Design and creation of a circuit board

Transcription

1 Design and creation of a circuit board Lab Digital Technology March 19, EAGLE - Layout-Software For designing the schematic and the board-layout use the layout-software EAGLE (Einfach Anzuwendender Grascher Layout Editor). For your assignment use the EAGLE Light Edition which is available for free at: After the installation you're going to nd a manual and a tutorial in the doc-folder. Particularly if you have no experience with EAGLE, take yourself a little time for the tutorial especially chapter 12 to 14. From here on you're supposed to be familiar with the basic functions of EAGLE! 2 Designing the schematic according to the specication You will nd a special online tutorial by following this link: Do not simplify the equation you received in your assignment! Hint: Adjust the Grid in the layout-editor at 0,1 inch or 0,05 inch. The following components are used: 2 x Tip Switch (Library: switch-omron, name: 10-XX) 1 x 74HCT00 in DIL14 case(library: 74ttl-din, name: 7400N) 2 x LED green (Library: LED, name: LED5MM) 1 x LED red (Library: LED, name: LED5MM) 1

2 1 x Transistor BC237 (Library: transistor-neu-to92, name: BC237) or if you prefer SMD: BC848 SMD (Library: transistor, name: BC848) 2 x Resistor with 15 mm grid (Library: R-EU, name: R-EU_0207/15) 4 x SMD-Resistor (Library: R-EU, name: R-EU_R1206) 1 x SMD-Diode design Mini Melf (Library: diode, name: PMLL41SOD80C) 1 x Cable red 100 mm, cross section 0,5 mm2 1 x Cable black 100 mm, cross section 0,5 mm2 2.1 Drawing Frame Start by importing a drawing frame (Library: frames, name: A4L-LOC). Place the left bottom corner of the drawing frame at x = 0 and y = Power supply Supply voltage and ground are connected by two soldered on cables. Therefore use two wire-pads (Library wirepad, name: WIREPAD1,6/0,8). Now connect in the schematic the supply voltage with the supply-symbol VCC. the signal after the polarity diode with the supply-symbol +5V and ground with the symbol GND. You will nd all the symbols in the library supply1. The purpose of the symbols is to use multiple occurring signals in the schematic, like ground or supply voltage, without applying signal lines. This provides a better clarity. Please mark these lines, which need to be connected, with the junction symbol. 2.3 Creating and displaying input variables In order to create the input signals use two tip switches. Every tip switch is connected to +5 volt and A respectively B. After the tip switches the signals A and B each get pulled towards ground/gnd by a 10 kohm SMD-Resistor. This guarantees, that the input variables are always dened (ground respectively +5 volt). In order to display the input variables A and B use two green LEDs, and connect each by a resistor (grid = 15 mm) to ground/gnd. The current through the LEDs should be about 15 ma. Dimension the resistors. In order to display the output variable C use a red LED, which is switched by the transistor BC237. The base of the transistor is connected by a 10 kohm SMD- Resistor to a gate of the 74HCT00. Another SMD-Resistor before the red LED is adjusting the current. At dimensioning the resistor you should expect a supply 2

3 Figure 1: Quad 2-Input NAND Gate voltage of 5 volt, a collector-emitter-voltage at transistor Uce of 0,3 volt, and a voltage drop at the LEDs of 2,2 volt. The current through the LEDs should be about 15 ma. 2.4 Logic component 74HCT00 You're already familiar with the 74HCT00 from the laboratory tests. The component possesses 4 NAND-gates. Ground is located at pin 7, the supply voltage is supposes to be connected to pin 14. How to receive pin 7 and pin 14 for your gates you can look up in the Help-section of the EAGLE-command Invoke. It's up to you, in which order you're using the gates. Though, it's recommended to choose the corresponding gate-entrances and gate-exits in such a way, that their position on the board is as optimal as possible regarding the switches and the green output LED. A clever partitioning later simplies the routing of the signals. 2.5 Naming and labeling signals Well documented signal names are a big help when working with a schematic. Not only the comprehensibility of the schematic improves, but also a better allocation on the board is possible. Therefore you should give the logical names to all signals in the layout-editor. For example A, /A for not-a, /(A&B) for A-nand-B. Does one signal occur twice, number them all the way through. E.g.: /(A&B)_1, /(A&B)_2. Notice that EAGLE does not allow blanks for naming the signals. Make all naming visible by using the label-command, and arrange the names clearly. 2.6 Equation and truth table Document the boolean equation and the truth table inside the schematic (Text on Layer Info (# 97)). 3

