Fullscreen

the easy way into electronics This month we introduce a new way of working with electronic circuits – using Protoboards. They enable you to put a circuit together quickly without having to solder components into a PC board. You can make changes very quickly and when you’ve had your fun, you can pull it all apart and use the components for something else. A ctually, there is nothing new about protoboards. They have been used by engineers and technicians for making prototype circuits for around 20 years or more. In fact, that’s how most of the circuits published in SILICON CHIP begin life, as a “lash-up” on a protoboard. We have them in all sizes and have used them to “bread-board” circuits with as many as 40 ICs in some cases. So we thought it was high time that we described the concept to all our readers so that they (you) can enjoy their advantages. So what is a protoboard? As you can see from the photo, it is a plastic board with a multitude of holes in it into which you can plug ICs, transistors, diodes, resistors, capacitors and a lot of other components. The holes are internally connected in vertical (columns) and horizontal lines (rows). Protoboards are particularly useful for lashing up circuits with dual inline (DIL) ICs but are equally useful for circuits involving small signal transistors or a mixture of ICs and discrete components which is what most circuits tend to be. Fig.1 shows how the holes in a typical protoboard are connected together. The internal metallic connecting strips are shown in light blue. As you can see, there is a central horizontal channel and the ICs are plugged in to straddle this. Each pin will then be plugged into a column connecting strip, each connecting five By LEO SIMPSON SEPTEMBER 2000  69 holes together. So if you have an IC plugged in, you can have four components or leads connected to each pin. Then there are two rows of connecting strips at each side of the protoboard and these are broken in the centre by the “W” trademark. These eight strips are used for making positive and negative supply connections. As we will see later on, having the supply connectors broken in the centre makes it possible to have up to eight separate supply rails or decoupled supplies and so on. Don’t worry too much about the variations that are possible. Just remember that a protoboard of this style is broken up into a lot of vertical column connector strips for connecting to each pin of ICs and then there are long row strips which provide for power supply connections. The small 8-pin, 14-pin and 16-pin ICs are not the only ones that can be plugged in. You can also plug in any larger dual in-line IC whether it be a 40-pin job or larger, although since it will be wider, you will not be able to access all five holes on each column connecting strip. What size to buy? Protoboards, sometimes called “prototyping boards” or “electronic breadboards”, come in all shapes and sizes. What size is the best to buy? In our experience, you will probably want one which can accommodate up to about six to eight 16-pin ICs in a single line. Anything more than that and you are probably well acquainted with protoboards and already have one or more on your This rather tatty protoboard shows part of a circuit currently under development in the SILICON CHIP workshop. The beauty of protoboards is that you can make circuit changes quickly and easily, and without soldering. workbench. So to introduce this series of articles on protoboards, we have decided on a particular type which is readily available from parts retailers and which has the right combination of features. The one we have decided upon is the Wish WB-102 protoboard which is available from Dick Smith Electronics (Cat H-4044) at $18.63. Other retailers will have identical or similar breadboards available. For example, Jaycar have the WBU-202. It is a little smaller than the WB-102 model and it does not have the facility for splitting the supply lines but it will accommo- date the same number of ICs. Current and voltage ratings Before we go too far with proto-boards, we need to talk about the current and voltages that they can handle. In a word, “low”. They can’t handle high voltage (because there is a danger of flashovers” across the various connecting strips. And they can’t handle high current because the connecting strips are quite thin. Don’t even think about connecting up a protoboard circuit which runs directly from the 240VAC mains supply. This would be very dangerous as the closely-spaced connector strips would Fig.1: This diagram shows how the holes in a typical protoboard are connected together. The internal metallic connecting strips are shown in light blue. 70  Silicon Chip flash over between themselves or to the metal baseplate which we will come to later. Plus, the whole circuit would be a death-trap! Nor can you plug in components which have thick