Using solderless breadboards

Transcription

1 Page 1 of 9 Using solderless breadboards This document describes how to use the solderless breadboards available in the experimental didactic lab (LED, previously LADISPE) of Politecnico di Torino. 1 Setting up the circuit Each student team must come into the lab with the complete design of the circuit to be tested. That includes schematic diagrams, part list, and the planned sequence of measurements. Also a preliminary draft of the actual wiring (position of ICs, large components, supply lines, ) can be useful. After verifying the workbench setup, one person for each team must pick from the lab store all the devices required for the circuit. For some experiences a complete kit including all parts is provided in the lab; for other experiences the various parts must be taken from the lab component store at the beginning of the experiment. Warnings about parts available in the lab: - Parts placement can be wrong; verify the value of passive devices and the type of active devices (color codes, labels,.); - Faulty devices, or devices with wires too short or twisted (therefore not usable in the boards) should be returned to lab personnel (not placed again in the part store). - The wires (and device pins) inserted in the solderless boards must have 0,5-0,7 mm diameter (small resistors and capacitors); large wires or pins can damage the board contact springs. When the exercise is completed, parts taken from the lab component store must be placed back in the correct place. Faulty ones must be returned to lab personnel. Passive devices available in the lab store: carbon or metal film resistors ¼ W, 5 %, according to E12 sequence; various types of capacitors in the range 10 pf-1 F (ceramic, multilayer ceramic, plastic film), with tolerance 10 or 20 %, according to E6 sequence (with some value from E12); electrolytic capacitors from 1 to 200 F, tolerance 20 or 40 %; variable resistors and potentiometers of more common values (range 100 Ω 1 MΩ ) switches and LEDs (including a small PCB with 8 switch-led pairs), for logic states sensing and forcing; active devices as required by specific experiments. The design must use passive device as above. E6 (6 values/decade): 1, 1.5, 2.2, 3.3, 4.7, 6.8, E12 (12 values/decade): 1, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2 All the components here described are with lead, since they must be used on the lab solderless breadboards. Modern PCBs use extensively leadless SMD (Surface Mount Devices), not described here, and not available in the lab.

2 Page 2 of 9 Reading the value of passive devices The value of passive devices (resistor, capacitor) is expressed by printed numbers or colorcoded strips. First digit First digit Second digit Tolerance RESISTOR 473 Second digit Decimal multiplier Decimal multiplier CAPACITOR The color strips or the printed digits represent, from left to right in the drawing first digit second digit (third digit only for high precision devices, with 5 strips) multiplier (power of 10) tolerance (resistors and a few capacitors) Capacitors often carry also other information, such as voltage rating and dielectric type. Value of resistors is in ohm, for capacitors can be pf or nf Color Code: black 0 brown 1 red 2 orange 3 yellow 4 green 5 blue 6 violet 7 grey 8 white 9 For the tolerance strip: nothing 20% silver 10% gold 5% red 2% black 1% Other colors represent more tight tolerances (not used in the lab) Warning: Obtaining nonstandard values with parallel of series of two or more devices is not correct. Tolerances make the total uncertainty as wide as the difference between adjacent values of the E series used.

3 Page 3 of 9 Capacitors The various types of capacitors have different features and behavior. The proper capacitor type must be selected for each application; some hints are in the following. To provide information on size, each photo shows a ruler with marks at 1 mm intervals. Multilayer ceramic capacitors The value is specified by three digits, with meaning similar to color bands. These capacitors have small size and good performance at high frequency (if the leads are kept short!), but poor precision (20 % for higher values). They are the best choice for power supply bypass. With proper dielectric they can be used also for RF circuits. Plastic film capacitors They have good precision, but should be used only in low frequency circuits (up to a few MHz). Electrolytic capacitors The dielectric is a thin chemical layer, which is created by proper biasing; therefore these capacitors require applied voltage (DC+AC) to have a specific sign. High values with small size, but quite low precision ( %); used in power supply and audio frequency. Examples of tantalum capacitors (good also at high frequency) Examples of aluminum electrolytic capacitors Remember also that any capacitor has a maximum working voltage. The voltage values used in lab experiments are well tolerated by ceramic and plastic film devices, but must be verified for electrolytic capacitors. Warning: Electrolytic capacitors have specific polarity (the DC bias builds the insulation layer); with inverted polarization the device heats quickly and may explode.

