrong breadboarding connections than they spend actually evaluating the circuit they have built. In this section you will find breadboarding hints that will help you minimize problems and errors in building your circuit for testing.
Figure 1 – Breadboard with ICs and other components inserted
The universal breadboard illustrated in Figure 1 provides a popular and convenient technique for circuit prototyping. Typically they give two to four busses (rails) for power supplies and ground, running along the edges. The body provides an array of solderless connections properly spaced and sized for most analog and digital ICs, transistors, diodes, small capacitors, 1/4 W resistors, and 22 AWG solid hook-up wire. Using it, you can construct circuits quickly, compactly, and reliably. These breadboards are available in a variety of styles and qualities from most electronic component suppliers.
iii
The connection diagram of a typical breadboard is shown below:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64
A 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 BC
DE
FG
HI
J
AB
CD
E
FG
HI
J
TL071 IC - note that it bridges the gap
There is a break
in these conductors.
You may want to put jumpers across.
We usually put +V here
and 0 V (common) here
We usually put -V here
and 0 V (common) here
Figure 2 – Connection diagram of wire sockets (holes) on a breadboard
The breadboard consists of two regions – rows and columns:
There are two sets of 64 columns each of 5 interconnected holes (A-E and F-J), to plug in components and connection wires.
There are four sets of 2 rows each of 31 interconnected holes, called ‘rails’. The two rails on each side are for connecting the power supply(ies). Typically, the rails are for the positive supply +V, the negative supply -V and for 0 V (common).
The universal breadboard provides a good interface between the components of the circuit, but care must be taken when you connect it to power supplies and test equipment. The breadboard is usually mounted on some larger, sturdier base (an aluminium plate).
Just as a chain is only as good as its weakest link, test equipment can perform no better than the technique used to connect it to the circuit under test. Excellent standard leads supplied with banana plugs, BNC connectors, or probes are common. Use them.
v
An example of a properly assembled breadboard is shown below:
Figure 3 – Neatly and correctly assembled circuit on breadboard
Observe the two sets of decoupling capacitors (one electrolytic, one ceramic in each set) connected as explained below:
One set of two capacitors connected between the +V rail and upper 0 V (common) rail.
The other set of two capacitors between the –V rail and lower 0 V (common) rail.
Of course, the upper and lower ground rails are interconnected with a wire strap.
Probes must also be used carefully. It is far too easy, when you are trying to touch a pin on an IC, for the probe to slip between two pins, shorting them together. This could damage the IC or supporting equipment. Instead of probing IC pins directly, you should connect a wire from the point you want to probe to a vacant part of the socket, where it can be secured and safely probed. Never probe IC pins directly.
vi
Layout Plan
a) Simplify the schematic and layout as much as possible for initial testing. Fine-tuning, zeroing, and additional stages can easily be added after you have the basic circuit working.
b) Be sure to include IC number, package type suffix, and pin numbers on each IC on the schematic diagram.
c) Make the layout look as much as possible like the schematic. Refer to the schematic whenever you debug your circuit.
d) Locate input and feedback resistors as physically close to the IC as possible. Long leads, connecting to remotely located resistors, pick up noise. This noise is then coupled to the highly sensitive input pin of the IC.
e) Keep the inputs well separated from the outputs to prevent oscillations.
viii
Circuit Testing
a) Analyse the circuit before applying power to ensure that you know what to expect.
b) Double check all connections, especially power supply connections, before applying power.
c) Apply power to the IC before applying the signals.
d) Measure voltages with respect to circuit “common”. If you need the difference in potential between two points, measure each with respect to earth and then subtract. The common terminal of some instruments (particularly the oscilloscope) may be tied to earth and would short out some part of your circuit. Or it may inject noise into a sensitive portion of your circuit.
e) When using the oscilloscope to measure voltages, be aware that the accuracy of an oscilloscope, as a voltmeter, is of the order of 3%.
f) To measure voltages accurately (better than 0.5% accuracy) use the Digital Multimeter. When measuring AC voltages with the Digital Multimeter, make sure that the frequency of the signal you are measuring is within the limits specified for your Digital Multimeter.
g) Measure current by determining the voltage across a known resistor. Then calculate the current. Ammeters are rarely sensitive enough, tend to load the circuit, and often inject noise into sensitive nodes.
h) Remove the signal from the IC before removing the power.
i) Change components and connections with the power off.
ix
Connecting Laboratory Power Supplies
Most regulated DC power supplies used in the laboratories usually contain two separate, adjustable DC power supplies, isolated from one another and ‘floating’ , i.e., not connected to earth. This is shown below:
15 V 1 A
15 V 1 A
black red black red
Figure 4 – Dual Independent Power Supplies
The BWD 604 Mini-Labs used in some laboratories do not have independent DC power supplies – they are connected in series and have one common terminal, as shown below:
15 V 1 A
15 V 1 A
blue white red
Figure 5 – Mini-Lab Dual Power Supply
xi
The photographs below show an example of such a Mini-Lab earthing connection according to the wiring diagram of Figure 7.
