Introduction: How to Prototype Without Using Printed Circuit Boards
When I learned how to build ‘one-off’ projects thirty years ago, I used the "wire wrapping" technique. Back then, I had access to an electronics shop with a $100 wire wrapping gun, kynar wire and a supply of wire wrap IC sockets. At home, however, with limited resources and no wire wrap gun, I had to make do, so I developed a technique that uses perfboard, kynar wire and solder that results in a neat, quick to assemble and very dependable electronic board.
Assuming you've developed your design on a breadboard and made a schematic, the steps to build your circuit board are:
1. Place your components on the circuit board
2. Plan the wiring on the board using a Perfboard Layout Planning Sheet
3. Connect the components using Kynar wire
Step 1: What You'll Need
In addition to the perfboard and a soldering iron, you'll need some fairly common tools and supplies:
Kynar wire: This is an insulated 30-gauge single strand wire. It's a rather thin wire which is useful for low current and low voltage digital circuit connections. I use three colors: Blue for Ground, Red for +, and Orange or Yellow for all the other connections. This wire is also "pre-tinned" so it takes solder very easily.
Wire Cutter, Wire Stripper and Needlenose Pliers: I have a special stripper that is permanently set to strip the Kynar wire. It may take a few tries getting the correct setting, since you don't want the stripper so tight as to nick the wire itself, or so loose that it just slides off of the insulation. A good pair of needlenose pliers are required to hold short lengths of wire when stripping off an end.
0.8mm Rosin Core Solder and Solder Paste: The paste (you can use a rosin pen as an alternative) is useful if you want to flow solder over and join a socket pin, a wire and copper pad quickly and without too much heat.
Tweezers: I have a surgeon's tweezer (the kind you got in biology class in school when you had to dissect that frog) that I use for looping wire ends and a sharper, more precise steel electronics tweezer for holding wire during soldering.
“Helping Hands”: This inexpensive reconfigurable alligator-clip holding device is an indispensable tool when using this prototyping technique.
Reading Glasses / Magnifying Glass / Manual Dexterity: Depending on your age, reading glasses may be of assistance. If you don't have steady hands, you may have difficulty managing some of the smaller, more finicky aspects of this technique. If that's the case, printed circuit boards are probably a better choice.
Step 2: Place Your Components on the Circuit Board
In this example, I'm using a 7 x 9 cm perforated circuit board from Seeed Studio; this board has numbers and letters on the top side indicating the columns and rows, and round copper solder pads around each hole on the back side. The letters and numbers come in handy when planning the wiring (Step Two), but any perfboard can be used as long as it has copper pads for soldering. I have also used stripboard with this technique, but it requires that you to cut the copper strips and letting the kynar wire carry the signals, defeating the purpose of the strips.
You should place your components to minimize the length of wire required. This will reduce the possibility of stray capacitance wreaking havoc with your circuit. To further deter parasitic voltages, place one .01 uf capacitor across the + and Ground beside each integrated circuit that you use in your design.
To hold the components in place, you can bend the pins outward slightly on the back side, or you can use a dab of quick setting glue on the front of the board. If you use glue, don't use it on the wire pins or you may not be able to achieve a secure and dependable electrical connection. Eventually you will be soldering each component onto the board, you so don't need a lot of glue, just enough to keep the component from falling off of the board during assembly.
Note: Use IC sockets whenever possible. Try to avoid soldering integrated circuits onto your board, and if you use sockets, make sure they are empty during assembly. Some ICs use CMOS technology that are very sensitive to static electricity charges.
Step 3: Make Your Wiring Plan
This stage is crucial. The time and care you take in this step may be the difference between a circuit that works and one that doesn't.
I've developed a wiring planning sheet (attached) that is a modification of the Meccano stripboard planning sheet. Feel free to share it with your friends.
The planning sheet will represent the back of the perfboard, where you will do all your wiring. Because it shows the back side, it is a backwards mirror-image of the front of the board. This is where the numbers and letters are helpful on the front of the board, to help you navigate this mirror-image world of the circuit back side.
Correspondingly, there are numbers and letters on the planning sheet, arranged inverse to the order on the front of the perfboard. Use the following steps to create an error-free wiring plan:
1. Use a pencil to fill in the holes for socket pins and component wires. Check and re-check the placement. I find that once I have reliably established one component on the board, I can count across or down a certain number of holes to locate the next component.
2. For IC sockets, name the IC and number the pins. Remember that pin numbering on the back side needs to be done in a mirror-image compared to front side pin order.
3. Refer to your circuit schematic: Draw lines to connect the + and Ground rails to the components. On my perfboard, there are large pads along the right and left sides, and I use these for + and Ground.
4. Refer to your circuit schematic: Draw wires for all the other connections. Try to avoid having more than two wires connect to a pin or a component; there is a limited amount of space on a pin for wire connections.
Step 4: Connect the Components Using Kynar Wire...
This step is actually repeated for as many times as you have wires to connect. The process is straightforward:
1. Strip the end of the wire about 2mm
2. Measure the length of wire required
3. Strip the other end
4. Loop the bare wire ends
5. Place the loops around the pins or component wires
6. Crimp them so that they provide a temporary hold
7. Solder the connections to make them permanent
It's time to turn on your soldering iron and clear your workbench.
Affix your circuit board, back side up, to the helping hands tool.
In the next steps we will deal with each step in detail.
Step 5: Measure and Cut the Wire
Use the planning sheet to determine what connection to make.
Before cutting the wire, strip 2mm of insulation from the end.
Line up the wire on the perfboard so that it extends from one connection contact to the other to get a sense of how much wire you'll need.
Add about 5mm extra length, cut the wire and strip off 2mm of insulation.
You now have a wire with 2mm stripped off both ends.
Step 6: Make Loops Around the Wire Ends
Using the end of a pair of tweezers, make loops over the bare ends of the wire and fit them over the pins or component wires. If you have other wires already soldered in place, you may find it helpful to feed the wires underneath the existing wires; this method will help you hold the new wires in place before you solder them.
Step 7: Crimp the Loops Over the Pins, Then Solder Them
Use tweezers to crimp the loops tightly around the pins. The connection only needs to last as long as it takes to apply the solder.
If more than one wire is to be connected to a pin, you have a choice:
a) Do the same as above, crimping a second loop to the same pin and then solder both wires to the pin.
b) Solder the first wire to the pin. For the second wire, don't loop it, keep it straight. To connect it to the already soldered pin, dip the end of this wire in some rosin paste (to clean it and encourage the solder to bind to it). Re-heat the solder on the pin and push the wire onto the molten solder.
If you use soldering paste, avoid using too much. The paste residue can carry current which, unless removed, can wreak havoc on your circuit. You can use a toothbrush with isopropyl alcohol to remove excess flux.
Step 8: Testing Your Work
Repeat steps 5 - 7 until all your connections are made. As you proceed, you may find it useful to complete one component (such as an integrated circuit) and then start on another. This enables you to test each component as you build it.
My blog has examples of other projects that use this technique.
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