4 Page 4 of 9 2 Setup of the solderless wiring breadboards Two different types of boards can be used in the lab: a. boards with banana connectors only b. boards with banana and BNC connectors Board a) Solderless boards Type a) boards have only banana connectors (no BNC). Coaxial cables must use alligator clops to connect to single wires pluggable in the contact matrix. Type b) boards include: Single-wire connections (banana plug) Single-wire connections (banana), to be used for power supply or other DC. Coaxial connectors (BNC), to be used for AC signals. BNCs are connected to the wiring posts; Black is the Ground, and Red the signal. Some boards have three BNC connectors and a different connection scheme to wiring posts. Verify the actual wiring on the bottom side of the board. Board b) Single-wire connections (banana plug) BNC Coaxial connectors (2 or 3) Solderless boards Wiring posts connected to BNCs 3 Solderless boards internal connections. Interconnections inside the board use cantiliver springs contacts inside each hole of the breadboard (shown by horizontal or vertical dashed lines in the drawing). Any wire plugged in the hole is automatically connected with the other ones inserted in holes connected by the dashed lines in the drawing. To avoid fake contacts and other malfunctioning, always check the wire segment plugged into the board: it must be straigth, clean, and of proper length (5 to 10 mm). Do not use oxidized, twisted, or too large wires; use a new piece of wire. Avoid also too thin wires, and be carefull to avoid insertion of insulated segments (remove at least 10mm of insulator at each end of wires).

5 Page 5 of 9 4 Map of internal boad connections Preferred position for supply voltages Some boards have conduction break here in orizontal bars (check the boards you are using!) + 12/15 V + 5 V Conduction break in vertical bars GND -12/15 V The drawing shows the connections among wire inserting holes. These connection can be grouped as: Four horizontal bus bars (in some boards with a break at the center check the boards you are using!), suitable for power and ground; Two groups of vertical bars, suitable for mounting various types of devices. 5 Dual-in-line packages Most active devices (ICs) available in the lab use Dual-In-Line (DIL or DIP) package, with pin numbering as in the drawing. Reference tab pin N Dot or mark Package (plastic) N-1 pin Pin 1 is marked by a dot or a tab on the package Looking at the device from top, numbering runs counterclockwise. In metal case transistors (TO5 and TO18) the package tab indicates Emitter. For any other information, refer to device data sheet.

6 Page 6 of 9 6 Circuit assembly Preferred position for supply voltages Conduction break in orizontal bars + 12/15 V + 5 V GND - 12/15 V Plan the circuit assembly, and place parts to reflect, to a reasonable extent, the positions in the electric diagram. To ease assembly and verification, all IC must be placed in the same direction (e.g. with pin 1 towards bottom left). For Op. Amp. use single-amplifier 8-pin ICs (more easily to assembly than dual and quad devices). For complex circuits build and test separate stages or parts, and then connect each other. For high-frequency and/or high speed circuits, place bypass capacitors between supply and ground. Use nf ceramic multilayer capacitors, placed as close as possible to Vcc/GND pins. 7 Connections Preferred position for supply voltages Some boards require jumpers to bring +5 V and GND to the right side bus bars. + 12/15 V + 5 V GND - 12/15 V Use the wires provided with the board and short jumper for GND and supply connections. As far as possible, connections should be direct and short. To power circuits in both right and left parts, some boards require jumpers at the center of on the horizontal bars (red circle in the drawing).

7 Page 7 of 9 The images in this page show examples of acceptable wiring (with custom-cut wires). If the special wires for breadboard are used, it is better to use short naked wires for power and GND connections. The first image represents a good wiring. The same circuit in the second image is still acceptable (wires are slightly longer, components are not shortened). When fixed length wires prepared with pluggable pins are used, consider that long wires may cause problems with medium and high-frequency signals. In any case, even in these boards is better to use short jumpers for GND and power suppli commections.

8 Page 8 of 9 8 What you should avoid Supply voltages in wrong position Missing 5V connection to the right side - 12 V + 5 V GND + 12/15 V Multiple chain connection Long wires Devices mounted across the same bus bar (short circuited). Use the horizontal connections only for power supply or ground (no signal); keep the polarity assignment proposed in the drawings. Do not use multiple jumps (chain connection), and keep wires short. This applies especially for high frequency connections, for wires carrying low-level signals, for high impedance nets (e.g. Op Amp input pins), ground and power supply. The following illustration is a collection of what not to do: long and crossed wires, chain connections on ground and power, The very high impedance of CMOS inputs brings open (input) pins to an unpredictable voltage level, depending from external electric fields. Besides wrong operation, this may cause damage to ICs (digital inputs are forced in the linear region, with high power dissipation). Therefore, never leave CMOS input pins open.

9 Page 9 of 9 Document history First DDC (pwp3) rev DDC (pwp4 - elesbm7a) rev DDC portato in WRD rev DDC documento autonomo (usobasx.doc) rev DDC inserite foto rev DDC English version rev DDC Content and language revision rev DDC Revised edition