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The Breadboard

Discussion in 'Electronic Theory' started by ElectroMaster, Jul 26, 2002.

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  1. ElectroMaster

    ElectroMaster Administrator

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    Introduction
    When building a permanent circuit the components can be grown together (as in an integrated circuit), soldered together (as on a printed circuit board), or held together by screws and clamps (as in house wiring). In the laboratory, we want something that is easy to assemble and easy to change. We also want something that can use the same components that real circuits use. Most of these components have pieces of wire or metal tabs sticking out of them to form their terminals.

    How it Works
    The heart of the solder-less breadboard is a small metal clip that looks like this:

    [​IMG]

    The clip is made of nickel silver material which is reasonably conductive, reasonably springy, and reasonably corrosion resistant. Because each of the pairs of fingers is independent we can insert the end of a wire between any pair without reducing the tension in any of the other fingers. Hence each pair can hold a wire with maximum tension.

    To make a breadboard, an array of these clips is embedded in a plastic block which holds them in place and insulates them from each other, like this:

    [​IMG]

    Depending on the size and arrangement of the clips, we get either a socket strip or a bus strip. The socket strip is used for connecting components together. It has two rows of short (5 contact) clips arranged one above another, like this:

    [​IMG]

    The bus strip is used to distribute power and ground voltages through the circuit. It has four long clips arranged lengthwise, like this:

    [​IMG]

    Note that in their infinite wisdom, the manufacturer elected not to join the adjacent contact strips into a single full-length contact strip. If this is what you want, you will have to bridge the central gap yourself.

    When we combine two socket strips, three bus strips, and three binding posts on a plastic base, we get the breadboard:

    [​IMG]

    In this picture we have replaced the plastic covers, hiding the connections

    The breadboard lets us connect components together and by wiring the bus strips to the binding posts and the binding posts to the power supply, to connect the power supply to the circuit. Now what we need is a way to bring connections from the rest of the instruments into the breadboard.

    Organizing Your Breadboard
    The first few Labs are something of a "warm up" in terms of utilizing the breadboard. We will use only one or two of the components at first and will build circuits consisting of more components near the end of lab sessions. As we get closer to the final lab, we will be constructing more complicated circuits having more external connections.

    To keep the boards from degenerating into chaos, we need to organize the layout and wiring on the breadboard.

    There are several aspects to this organization ranging from small details to the big picture.

    Colour Coding
    The wire reels contain an assortment of different coloured wires. You could just pick pieces of wire at random, or you could try to use the different colours to designate different signals. There aren’t enough colours for every signal, but you can use different colours to denote different classes of signals.

    One set of signals you should colour code are power and ground. In particular, you should have a different colour for +15 V, -15 V, and ground and you should not use any of these colours for other signals. It would be nice to use "standard" colours for these, but unfortunately there are several competing standards. One colour that nearly everyone agrees on is that red should be the positive power supply voltage. Most automotive and electronic wiring uses black to denote ground. Electronic wiring which uses black for ground often uses blue for the negative supply.

    An example of colour coding the wires on your breadboard:

    • red = +V (positive voltages)
    • green / black = GND/Common/0V
    • blue = -V (negative voltages)
    • connections = your choice

    Real World Problems
    On paper all our components are ideal and no components exist where we don't draw them. In an actual circuit, things are not quite so tidy, wires have non zero resistance and inductance, sources have output resistance, parasitic capacitances and mutual inductances exist between wires, and a host of other gremlins. In addition, although we are only applying input signals from Hz to MHz, the active devices (op amps and transistors) we use have gains at frequencies up to a few MHz or 100s of MHz. This means that all of the pieces of wire can become fairly effective aerials, radiating energy to (and receiving from) the rest of the world, and more significantly, to other parts of the circuit.

    What all this means is that a circuit which is wired correctly may fail to function as expected. Although we can't eliminate all of these effects, we can do some things to minimize them.

    Layout
    Try to arrange your layout so that each function is grouped together in a single area of the board and so that stages that are connected together are close to each other. This will allow connections to be made with shorter wires. Also try to avoid having high level signals near low level stages.

    A Twist on Wire
    One way to reduce unwanted coupling between different signals in your circuit is to use twisted pairs, i.e. a pair of wires twisted together. This can reduce the wire acting as a aerial picking up unwanted noise and signals, from within and external to your circuit.