connecting pins or big solder lugs. This rules out most power transistors and Mos-fets, rectifier diodes, large electrolytic capacitors, wire-wound resistors and so on. The rule of thumb is that if you have to force a component lead in, it is too thick. However, you can still use all these components with protoboards, provided you solder thin connecting wires to each thick pin or lug. You’ll get the idea as we go along. By the way, if you are silly and do jam a thick component into a protoboard hole, you will find that, forever after, that connecting strip will then make poor contact with component leads. You should This is our sample protoboard mounted on a baseplate which has provision for pots, then mark those holes with a terminals and other hardware. The chaser circuit has been wired up with jump leads all the same colour – that might look neat but it is hard to follow. If you are buying a kit of Texta-colour pen to highlight jump leads, make sure they come in different colours. the problem strip. Back to voltage and current purchased the suggested protoboard or and so on. ratings: typically, you can use Another advantage of a metal baseprotoboards at voltages up to around one like it. Now what do you do with it? You can start plugging components plate is that it can be connected to one 50V (total) and at currents up to around 200mA without problems. Again, into it to make up circuits. However, to of the power supply lines or an Earth make it more useable, the protoboard line and effectively provide a “ground higher voltages will present problems of shorts and flashovers and higher needs to be mounted on a metal base- plane” for the circuit. This can be imcurrents will inevitably cause problems plate. Not only does the baseplate then portant with audio or RF circuits which provide a solid base for your circuits may otherwise be troubled with hum, with contact resistances and maybe but it can have provision for power instability or RF breakthrough. even local heating in the connector In fact, you can buy protoboards on strips. And we don’t want that, do we? supply connections, mounting holes for pots, switches and output terminals baseplates but they are quite a bit more OK, so let’s say you’ve gone out and expensive and they don’t provide for pots, switches etc. With this in mind, we have come up with a suggested baseplate design, as shown in the photos. This simply consists of a sheet Viewed from the front, showing how we’ve made provision for switches, pots and various other controls. The terminals, DC input socket and switch on the right aren’t “set in concrete”: you can move these around just as you can any other component on a protoboard. SEPTEMBER 2000  71 You can buy jump wire kits but you can make your own by just getting a length of 2-pair, 4-pair, 6-pair (or more) telephone cable and cutting lengths and stripping each end as you need them. Remember, you must use phone cable with solid core wires, not multi-strand. OK, that’s enough of the background; let’s put a circuit together. Chaser circuit Fig.2: we made our baseplate from a sheet of 18-gauge aluminium cut to 270 x 200mm. The section bent up at right angles to become the control panel has holes drilled for pots, input and output sockets, terminals and so on. There is also room for a battery pack, small loudspeaker, piezo transducer or other hardware which could be glued in place. of aluminium with a vertical section on one side. This has holes drilled in it to take the afore-mentioned pots, switches, terminals and so on. To make it, we obtained a sheet of 18-gauge aluminium measuring 300 x 300mm from Dick Smith Electronics (Cat H-2560). We cut it to 270 x 200mm, drilled a series of holes in it as shown in Fig.2 and then bent up a 70mm section at right angles to become the control panel. This baseplate is big enough to accommodate two of the Wish WB-102 protoboards side-by-side. The boards have matching lugs on their sides so 72  Silicon Chip that they can be locked together. Alternatively, there is room for a battery pack, small loudspeaker, piezo transducer or other hardware which could be glued in place. Wiring up circuits Plugging components into a proto-board is dead simple; in the case of an IC or transistor, you just line up the component leads with the holes you want and then push the component in gently. Then to make point-to-point connections on the board you need a variety of lengths of solid-core insulated wire, in a range of colours. For our very first sample circuit on a protoboard, we have chosen a simple chaser, as shown in Fig.3. This uses a 555 timer as an oscillator driving a 4017 decade counter. Five of the 4017 outputs are each used to drive a transistor and a LED. In fact, the circuit is identical to a chaser we published in the March 1994 issue. For those who did not see that issue, we will briefly describe the circuit operation. IC1, the 