Solderless (well, almost) homebrew electronic projects
by Lyle Koehler, K0LR
Introduction
This article describes how to use solderless breadboards, which can overcome some of the problems of dealing with today's tiny components, and which provide a quick and easy way to build or modify home brewed circuits. I will start with a description of what solderless breadboards are, and then provide construction details and/or schematics for sample projects that lend themselves well to solderless breadboarding. More projects will be added in the future.
About solderless breadboards
Solderless LowFER transmitter
MF Transmitter
LF Converter
HiFER Transmitter
About solderless breadboards
Solderless breadboards are great tools for the experimenter. They provide the closest thing to instant gratification that you are likely to find in electronic circuit construction. Component leads are plugged directly into holes in the board, where spring clips make electrical connection to the leads and also hold the components in place. The boards come in a variety of sizes, from about 2 by 3 inches up to 7.5 by 7.5 inches. The smallest boards will hold up to four 14 pin dual inline packages (also called DIPs), and the larger boards can hold 30 or more DIP integrated circuits. The holes in the board will accomodate wire sizes between number 20 and number 28, corresponding to diameters between 32 thousandths of an inch and 13 thousandths of an inch. It takes about a quarter of an inch of bare lead inserted into the hole to make electrical contact. If a component has leads that are too big, too small or too short, I simply solder pieces of the proper size wire to the leads. I know, the boards are supposed to be solderless, but you can't have everything. Excess leads clipped from resistors and capacitors used on previous projects work well for this purpose, as well as when you need short jumpers between points on the board. Larger boards come with plastic or aluminum back plates and with two or more binding posts for attaching wires from external circuits. Of course, you can attach a wire of the correct size to any hole in the breadboard, but they will pull out if you put too much strain on them.
It may seem that solderless breadboards are not suitable for RF applications, or that with so many spring contact connections, they must be unreliable. I wouldn't use one for a high performance VHF rig, or for the life support system in a manned space vehicle. However, they work pretty well through the HF range, and at least for simple circuits, contact failure is not likely to be a problem. Most of the circuits and subcircuits used in my homebrew construction projects are first checked out by building them on a solderless breadboard. There is nothing to stop you from putting a finished solderless circuit in a box and using it as a "permanent" piece of equipment, as I have done on more than one occasion.
Solderless breadboards vary in price depending on size, brand, and where you buy them. The largest one available in Radio Shack stores normally costs about $22, but I've seen them on sale at for about $12.50, and vendors like Jameco Electronics have similar boards for about the same price. Jameco's largest board costs about $31, while the same size board in other brands or from other vendors can cost 65 dollars or more. Boards are also available as part of experimenter stations with built in power supplies and a variety of other "bells and whistles" at prices of several hundred dollars.
The description that follows is for a generic, small solderless prototyping board like the Jameco JE21 (about $5 each) shown in the photograph below. Larger boards use the same basic layout except that they are longer, and two, three or four of them are stacked side by side. Just above the bottom of the board there are two lengthwise rows of holes. Actually the rows of holes aren't continuous; for some reason they are arranged in groups of five with a gap between each group. However, the holes in each lengthwise row are connected together inside the breadboard, so that they can be used for connections such as power and ground that are shared with many components in your circuit. Later on, I may refer to these lengthwise rows of holes as the bus strips, or the power and ground buses. On longer boards, the bus strips are often split in the middle so that they can be used for different connections on the left and right halves of the board. I usually find this more of a confusion factor than a benefit, so I run jumpers across the gaps as soon as I start a project. Sometimes I forget, and wonder why there is no power or a bad ground connection to some of the components. There is usually no marking to tell you that the left and right halves of the bus are not connected, except that there is a larger gap between the middle groups of five holes than the others. Jumper wires must be installed across the gap if you want the same bus to run the entire length of the board.
