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Chapter 6   1. We strongly suggest that all beginners buy a commercially available kit before embarking on any of these projects. The kit will contain all of the parts, the printed circuit (PC) board, solder and a B&W photocopy of the relevant article. This particular kit is for the Keypad Car Alarm, from the April 2003 issue of SILICON CHIP (note: this kit is now no longer available). 2. When you open the packet, you’ll find something like this inside: the components grouped into their categories (eg, all the resistors together), the PC board and the photocopy of the article. Don’t open the plastic and scatter the components everywhere: chances are that you’ll lose some. Always examine the PC board carefully, looking for any bridges that may have been formed between tracks and making sure that all the component holes have been drilled. In nearly all kits, you’ll have no problems in these areas. Building Project Kits You only need a few basic skills to successfully build electronic circuits. Here’s how to go about it. T HIS BOOK IS  structured around do-it-yourself electronic kits. Once built, all of the kits can achieve excellent results for far less cost than buying commercially available products – if in fact the commercial equivalents are available at all!. However, there is one important point to remember – to achieve a good outcome, you need to successfully build the kit. If you are experienced with electronic kit building, you can be forgiven for skipping this article. But that’s only if you know how to solder circuit components to a printed circuit (PC) board, with all the parts correctly located and installed the right way around to achieve an always-working project. If you’re inexperienced but still think that building a kit must be simple (after all, lots of people do it, 36 PERFORMANCE ELECTRONICS FOR CARS right?), stop right here! Think about this sobering fact: if you get even one component in the wrong place or soldered in the wrong way around, it’s unlikely that the kit will work – and it will never work unless the problem is tracked down and fixed. A kit that won’t work is not only very disappointing but irritating as well – and there are enough difficulties in modifying a car without trying to install a kit that doesn’t work. We’re not trying to put you off – even if you’ve never soldered before, with care and attention to detail, you’ll still be able to make the projects in this book. But it’s a bit like model-making – you’ll need steady fingers, you must check everything twice during assembly, and you must be able to follow diagrams very accurately. A variable output power supply allows you to easily test kits. A design like this one with variable current limiting will also instantly show you if you have a made a big mistake and have a short circuit or something equally catastrophic. If you’re on a tight budget, a car battery is fine as a source of power. siliconchip.com.au Parts List 1 PC board coded 03104031, 78 x 48mm 1 12-key numeric keypad (Jaycar SP0770 or similar) 1 8-way PC-mount screw terminal strip with 0.2-inch spacing 1 piezo transducer (Jaycar AB-3440 or similar) 1 14-pin DIL IC socket (cut for 2 x 7-way sockets) 1 18-pin DIP socket 1 7-way pin header 0.1-inch spacing 2 PC stakes 1 50mm length of 0.8mm tinned copper wire 2 1N914, 1N4148 diodes (D2,D3) 1 3mm red LED (LED1) 1 3mm green LED (LED2) Semiconductors 1 100µF 16V PC electrolytic 1 10µF 16V PC electrolytic 1 100nF MKT polyester 1 39pF ceramic 1 PIC16F84 programmed with Keypad.hex (IC1) 1 78L05 3-terminal regulator (REG1) 2 BC337 NPN transistors (Q1,Q2) 1 BD681 NPN Darlington transistor (Q3) 1 16V 1W zener diode (ZD1) 3 1N4004 diodes (D1,D4&D5)  Capacitors Resistors (0.25W 1%) 1 4.7kΩ 2 2.2kΩ 3 1kΩ 2 220Ω 1 10Ω 3. The part list is more than just a listing of the parts. Confused? Well, have a look at this one. Not only are the parts shown but for some of the components, the specific names that they are given on the PC board overlay are also nominated. For example, this parts list shows a BD681 NPN Darlington transistor. But in addition, it also has a “Q3” in brackets and on the overlay diagram, this transistor is shown as “Q3”. This numbering of the different transistors is important, as it indicates where they fit on the PC board. Similar numbering applies to diodes, voltage regulators and other components. 4. The parts overlay diagram is one of the most important parts of the instructions – it shows where each component goes. Not only that but when the component is “polarised” (ie, it must be soldered in the correct way around if it is to work), the overlay diagram shows the correct orientation. Look closely at the diagram at right – the orientation of each diode, integrated circuit (IC), transistor, LED and electrolytic capacitor is shown, indicated either by a band at one end (diodes), a dot at pin 1 (IC), the shape of the component (transistors and LEDs) or a “+” mark (electrolytic capacitors). Note that the resistors (all of them) and some capacitors don’t have a specific orientation – they are said to be non-polarised.   