    [​IMG]

    Routing
    Twisted pair or not, try to keep wires carrying high level signals (large voltages, currents or high frequencies) away from those carrying low level signals. Keep outputs away from inputs, especially in sub-circuit. It's better for wires to cross at right angles than to run parallel to each other.

    Bypass/Suppression Capacitors
    Another path for unwanted noise is via the power supply. To reduce this, use some of your capacitors can be used i.e. connect them between the power supply voltages and ground (be sure to observe correct polarity on the electrolytic capacitors). Ideally each op amp should be bypassed, but you may be able to get by with capacitors at each of the inputs for the entire circuit.

    Wiring Techniques
    The basic idea of wiring on a solder-less breadboard is simple: just stick the ends of the component leads or wires into the holes. But like any seemingly simple process, there are a few subtleties that can make the difference between success and failure.

    First a note of caution, the material that the clips inside the breadboard are made of is a compromise between good conductivity, corrosion resistance, and springiness.

    The elastic limit is considerably less than of a good steel spring and if spread too far, can be permanently distorted. To avoid deforming the connector clips, Never insert more than one wire in a hole.

    With the health of our breadboard assured, there are a few more things we can do to make sure that our connections are good ones.

    Strip about 5 mm of insulation from each end of a piece of wire. Less than that raises the risk that insulation will be forced between the fingers of the clip. More leaves bare wire exposed that can short to adjacent components. One exception: strip about 15 mm from the end of a wire that will be clamped in the binding posts.

    When inserting a small wire or component, use your needle nosed pliers rather than your fingers to hold it.

    If the end of a wire becomes kinked, cut it off or use your pliers to straighten it.

    [​IMG]
     
  2. chesart1

    chesart1 New Member

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    If you have two inductors in the same circuit and you do not want any magnetic coupling between the two inductors, how would you arrange the two inductors on the board?

    Another concern is grounding techniques. Ground loops are a nasty problem to troubleshoot.
     
    Last edited: Nov 23, 2007
  3. chesart1

    chesart1 New Member

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    I've seen people use an electric drill to twist two wires together.
     

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  5. Salgat

    Salgat New Member

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    I wouldn't recommend putting any components, such as a resistor, over an IC. When doing prototyping, sometimes ICs burn out, and trust me it's horrid trying to replace ICs that are buried under other components.
     
  6. 3v0

    3v0 Coop Build Coordinator Forum Supporter

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    When breadboarding the ability to trace wires is important. A few words about neatness in routing wires would be a good addition. Even when shown neat examples some students tend to end up with a mess.

    Maybe a bit about choosing where to place/group parts.
     
  7. kchriste

    kchriste New Member Forum Supporter

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    I'd also add:
    Avoid wires that are too large. ie: don't force a lead into the hole. The wire size on a 1N4001 diode is about the max size that a breadboard can accommodate. Solder small gauge pigtails onto larger leaded components such as trim pots.
    Avoid high currents on the breadboard. Keep it below 500ma.
    Turn them 90 degrees to each other. It's not perfect, but then a breadboard isn't exactly a crosstalk free zone either. ;)
     
  8. jfs

    jfs New Member

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    In terms of powering the breadboard, is battery not to be considered ? I have soldered some banana jacks to a 9V battery clip, thinking I could easily power up and down using the binding posts (banana into binding posts, small wire from bottom of binding post to power rails). It's not working. When I measure my battery at the tip of the banana jacks I get a reading of 8,6. At the power rails 0.56.

    Are the binding posts too much resistance for small current ? Should I plug directly to the power rails ?

    Thank you
     
    Last edited: Nov 29, 2007
  9. felis

    felis New Member

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    Binding post resistance is small. Double check your connections, especially in the place where your power rail wire goes to the small hole in the side of a binding post.
     
  10. kjennejohn

    kjennejohn New Member

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    Hi. As for the power supply to use, I suggest you get one something like in the picture. This is a three output supply. It provides a fixed 5V output good for 4 Amps and two variable supplies adjustable from 0 to 24V, 0 to 500mA. The variable current means it will limit the amount of current suppled. When you go over the set amount it will start to adjust the associated voltage downward. This means you get the same amount of power out, but less voltage. When you hit any supply's current limit (4A for the fixed 5V on this unit) a red light comes on.

    This particular unit was on Ebay for a starting bid of $20, with $20 shipping. New units from B&K in this category go for ~$450. The seller was an auction house that couldn't say if the unit was working properly, so this may have been a bad buy. That's the way it is on Ebay. I searched using "output power supply". I used "output" because these can be called "multiple output", "multi-output", "triple output" ... a host of possibilities, but "output" is the common term used. They had other units, many from big name companies like Tektronix and Agilent, going up to $250.

