Electronic Tricks and Hints, Imaginnering Got Ideas?, Imagineering On-Line Magazine

There are two basic bread boarding methods that I have used over the last 30+ years. One method uses lots of IC sockets that are designed for pin to pin wire-wrapping methods and uses minimal hand soldering. The other method uses pins pushed into a perforated board and requires that every lead of a component be hand soldered to a pin. I suggest that you use wire wrapping methods only when they are justified. Wire wrapping should be considered when the design calls for a large number of logic ICs that can easily be mounted on a perforated board with plenty of room between ICs. Wire wrapping methods should not be used for high frequency, medium power, low level signals or designs that call for a large number of discrete parts. If the basic circuit design is not clear, I suggest that you first test and refine the circuit using a solderless breadboard system. Such systems allow components to be quickly changed and additions made. A circuit can usually be assembled and tested on a solderless breadboard system in about one tenth the time it would take to hand solder the same circuit. Using the solderless breadboard, you can make sure the circuit functions properly before you solder the parts together on a breadboard.

In either method, I recommended that the circuit be elevated off the table to prevent components and pins on the bottom of the board from touch a metal table top. If you use a wire wrap technique, you will need at least 3/4 inch space under the board. Hand soldered board may be able to safely use 3/8 or ½ inch spacing. 1/4 inch diameter metal standoffs of appropriate length mounted in each corner of the board is a great way to keep the circuit bottom off of the table.

In hand soldered boards, some care will need to be taken to insure a successful outcome. When there is sufficient board space, layout the resistors and diodes in a horizontal manner. Try to position the circuit components in a neat right angle configuration. Don't put components at funny angles unless you absolutely must. Use easy to solder Vector solder pins whenever possible to allow for component value changes without disturbing the underside wiring. Always use IC sockets. Never solder the components directly to an IC unless circuit size is a concern. Blown ICs are difficult to remove when there are a dozen parts soldered to them. Always solder the IC socket completely first, then install the ICs into the sockets when the whole circuit is finished. If the ICs are loaded into the socket during the soldering process problems may result. The heat from the soldering iron can cause the ICs to be damaged or to be glued into the sockets.

Do all your soldering on the bottom of the board if possible with all the components on top. Don't zig-zag wires through both sides of the board. It is a lot easier to trace the wiring when all the connections are made on one side, even if many insulated wires cross over each other. Use bare 28ga tin plated wire for most of the low current connections but shift to larger size wires as needed. Some long power and ground wires should be increased to 24ga or 22ga. High temperature insulated 28ga wire ("Tefzel" from Vector) is ideal for connections that must cross over each other. You might find it easier to use some thin teflon sleeving on some short wires around ICs. 28ga high temperature wire-wrap wire is also good for long connections that have to snake through and over other components. Remember, load the ICs into the sockets after all the wiring is done. White plastic IC pin tags (From OK tool) are great to keep track of the IC pin number when soldering the bottom of the board. If you don't have the tags, circle pin number 1 on the circuit board bottom with a waterproof felt tipped pen. Then, at least you will have some reminder of the IC pin numbers when soldering. Have a copy (not the original) of the schematic close by and mark it with a yellow marker as you wire up the connections. You should also double check each connection after you have finished soldering.

Always mount the ICs so they all point in the same direction (pay attention to the dots or markers on the IC sockets that indicate where pin 1 is) Some IC orientations can be rotated 90 degrees from the rest but there should never be more than two orientations on any one circuit board and they should not be no more than 90 degrees from each other. If time permits, try to imagine how the circuit might be arranged when turned into a printed circuit board and try to mount the components in that configuration. Such initial extra efforts will speed-up the tasks of making a printed circuit board artwork and can be justified. Otherwise, be neat but not perfect. If you are making a breadboard that will later become a printed circuit board, then pay more attention to the layout. The layout should be sensible with little or no jumpers and wire crossovers. However, don't try for perfection. Remember, you are only approximating the final look of the finished printed circuit product.

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USING VECTOR PINS

Always try to install the Vector pins so they face each other with the rounded side facing away from the inside. A Vector pin insertion tool will speed up the process. When properly oriented, the pins can be positioned within 0.1 inch of each other in a sidg-by-side or back-to-back orientation. A general rule of thumb is that two Vector pins will take up about 0.1 inch more space than the component would otherwise need, if it were soldered into a printed circuit board. Most 1/4 watt resistors should use a 0.5" spacing with the two Vector pins facing each other. If the 1/4 watt resistors are mounted vertically, plan for 0.2 inch spacing between pin centers. Once the pins have been installed, the components can be soldered in place. It may be easier to first decide where the components are to be placed on the circuit board, then install the Vector pins for a group of components before soldering the components into the pins. Cut the resistor leads so the leads just barely poke out the end sides of the pins. The exposed lead ends will make removing the component easier. If several parts are to be connected, say to a transistor, then try to mount those parts near the transistor. If a resistor is to be connected to pin 1 of an IC, then mount that part close to pin 1. Such positioning allows short bare wires to be used to make most of the connections. It may also be easier to save all the major power and ground connections until last while concentrating on the other point to point connections.