555 timer, is connected to oscillate at just a few Hertz by virtue of the resistors and capacitor connected to pins 2, 6 & 7. The square wave output from pin 3 of IC1 is fed to the clock input of IC2, the 4017 counter. IC2 is connected to continuously count up to five by dint of the connection of pin 1 to the reset input, pin 15. Each of the five outputs used will go high in turn and drive the base of an associated NPN transistor which turns on two LEDs in series with a 470Ω resistor. If you want a more complete circuit description you can refer to our article in the March 1994 issue which also featured a PC board. Now have a look at the photo of the assembled circuit and Fig.4 which shows the proposed wiring layout. Start by plugging in the two ICs, so that their notched ends face towards the lefthand end of the board. Then insert the resistors and capacitors. Note that the electrolytic capacitors must be correctly oriented otherwise they will have positive voltage applied to the wrong electrode and they won’t work. Next, insert the resistors and the LEDs. Note that the flats on the LEDs all face to the lefthand end of the protoboard. You can’t insert the trimpot as it is because its leads are too thick. You will need to solder some short tinned copper wires to each lead – use some pigtail lengths from a resistor. Finally, you can make all the component interconnections with the Fig.3: this chaser circuit uses a 555 timer as an oscillator driving a 4017 decade counter. Five of the 4017 outputs are each used to drive a transistor and a LED. solid-core jump leads. Don’t hurry the job because if you do, you will surely make mistakes. You will need to wire up a DC socket to suit a 6V DC plugpack to power the chaser. Alternatively, you could use a battery pack using 4 AA cells or better still, use a 6V lantern battery. A silicon diode between the supply socket and the supply line on the board protects components against accidental reversal of the power supply. This can be left permanently in place. Don’t forget to insert the two short jump leads which connect the supply lines along one side of the protoboard. Which ever way you do it, go carefully with the work and check it all carefully before applying power. When you do, you may find that some LEDs don’t light. Then it is a matter of checking your connections to the particular transistor and LEDs again and then making the correction. This is the beauty of protoboards. You can easily change the circuit – much easier than if you were assembling a PC board. OK, you’re probably itching to assemble a whole lot more circuits. Before you do, consider the circuit you have just built. Try playing around with it. Want less LEDs? Want more? Why Fig.4: you can use this wiring layout to connect up the chaser. Note that the trimpot will need thin wires soldered to its lugs before you can plug it in. SEPTEMBER 2000  73 And here’s what you see looking straight down on the protoboard. Compare this shot with Fig.4 on the previous page. As you can see, there is plenty of room on the aluminium baseplate for another protoboard (they interlock with the tabs you can see on the bottom and right), a small speaker, a battery pack or other bulky components or hardware. not try making it count to 6, 7 or 8 by connecting the reset (pin 15) to pins 1, 5 or 6 respectively (instead of pin 10). To add extra LEDs into the “chase”, simply duplicate the LED driver circuits (10kΩ resistor, BC547 transistor, 470Ω resistor and two LEDs). You might have to squash the layout a bit more but again, that’s the beauty of a breadboard. Want to make the LEDs run faster? Just reduce the value of the electrolytic capacitor connected to pin 2 of IC1. Want to make the LEDs run slower? Add another electrolytic capacitor in parallel with the one already connected to pin 2 of IC1. 74  Silicon Chip In other words, don’t be afraid to experiment as protoboards are ideal for this approach. Other observations Notice that we have used all the one colour for the jump leads on our protoboard chaser. While it looks neat, it is much harder to follow than if all the wire colours are different and that’s the way we have shown it on the wiring layout of Fig.4. You don’t have to be a genius to realise that this circuit could be wired up on the same protoboard in hundreds of different ways. No one way is necessarily better than another, although component layout can be very important in audio and RF circuits. We could also have eliminated quite a few of the jump wires by using the resistors themselves to make some of the point-to-point connections. We did it this way in an attempt to make it easier to follow. That’s all for now. We’ll present another protoboard circuit for you to SC experiment with next month. Acknowledgment: Our thanks to Dick Smith Electronics for supplying the protoboards and materials used in the preparation of this article.