5. The first components to be placed on the PC board are always the resistors. These don’t have a polarity but they do have differing values, as indicated by colour bands. However, don’t worry about these bands; instead, use a multimeter to measure their resistance. Note that a 2.2 kilohm (2.2kΩ) resistor won’t necessarily have a value of exactly 2200 ohms – but it will be close. Use the multimeter to sort out each resistor’s value and then install it in the correct location. Some kits also have some plain wire links to be placed on the PC board – do these along with the resistors. siliconchip.com.au Parts Overlay Diagram  6. Next up are the diodes. These can come in different shapes and forms but they all have one thing in common – they are polarised and must be installed the correct way around. Use the parts list and overlay to sort out which diode is which and always orientate the board as it is shown in the overlay diagram. Install just one component at a time and check its orientation before turning the board over and doing the soldering. This gives closely-packed adjacent components a chance to cool and reduces the chances of making a mistake. PERFORMANCE ELECTRONICS FOR CARS 37   The transistors go in next. These have three legs and are polarised. The legs are often arranged in a triangular pattern, which makes getting the orientation right a bit easier. However, some transistors have their legs all in a line, so in this case, other clues need to be used. For this kit, the overlay clearly specifies which way the metal back of the transistor needs to face; this is also clear in the pics. Sorting out which transistor is which simply involves reading the type numbers printed on them and matching those up with the parts list. But take care – a voltage regulator often looks just like a transistor (three legs and so on) and must be orientated and positioned using the same basic approach. Next up are the capacitors. The polarised ones are cylinders marked with a line of negative (-) symbols next to one leg. Logically, the other leg is the positive – and that’s important, because it is the positive (+) side which is always marked on circuit and overlay diagrams. It’s really easy to get these around the wrong way, so take care. Other capacitors are non-polarised (ie, they can go in either way around) but they often have confusing markings (or codes). These are identified by the code descriptions given in the parts lists.   Last to be soldered into place will be any integrated circuits – called “ICs” or “chips”. In this case, a socket has been used – the IC then plugs into the socket. ICs must be orientated correctly to work and in this case you can see a cut-out at one end of the socket. This shows the end where pin 1 of the IC must be placed (represented by a dot on the IC’s body). Don’t orientate it just by the way the writing on the chip looks in the pics – this can change! If the kit uses a socket, make very sure that all the IC’s pins go into the socket – ie, that none are folded up under the body of the IC or pushed down the outside of the socket. Here is the nearly finished kit – the LEDs (their polarisation shown by a flat on the body), terminal block and ribbon cable (which goes to the keypad) have been added. Oh yes, and the IC has been plugged into its socket. No matter how strong the urge is, before you apply power, check each component against the overlay diagram. Is the orientation correct? Is it in the right place? Then turn the board over and check your soldering. Have you bridged any close tracks? Are any solder joints looking dull and suspicious or are they all shiny and bright, with the solder formed really well around the lead and track? Lots – and we mean lots – of people have torched their project through not making a last minute check of their work. Soldering Parts To The PC Board The first step is to turn the board upside down (ie, components on the bottom), so that the leads can be soldered. 38 PERFORMANCE ELECTRONICS FOR CARS Notice how the tip is applied to both of the bits to be soldered at once and not to the solder? Here’s what you’re aiming for: a bright, shiny fillet-shaped solder joint which has taken to both surfaces. siliconchip.com.au 11  If you intend to build only one or two kits, a general purpose soldering iron complete with stand and a reel of solder will suffice. The price is right (about $35 from Jaycar Electronics) and the iron will also be useful for making the soldered connections to car wiring. The alarm kit uses a remote keypad, connected to the board via 7-way ribbon cable. In the original instructions, ribbon cable isn’t used – instead the two parts plug into one another. But in this case, we wanted to mount the two parts separately, thus the use of the ribbon cable. In many cases, when building a kit, you may want to make minor changes like this – eg, when building the Smart Mixture Meter described in Chapter 8, you may want to use round LEDs (rather than rectangular) and mount them remotely from the board. WHAT’S POLARISED, WHAT’S NOT Many of the parts used in electronic kits are polarised – that is, they must be installed the right way around, otherwise they wont work and, in some cases, may even be damaged. Here’s what’s polarised and what’s not: ALWAYS POLARISED ICs, transistors, zener diodes, diodes, LEDS, regulators, voltage references, LCD and LED displays, batteries. MIGHT BE POLARISED Capacitors, piezo transducers, some switches (eg, BCD switches). NEVER POLARISED A few basic tools will make kit building a lot easier. Shown from left to right are: sidecutters, needle-nose pliers, a heatsink (that can be clipped onto components that would otherwise get too hot when being soldered), and a pair of pointy-nosed tweezers. All resistors, LDRs (light dependent resistors) most capacitors (but not all), wire links, fuses, trimpots and potentiometers (although these must usually be installed and wired the “right” way around to operate correctly), most switches, thermistors. Dry joint no. 1 . . . Dry joint no. 2 . . . A brittle joint . . . Oh no! The solder hasn’t taken to the PC board track at all – it’s just made a blob on the lead. This is a “dry” joint. Here’s another type of dry joint – some solder has taken to the PC board but only flux has stuck to the component lead. Not a “dry” joint but one destined to fail. It is brittle because something has moved as the solder hardens. siliconchip.com.au PERFORMANCE ELECTRONICS FOR CARS 39