Mount typical TO-92 transistors in a "OOO" pattern with 0.1 inch between pins. Try to install the vector pins so little component lead shaping is needed. Capacitors that would normally need 0.2" lead spacing can be installed into Vector pins without bending the leads, if the pins are installed with 0.3 inch pin center spacing. During soldering, fill one pin with solder first then insert one component lead into the pin while the solder is still liquid. Then, after the first lead is secure, the second can be soldered. Resistors can usually be first cut to length then placed into the "V" part of the pins and soldered.

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SOLDERING TECHNIQUES

When soldering multiple Vector pin connections together, use a looping daisy-chaining technique with a single wire. Start the process with one of the components at one end of the chain. Bend the end of the bare wire so a small hook is formed. Place the hook around the Vector pin and use a pair of pliers to crimp the hook around the pin. Then go to the next pin, loop the wire around the pin and go on. If properly positioned, several components can be connected together using such a technique in just a few seconds. At the end of the chain the last wire is tightly looped around the pin and the wire is cut. Before soldering the individual pins or wire connections, make a quick inspection and make sure the wires are not touching other pins or wires. Some wires may have to be crimped slightly to insure a good contact. When all the connections in the chain are done, you can finish soldering all the pins. If the chain needs to be later connected to more components, it may be a good idea to leave one of the end pins unsoldered to remind you that there is still a connection to be made. If just two pins have to be soldered together, use a figure "8" two loop pattern using the initial hook connection on the first pin.

Installing IC sockets in a standard Vector board can be difficult unless a few tricks are used. Use the connection to a nearby component or, in some cases any IC pin to pin connection, as a way to hold the socket down on the board. Prepare the wire hook as discussed above and solder it to the nearby component first. Then, while holding the IC in place with one of your left hand fingers, loop the wire end around the IC pin, cut the wire and solder the wire onto the pin. You will have to either use a device that can hold the solder near the pin/wire junction during the soldering process or develop a technique of using some of your other fingers of your left hand, while still holding the IC socket in place, to position the solder next to the pin. Once the first IC socket solder connection has been made the socket should stay in place for the remaining connections. Other techniques for securing the IC on the board using super-glue or hot-melt glue are not recommended. The glue can seep into the socket to produce a poor connection to the IC.

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Reminders:

Always leave some extra room on the circuit board if the overall size is not a concern. It is a lot easier to add extra parts later when there is room. Figure about 30% extra space for a given circuit.
Always label inputs and outputs that will be connected to external components. Some adhesive backed white label paper is great for making little labels. A little fingernail polish can be used to hold small labels in place.
Always leave about 0.3" spacing at the board edges.

OTHER COMMENTS FOR STANDARD THROUGH-HOLE CIRCUITS

In most of the circuits I design, very little power supply decoupling is needed. Usually one 10uf aluminum capacitor or two 0.1uf ceramic capacitors across the supply (+ to -) (one on each side of the power supply bus) is all that is needed. If specific supply decoupling around ICs is needed it will be shown on the schematic.

Unless it is called out on the schematic, it is assumed that standard 1/4 resistors and 1N4148 diode are used. Larger sizes or other types will be called out on the schematic.

Remember, when the schematic calls for two components to be wired in series, such as a fixed resistor and a pot, or a capacitor and a resistor, you can always interchange the sequence of the components with no change in operation.

Use 0.5" spacing between vector pin centers for standard 1/4 watt resistors and 0.4" for the diodes. If necessary, you can go as close as 0.4" for the resistors and 0.3" for the diodes if space is a concern. In some designs you may have to stand up the resistors and diodes. That is OK. If standard resistors or diodes do have to be mounted on their ends install the Vector pins with 0.2" spacing so they face each other. Larger parts, like big capacitors, should not use vector pins, but be directly soldered to the circuit.

You will find it easier to load the vector pins in first, then solder the bottom of the circuit, before you actually load the pins with components. That way, you have a relatively flat surface to push against as you solder. If you do load the pins with components, always solder in the components with the lowest profile first.

