Laboratory Practices for Electronic Prototyping: Equipment and Setup, Lab Reports of Electrical and Electronics Engineering

Download Laboratory Practices for Electronic Prototyping: Equipment and Setup and more Lab Reports Electrical and Electronics Engineering in PDF only on Docsity! COCO LABORATORY PRACTICES Step 1: Obtaining the equipment One team member should go to the north rear door of the studio and check out an electronic prototyping board, a protoboard. Remember that the protoboard number is a function of your computer workstation number, CS-n and to your section number, N: [18*(N-1) + n]. Write down the names of the team-members on this board. You will use this protoboard for the duration of this course. It should be returned in the same condition you received it in. Another team member should go to the south rear door of the studio and check out a toolbox. You need to deposit your Rensselaer ID card for this with the TA. The toolboxes will be shared among students in other sections as well as students in other courses, and should be handled very carefully. The instructor will usually bring the boxes with the parts you need to the instructor's desk. You must return the chips to the proper boxes after use. The chips are stored in the cabinet on the north end of the studio in labeled boxes. A list of all available devices is available from the course web page. Step 2: Getting to know the equipment A. The toolbox The toolbox consists of the following items: Multi-meter Use this to measure voltages, resistances, currents, etc. Logic probe Use this to probe the logic levels (0 volts and 5 volts). Connect the red wire to +5volts, and the black wire to ground (0 volts). Touch the tip of the probe to a part of your circuit to determine its logic level. The small lights on the probe indicate the logic levels. Wire stripper Use this to strip the plastic insulation off wires. Make sure that the stripped plastic is properly disposed of in the trash can. Wire cutter Use this to cut wires. Make sure that the small wire pieces are properly disposed of in the trash can. Long nose pliers Use this for bending wires. Chip puller Use this carefully to pull chips off the protoboard. Screw driver Use this to adjust device such as trimmed potentiometers. Power leads Use these to connect the power supply to the universal protoboards. Use the following color convention: Red: +5 volts; Green/Black: Ground (0 volts); Purple: -12 volts; Yellow: +12 volts. Computer Components and Operations Page 1 B. The prototyping board You will do all your wiring on Universal Protoboards (prototyping boards). These boards (see Figure 1) were custom fabricated at RPI for this course. The parts labeled 1 and 2 will be needed for the second half of this course and we’ll not worry about them now. You will build all your circuits in the areas labeled 3 and 4 . This area consists of an array of holes separated 0.1 inch from each other. The pins on integrated circuits (ICs), commonly referred to as “chips” are also separated 0.1 inch. The holes on the protoboard are connected internally in rows and columns as explained below. The areas labeled 3 in Figure 1 have two columns of holes each. These holes are connected together lengthwise, as indicated in Figure 2. These buses are usually used for power and ground connections. Do not place components such as integrated circuits (ICs) on this bus. 1 60 +5V+12VGND- 12V 1234 A B 1 2 3 4 5 6 7 8 9 A B C O M A B C O M UNIVERSAL PROTOBOARD Figure 1: The universal protoboard that you will use in the laboratory. The areas labeled 4 in Figure 1 have holes that are connected in the other direction. This part of the protoboard is where you will place ICs and discrete components such as resistors, capacitors, etc. Refer to Figures 2 and 3 for proper placement and connection of ICs. In these figures, there is a +5V "bus" and a GND "bus". Any wire connected to this bus will be connected to either +5V or GND (provided these power signals have been connected from Computer Components and Operations Page 2 circuit. Supply Bypass Capacitors help us in this regard. A capacitor has a high impedance to DC and a low impedance to voltage fluctuations. Putting a large (e.g.,. 0.1F) capacitor between the +5V and ground pins of your chips effectively short circuits the fluctuations without affecting the steady DC voltage. We can think of bypass capacitors as storing charge that can be used to quickly supply surge current needs. When wiring supply bypass capacitors, we need to be careful! Here’s why. When you pick a large (0.1F – 10F ) capacitor, you are most probably using an electrolytic capacitor. Electrolytic capacitors cannot handle both positive and negative voltages. They are usually marked quite clearly with plus + and/or minus – symbols to indicate their preferred polarity. You can damage them by wiring them with reverse polarity. Usually, the damage is accompanied with overheating, and sometimes a small explosion! C. The switches on the universal protoboard The upper left part of the universal protoboard consists of an array of switches and two push- buttons. They are described in detail below. It is suggested that you use the logic probe tool in your toolbox to get to know the operation of these devices. Switches 1,2,3 and 4: These are toggle switches that behave as follows. A B C O M A B COM When the switch is in the A position, the COM line is connected to A. When the switch is in the B position, the COM line is connected to B. These switches can be made to stay in either position for as long as we wish. Switches 5,6, and 7 (momentary toggle switches): These switches are similar to the first four switches except for the fact that they are spring loaded. They ordinarily stay in the A position, as shown below. A B COM Normal Position When operated, they do two things, as illustrated below:  disconnect COM from A for as long as the switch is pressed;  connect COM to B for as long as the switch is pressed. Computer Components and Operations Page 5 A B COM When Pressed Here are two ways to wire them up for use. The right-hand circuit is preferred. A B OUTPUT +5V = +5V in position A 0V in position B 1K A B OUTPUT +5V (not connected) = +5V in position A 0V in position B 1K Switches 8, 9: These are push-button switches, and have only two connections A and B, as indicated below. A B A B Button not pressed means no connection between A and B. A B Button pressed means A and B are connected as long as the button is held pressed. How you wire up a push-button switch makes a difference. You can wire up a push-button as either a high asserting or low asserting switch as shown below. Computer Components and Operations Page 6 +5V Low-asserting output (0V when pressed) 1K +5V High-asserting output (+5V when pressed) 1K D. Connecting power to the prototyping board Never apply power to your circuit until you have checked all connections carefully. In particular, check for short-circuits. Shorts between power and ground will probably not harm the power supply, but it could be disastrous to your circuit. Also check the polarity of devices such as electrolytic capacitors. Many devices can be destroyed by improper connection. The upper right portion of the protoboard consists of terminals for attaching the power cable. (It should be in your toolbox.) Use the following color convention:  Red: +5 volts  Green/Black: Ground (0 volts)  Purple: -12 volts  Yellow: +12 volts Step 3: Signoff and Cleanup Demonstrate your circuit to your TA and get it signed off. Cleanup after yourself. Specifically, make sure that there are no pieces of wires or plastic on the tables and floors. All pieces of wires are to be placed in the trash can or recycle box. Keep in mind that your TAs are instructed to not sign off on your activity unless you clean up properly. Computer Components and Operations Page 7