    Perhaps a more realistic way to go is this plug-in switch-selectable 5V/3.3V power supply kit from Spark Fun Electronics for $10:
    http://www.sparkfun.com/commerce/pro...roducts_id=114
    Of course you have to know how to solder, but it looks easy enough. I include a picture. Buy two. When done building them, plug in one set for 3.3V, the other for 5V. These have ON-OFF switches, a nice touch. They also offer wall warts to go with these for $6. Not a bad price.

    Here is their page of prototyping stuff, sort of an "all things for breadboarding":
    http://www.sparkfun.com/commerce/cat...hp?cPath=53_55
    And a page of breakout boards (plugins and adapters) that allow you to use various connectors and chip(sets) you can't find typically in DIP form:
    http://www.sparkfun.com/commerce/cat...s.php?cPath=20

    I hope all this helps you.
    Happy holidays!
    kenjj
     

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  11. Pommie

    Pommie Well-Known Member

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    I whole heartedly agree, I think a little more time spent wiring can save a lot of time later finding problems. I build my boards like this,
    [​IMG]

    Mike.
     
  12. mvs sarma

    mvs sarma Well-Known Member

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    Hi Mike, the patience level you have acquired is really appreciable.

    while the breadboard is fine for learning, the intercapacitance between thstips poses a problem for high freq circuits- a known factor.
    I feel it is time that it colebe redesigned with minimal capacitance and does serve the same purpose or better ,if new functions added. leke a place for putting few smd components by conductive sticking method?

    Hope that the original manufacturers do some research on this.
     
  13. Pommie

    Pommie Well-Known Member

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    People over estimate how long it takes to build a neat circuit on a breadboard. The circuit above was built in a morning. The code that it is running has taken about a month.

    I have never had a problem with capacitance. This is probably because I normally don't go over 20MHz but I have done USB stuff running at 48MHz without any problems. Besides, how much capacitance can there be between 2 strips with a few square mm of area and separated with over a mm of plastic. I really think the capacitance problem is very overstated. Maybe someone can work it out, 40mm² area and 1mm of some plastic (say polycarbonate - Relative permeability 2.8). The long strips are intended for supply and capacitance is always a good thing there.

    Mike.
    Edit, I was curious and so I worked it out. I get 1pF. Completely irrelevant unless your building RF circuits. For the curious I did (8.85*10^-12 * 2.8 * 40*10^-6)/1*10-3
     
    Last edited: Dec 2, 2007
  14. 3v0

    3v0 Coop Build Coordinator Forum Supporter

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    FWIW:

    Some breadboards come with an alu plate that can be used as a ground plane.

    The only real problems I have had is with crosstalk. Using twisted pairs fixed the problem.
     
  15. Hero999

    Hero999 Banned

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    40mm²?

    I would say the area is far greater than that, if the clips are 3mm deep and 60mm long that would make 180mm² which is 4.5pf which is 353:eek:hm: at 100MHz.
     
  16. Pommie

    Pommie Well-Known Member

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    The ones that are 180mm long are the power rails and as I said earlier, capacitance is actually helpful in this case. The connectors used for the actual circuit are 10mm long. I estimated 10mm x 4mm.

    Mike.
     
  17. mvs sarma

    mvs sarma Well-Known Member

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    Thanks to all . The info on Inter connector capacitance of breadboards has cleared some doubts bogging me earlier. As far as digital and microcontrollers are concerned, we can verywell use without apperhension. Mike has already shown a jumbo of breadboarding. Such jumbo boards are being sold presently in India at approx $20/-
     
  18. Funny NYPD

    Funny NYPD New Member

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    Those bread board here in the US is really expensive, big ones cost over $100.Smaller ones about $20.
    Quality are good. And Made in USA.
     
  19. wmmullaney

    wmmullaney New Member

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    I saw one at an e-shop for $7.

    My breadboard is weird, the power rails aren't split like others I'v seen.
     
  20. kavinele

    kavinele New Member

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    Thank you very usefull.
     
  21. 3v0

    3v0 Coop Build Coordinator Forum Supporter

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    Pololu has a good buy on the 830 tie point BB at $5. Three of these make a very nice setup. Move the 2 extra power rails to the top and bottom[​IMG]
     
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