Use a vector pin when a hookup wire has to be soldered to the circuit board as an input or output. Don't solder an external wire connection on the bottom of the board or through a hole. If connections have to be made to heavy 18ga wires, drill out one of the perf board holes and use the large size (0.062") Vector pins. For the 0.062" Vector pins, a 1/16" drill bit will be needed.

Use a quality soldering iron with a long pointed tip. The tip should be rated for 800 degrees. Believe it or not, less heat is applied to the components with a quick hot smoky flash than an long warm sizzle. Also, be sure to use good solder. In my book, there is none better than Alpha 60/40 in a 0.032" size.

I usually do not show power and ground pin connections on the usual logic ICs or op amps, since they are almost always configured in the same way (upper right hand corner being power and lower left hand corner being ground). I also often do not indicate IC pin numbers on multiple logic gates and devices. I leave off the pin numbers until the complete printed circuit board artwork has been mapped out. If I did select the pin numbers, they may not be the best for the final circuit arrangement. I will provide copies of the IC data sheets and expect the circuit board builder to decide which pins to use in the circuit.

Remember, when using C-Mos ICs, all unused inputs must be connected to either supply or ground.

When soldering certain 1% resistors and some capacitors and diodes, try to solder them so their values can be seen.

It is OK to not to use vector pins on some larger components like big capacitors or resistors. However, keep in mind that a part soldered without a vector pin may be difficult to remove later if required.

Use quality wire when wiring up test fixtures or circuits inside enclosures. Low current paths can use 24ga wire while those wires that may carry higher currents should use 22ga. Try to use color coding schemes when possible. Red is usually reserved for the positive voltage and either black or green is used for ground. It those designs that use a positive and negative power supply (+-15v) green should be used for the ground connections and black used for the negative voltage.

I find it easier to connect all the parts needed for a particular circuit without concerns about power and ground connections. After I have connected the parts I then find the nearest power and ground to complete the circuit.

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CHEAP ELECTROSTATIC DISCHARGE TESTER

Anyone who has ever had a shocking experience on an especially dry day is acutely aware of the kinds of high voltage that can be generated from a simple walk across a carpeted floor. Those same finger to metal sparks can destroy or disrupt sensitive electronic circuits. Good design practices take great care to avoid such a potential disasters by maintaining sufficient insulation between metal or plastic enclosure parts and the electronics within or by shielding any especially sensitive components. But, the only sure way to determine if such measures have their desired effect is to test them. Many high quality and certified electrostatic discharge instruments do exist which can test your product for the worst possible static discharge. However, they are expensive; to buy or to rent. But, you don't have to spend thousands of dollars determining if your product is susceptible to high voltage discharges. An inexpensive device that will work nearly as well as the precision units can be found in nearly any hardware or department store. Remember those piezoelectric propane gas grill lighters? You know, the ones with a long metal neck that you stick next to the burners? Well, with a very simple modification those spark ignites can generate some 15,000 volts, enough to determine if your product has a real problem or not.

Most of the units have a four prong triangle shaped metal piece that is pressed over an insulated center electrode. When the igniter handle is pressed sparks are generated across the electrode and the sharp prongs. To modify a unit for use in static testing first bend or cut off the sharp pongs of the outer metal piece, preventing the sparks from forming. Next, insert a stiff wire about 2 inches long into the center electrode which usually has a soft conductive rubber center. That is all there is to it. Since one side of the internal piezoelectric crystal that generates the high voltage is connected to the handle you may wish to connect a second wire to the metal body. Otherwise, touching the chassis ground of the instrument is usually enough to complete the circuit.

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PHOTOGRAPHIC FILM MAKES INEXPENSIVE INFRARED FILTER

To minimize interference from room lighting, optical communications receivers and some infrared TV camera systems will often place an infrared low-pass filter in front of the light detector. The filters are designed to block most of the visible light, allowing the near infrared light to pass and reach the detector. However, glass filters, that are often used for such applications, are expensive. A cheap alternative is ordinary 35 mm photographic film that has been exposed to fluorescent light and then developed. As shown in the attached figure, the color negative produced after the photographic developing process has a sharp cut-off at about 830 nanometers and completely blocks most of the visible spectrum. The filter's transmission is perfect for many near infrared LEDs and lasers with wavelengths between 830 and 950 nanometers. Kodak Kodacolor film with an ASA rating of 100 seems to work the best. A 5 second exposure to "Cool White" fluorescent light will work do the trick. Have the film processor develop the film in the usual manner but not make any prints. The color negatives become the filter material. A typical 36 exposure roll will cost only about $5.00. The film can be easily cut into any size or shape that may be needed. However, the film is not recommended for applications where it can become scratched or exposed to moisture.

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