Blue Terminal: -V
Red Terminal: +V
White Terminal: 0
Green Terminal: Earth
Figure 8 – Mini-Lab Power Supply Earthing
Connection wires to the breadboard circuit:
Black: –V
Green: 0
Red: +V
Figure 9 – Details of “earthing” the common on the Mini-Lab Power Supply
Power supply connections to the breadboard and to the individual ICs can cause some other problems. For example, one sure way to damage an analog IC is to reverse the power supply connections. This can be easily prevented when you are breadboarding, by first labelling each bus in some highly visible way, for example, by colour coding. This should prevent you from connecting the IC to the wrong supply bus.
xii
Decoupling Capacitors
When analysing the AC small-signal operation of an electronic circuit, one assumes that the DC power supply of the circuit is a short-circuit for all the AC signals likely to occur in the circuit. In real-life situations, this assumption might be only wishful thinking, unless you make sure with appropriate measures that it really happens.
The laboratory power supply itself usually complies with this requirement, i.e. its output impedance is typically only a few milliohms over a wide range of frequencies.
On the other hand, the leads running from the power supply to the breadboard have some resistance and some inductance ; therefore, the power supply does not actually behave as a short circuit when seen from the breadboard. The stray impedance of the leads can cause stray coupling of signals from the output to the input of your circuit, producing unwanted feedback and unpredictable behaviour.
Also, high-frequency (often noise) signals can be picked-up by the leads. When coupled to or from one IC to another IC and amplified, these high frequency signals on the supply rails can cause the entire circuit to oscillate.
To avoid stray coupling via lead impedances, the connections to the power supply must be ‘ decoupled ’ or ‘ bypassed ’ with capacitors directly on the breadboard. The decoupling capacitors must provide, between the power supply connection points to the breadboard, a negligibly small impedance for all likely AC signal frequencies.
L1.
Lab 1 – Lab Equipment
DSO. Vertical setup. Horizontal setup. Trigger setup. Coupling of input signals. Automatic time measurements. Automatic voltage measurements. Cursor measurements. Reducing random noise on a signal. Dual power supply. Earthing the supply. Using triple supplies.
Introduction
The digital storage oscilloscope (DSO) is a versatile tool for the engineer. It has the ability to sample and store voltage waveforms, giving it the ability to “capture” transient waveforms and also the ability to perform mathematical operations on the sample values. Like any tool though, it has its limitations, and careful operation is required to interpret results correctly.
For professional design and testing, a constant DC voltage is usually required where the voltage can be adjusted from the front panel – such devices are DC power supplies. A power supply may have one pair of terminals, or two (a ‘dual’ power supply) or three pair (a ‘triple’ power supply). Some can be operated in series or parallel. You need to become familiar with the laboratory power supplies so that in future when you need to use one you know how they operate.
Objectives
- To become familiar with setting up a DSO.
- To become familiar with basic time and voltage measurement techniques using a DSO.
- To review the operation of a dual and triple power supply.
L1.
Basic Setup
You will be asked to perform various and wide-ranging tasks with the DSO during the laboratories, so it is important that you become familiar with its capabilities and limitations.
Function Generator Setup
- Turn the Mini-Lab on and set the function generator (FG) up for a sinusoidal wave of around 2 kHz. Set the amplitude to one quarter of the full range. Ensure the DC offset knob is set to ‘off’.
- Turn the DSO on and ensure the DSO has been set to its default setup configuration, by pressing the Save/Recall key on the front panel, then press the Default Setup softkey under the display.
- Observe the FG output using Channel 1 of the DSO.
Vertical Setup
- Push the 1 button. In the Channel 1 Menu, select the BW Limit softkey to “bandwidth limit” the channel, i.e. to attenuate high frequencies, which is generally “noise”. Bandwidth limiting Channel 1 will help create a “stable trigger”. Note the illuminated “BW” next to the Position knob..
- Turn the Volts/Div knob to 500 mV/div.
- Set the FG so that the sinusoid is 3 V peak-to-peak.
- Turn the Position knob and note the effect. Return the position to 0.0V.
- In the Channel 1 Menu, press the Coupling softkey until AC is selected. Note the illuminated “AC” next to the Position knob. Use the Coupling softkey to reselect DC.
- In the Channel 1 Menu, select the Invert softkey to “Invert” the channel. Note the status line shows that channel 1 is inverted (it has a bar over the 1). Turn the “Invert” off.
L1.
Horizontal Setup
- Turn the Time/Div knob and notice the change it makes to the status line.
- Press Main/Delayed. Change the Time Ref softkey to see the effect (note the trigger point / time reference triangle beneath the status line moves to show the position of the time reference). Return the Time Ref to “Center”.
- Use the softkeys to select different horizontal modes, and note the effect.
- Restore the horizontal mode to Main and display two cycles of the sinusoid.
- Turn the Delay knob to see the effect, and notice that its value is displayed in the status line. Reset the delay to 0.0s.
Trigger Setup
- Turn the trigger Level knob and notice the changes it makes to the display. Note that when the trigger level is set to a value that exceeds the bounds of our input signal, we lose the ability to trigger because the input signal never reaches the trigger level. Use the value in the status line to return the trigger level to 0.0V.
- Press Edge. Toggle each of the softkeys to see the effect and notice the change to the status line. Set the trigger to a positive edge on Channel 1.
- Press Mode/Coupling. Toggle between the Modes to see the effect on the status line. Set the Mode to Auto Lvl.
- Change the FG frequency to 3 kHz, then push the 10 Hz range button to obtain 3 Hz. Adjust the Time/Div knob to display two cycles of the sinusoid. Press Main/Delayed. Press the Roll softkey. Change the FG wave shape to triangle, then square, then back to sinusoid. Press the Single key. Press the Run-Stop key to trigger the DSO again.
- Set the DSO to Main Horizontal Mode and Auto Lvl Trigger Mode.