Jameco JE21 breadboard (actual size 2.1 by 3.2 inches)
Above the bottom two rows of holes, which make up the bus strips, there is a gap, and above that there are 5 rows of holes on a uniform 0.1 inch grid spacing, running the entire length of the board. However, instead of being connected internally in a lengthwise direction like the bus strips, these holes are connected together vertically in groups of 5. Suppose we plug an integrated circuit (we will shorten that to IC) into the breadboard so that it straddles the big groove in the middle. The spacing of the holes is arranged so that the leads on a standard 14 or 16 pin IC package will fit into the first holes on each side of the middle groove. Since the holes are connected together in groups of five, that leaves 4 available points to connect other components to each pin on the IC. What if more than four things need to be connected to one IC pin? You run a jumper wire to an unused group of holes somewhere else on the board and expand from there.
As mentioned earlier, the board is symmetrical, and the same patterns we have already described are repeated above the middle groove. To summarize the board description, starting from the top there are two lengthwise rows of holes connected together internally (but the two rows are insulated from each other). Then there is a gap of smooth plastic. Below that, there are 5 lengthwise rows of holes that are connected together vertically in groups of 5 (but every group of 5 vertical holes is insulated from all other groups). Then we come to the large middle groove, 5 more rows of holes, a gap, and finally two more rows before the bottom of the board. If you have an ohmmeter or audible continuity checker, it might help to connect a couple of small wires to the test probes and literally poke around in the board, getting familiar with its internal connection pattern.
There is no special trick to inserting component leads or jumper wires into the board. However, the ends of the leads must be clean, smooth, bare and straight for at least one quarter inch. You also need to make sure that the wire is inserted straight down into the hole; that is, perpendicular to the board surface. Sometimes a component lead or the hole will be stubborn; in that case make sure the lead is straight and without any burrs on the end. I often have to squeeze the leads gently in the jaws of a needle-nose pliers to remove any little kinks, especially on used components from my junkbox. It helps to grab the lead just above the insertion point with a tweezers or needle nose pliers so that it has less room to bend as you try to push it into the hole. It is important for RF circuits to keep leads as short as practical (not necessarily as short as possible). Keeping them short also reduces the chances of two bare component leads touching each other. For most small components and short jumper wires, I try to bend the leads to fit the desired hole spacing, and then insert both leads at the same time. This usually works better than leaving the wires long enough so that you can insert one end first and then the other. But whatever works for you, as they say. Often you have no choice in the matter, as is the case with integrated circuits where you have to insert 14, 16 or more pins essentially all at the same time.
Integrated circuits usually come with their leads spread out slightly, so that you have to bend them inward a bit to make them fit the hole pattern. The same thing is true when you try to put an IC into a socket or insert it into a conventional soldered circuit board. If necessary, I bend the pins by grabbing the IC firmly by the ends (I have small fingers; it might be harder for other people). Then I hold the IC so that the top of the plastic case is vertical and push the leads down gently against a horizontal flat surface. The idea is to get the leads to line up perpendicular to the top of the IC package, with the leads on each side parallel to each other. 14 or 16 pin ICs are not too hard to insert. Usually this bending operation is not necessary on breadboards; you can take the ICs just the way they come from the supplier and use your fingers to encourage the pins to go into the holes in the board, but you do have to be careful not to mash any of the pins. It gets tougher with 28 or 40 pin ICs; fortunately I don't deal with them very often. Once an IC has been inserted correctly in a breadboard or IC socket, the pins are pretty well aligned and it is easy to remove and re-use them. That's one beauty of the solderless breadboard. If you don't like the way the circuit works or simply get tired of it, you can pull out the parts and use them to build something else.
Notes on using the bus strips at the top and bottom of the board: I usually use the inner bus strip (the upper one) at the bottom of the board for the ground bus, and the inner strip at the top of the board for power. This helps me build a circuit from a schematic, because schematics tend to show the power connections at the top and the ground connections at the bottom. However, quite often you will want to connect a lead on the top of the board to the ground bus, or a component on the bottom of the board to the power bus. If you don't need the remaining two bus strips for any other connections, connect the outer bus on the top to ground and the outer bus on the bottom to power, so that both buses are available on each side of center. An example of a larger breadboard with the power and ground buses connected in this way is given in the photograph below. Note that this breadboard has two vertical bus strips on either end of the board. I have connected one set of the vertical strips to two of the binding posts and used them to distribute the power and ground connections to the horizontal buses. Also note the orange jumpers that bridge the gaps in the middle of the horizontal bus strips.