4 3 Creating and routing the board 3.1 Dimension of the board Width (x): 55 mm Height (y): 45 mm Radius in the corners: 5 mm Use layer Dimension (# 20) with width = 0 for board-boundary. Hint: Adjust grid temporarily on 5 mm. While placing a component adjust grid on 0,1 / 0,05 or 0,025 inch. Rule: As roughly as possible as accurately as necessary. 3.2 Provide the board with four assembly-boreholes (Ø 3,2 mm) borehole 1 (x / y-position): 5 / 5 borehole 2 (x / y-position): 50 / 5 borehole 3 (x / y-position): 50 / 40 borehole 4 (x / y-position): 5 / 40 Provide each assembly-borehole with a round restrict-surface, Layer brestrict (# 42), diameter = 3,5 mm. Hint: Use the Eigenschaften-Menu (right mouse button) for placing the boreholes and surfaces accurately as well as for dening the diameters. 3.3 One-sided routing / maximum two bridges allowed Please route your board one-sided. Do not use the auto-router. There are maximum two bridges allowed. Therefore use the signals on the Top-Layer. You will have to replace these signals by wire bridges when assembling your board. 3.4 Signal range and clearance between signals The width of the lines should be at least 32 mil (ca. 0.8 mm), better 64 mil (ca. 1.6 mm). For lines leading through pins use 24 mil (ca. 0.6 mm). It's recommended to either congure this at the beginning (Menu -> Bearbeiten -> Netzklassen) or renish manually (Menu -> Change -> Width). In DRC (Design Rule Check, only in Layout/Board-View), use a minimum clearance of 8 mil (0,2mm) for those lines leading between pins as well as for smdpads. Otherwise you should use at least 12 mil (0,3mm) as a rule. 3.5 Fabricating the board Put your last-name on the bottom side of your board (Layer Bottom (# 16)). Use the text function for this. Type size is supposed to be 2 mm and important: font 4

5 = Vector. After you created and routed both the schematic and the board according to your assignment, you're supposed to send both EAGLE-les under your last-name (your_last_name.sch and your_last_name.brd) to the following -address: Afterwards, the board will be fabricated for you (milled & drilled), cleaned and coated with soldering varnish. The soldering varnish prevents oxidation of the copper tracks and eases the soldering. There are three dates for fabrication the board - please have a look at the deadline list. The EAGLE-les are accepted till 18 o'clock the day before the deadline. Schematics and layouts will be checked. Just such boards that meet all the requirements will be fabricated. The following checkpoints have to be checked before the les are sent: schematic provided with a frame all components present supply-symbols VCC, + 5V, and GND are used resistors are dimensioned properly polarity diode poled properly lines, that need to be connected, are marked with the junction symbol signals are labeled all component-symbols are clearly arranged both equation and truth table are on the schematic dimensions of the board are according the requirements vertex-radius of the board correct assembly-boreholes on the board (position, diameter) restrict-surfaces around borehole, Layer brestrict (# 42), D= 3,5 mm components clearly arranged width of circuit path (min. 32 mil, better 64mil, 24 mil between pins) observed all lines are routed last-name on bottom side, type size 2 mm, Font = Vector lename = last_name.brd, last_name.sch 5

6 3.6 Hand over of boards and components There are three dates (see event table) where boards, components and cable will be handed out by Mr. Meier or Mr. Scherr in room H Board soldering In the lab digital technology you will nd soldering-stations to solder your board. Additionally, several times a week there will be a tutor on-site to help you and answer your questions (see event table). The rest of the time you're free to use the lab as agreed by the person in charge. Digital Technology Lab H216 Some advices concerning your practical work: Soldering means to connect two metallic components by a liqueed metallic binder (solder). The trick is that the melting point of the solder is always lower than the one of the metal you're going to connect. Lies this melting point below 450 C we call it soft-soldering, otherwise we call it hard-soldering. At soft-soldering, the joints between the metal components, you're going to connect, are usually lled up with a tin alloy. It is important, that after cooling the tin alloy not just sticks on the surface of the other metal, but binds up with it. Therefore is has to liquidate and absorb a little of it, which means creating mixed crystals in the so called diusion-zone. This is up to the tin, while the remaining parts of the alloy are responsible for liquefying the solder and the mechanical stability of the connection. A soldered connection consists of ve layers: basic metal mixed crystal layer hardened solder mixed crystal layer basic metal. Most important for succeeding in creating a good soldered joint is absolute cleanliness. Conductor and components must be free of dirt, oil and oxidation. The soldering process itself consists of three phases: moistening, owing, binding. Thereby the working-temperature is an important criteria. The best temperature is the lowest one, on which all three phases can operate properly. For that some experience is required. A temperature-controlled soldering system facilitates the work. After cleaning the soldering bit, lead it to the soldered joint and heat it up. Afterwards lead the ux cored solder wire between bit and solder joint and melt it. Add more solder wire until the whole solder joint is moistened. Afterwards remove the soldering bit instantly in order not to overheat the liqueed solder. Let the solder cool o and avoid concussions. If the soldering bit is properly dimensioned, the whole soldering process should be completed after 2 to 5 seconds at most. According to experience, soldering electronic parts with lead-free solders will take longer. However, more than 5 seconds are not acceptable and indicate that the soldering iron is ether too cold or weak. INFO: Equip your board with an IC-socket (14-pole). It is soldered on your board instead of the 74HCT00. This preserves the 74HCT00 from being damaged by too much heat. 6

7 3.8 Solder the cables on As already mentioned, supply voltage and ground are connected by two cables. The cables should be about 100 mm long. The cable for the supply voltage has to be red, the one for ground black. You get cables the same way as components from Mr. Meier or Mr. Amann. In order to solder the cables on the wire-pads, you have to remove about 5 mm of the isolation, drill them, and tin them with solder afterwards you can solder them on. 3.9 Testing the board In order to test the circuit you should use a power source with at least 5 volt. But 6 volt would be better, because about 0,5 volt fall o at the polarity diode. At the soldering stations you will nd special boards with clips, which you can connect the circuit to in order to test it Presenting the board You can make an arrangement to present your board at any time to Mr. Meier in room H215. 7

8 4 Example: Schematic and board Figure 2: Schamatic example circuit Figure 3: Board example circuit 8