3M Solderless Breadboard with power and ground jumpers installed
Many suppliers of solderless breadboards also sell pre-cut jumper wires in various sizes. Somehow they never seem to be the right size, so I find it more effective to make my own. I have often made jumpers from the insulated #26 solid copper wire found in multi-conductor telephone cables. However, the #26 wire is just a little bit flimsy, and something like #22 or #24 is better. Radio Shack sells a three-roll set (three colors) of #22 insulated solid wire as catalog number 278-1221. Bare tinned bus wire is also good for jumpers, as long as they are very short and in locations where there is a low risk of the bare leads touching each other. When trimming excess lead lengths from components such as resistors and capacitors, I often save the pieces of bare tinned wire and use them for short jumpers.
Various techniques can be used for connections to the outside world and to circuit components like switches, connectors and potentiometers. Since most of these off-board components are fairly easy to work with, soldering one end of a jumper wire to the component should not present a problem. Another option is to use a clip lead for the connection to the component, with the other end of the clip lead attached to a short bare wire that is plugged into the breadboard. To provide a somewhat stronger connection, it helps to bend the bare wire into a U shape and plug it into two holes in the breadboard; then connect the clip lead to the exposed center of the U. Other techniques like crimp connectors, screw terminals, wire nuts, etc. can be used if you really have an aversion to soldering. On larger solderless breadboards with backplanes and binding posts, you can attach leads to the binding posts and/or drill additional holes in the protruding portion of the backplane to mount connectors, switches, etc. A metal L shaped bracket, attached to the bottom of the breadboard with double sticky tape, can serve as a mounting point for external connections and a temporary (or permanent) front panel for your project.
What if you want to re-build your project in more permanent form, but don't want to go to the trouble of laying out a PC board? I have seen pre-etched and pre-drilled project boards that have the same hole layout as solderless breadboards, so that the project can be transferred directly. Being too cheap to buy those exotic boards, I normally use the little project boards from Radio Shack like the one shown on the left. Its layout is similar to the solderless breadboard except that there are fewer connection points, and the buses used for power and ground run down the middle of the board rather than along the outside edges.
Solderless LowFER transmitter
The LowFER transmitter described in this article is shown built on a Jameco JE21 solderless breadboard that is about 3.2 inches long and 2.1 inches wide (a larger breadboard will also work, of course). This transmitter circuit is similar to the "Simple LowFER Transmitter" described elsewhere on my web page, but it uses an Epson programmable crystal oscillator module. The Epson module offers an inexpensive way to get a custom crystal AND the oscillator circuit all in one compact package. These oscillators are a little noisy for use in HF circuits, but when divided down to the LF region, the phase noise is very low. In this circuit, an oscillator operating at approximately 1.8 MHz is divided down by a factor of 10 in a 74HC4017 integrated circuit, which in turn drives a complementary pair final amplifier. The final amplifier will handle the 1 watt FCC Part 15 power limit for operation in the 160 to 190 kHz region, and will provide an efficiency in excess of 80 per cent when driving a 50 ohm resistive load.
A completed breadboard transmitter is shown in the photograph below. The Epson oscillator module is in the mini-DIP package at the left of the protoboard. It oscillates at its specified frequency of 1.8373 MHz, and I marked it with a piece of tape so that it wouldn't get mixed up with other Epson modules in my collection. The oscillator module has four pins: power, ground, output, and output enable. In this photograph, nothing is connected to pin 1, the output enable pin. It has a high-resistance internal pullup, so that the output is enabled as long as pin 1 is left open, and disabled when pin 1 is pulled to ground through an external circuit. To key this transmitter, I would connect a 10k protection resistor between pin 1 and an external keyer such as the PC beacon identifier described elsewhere on my web site. Note, however, that a conventional ham keyer that pulls a keying line to ground for the "key-down" condition will require an inverting circuit. Some keyers (including the PC beacon keyer) offer the option of "normal" or "inverted" keying. If you simply want to try the transmitter with a good old fashioned straight key, connect a 10k resistor from pin 1 of the oscillator to ground, and connect the straight key between pin 1 and +5 volts (pin 8 on the oscillator package -- pins 2,3,6 and 7 do not exist).