This article covers a variety of miscellaneous thoughts regarding printed circuit boards, perf boards, breadboard, soldering and other aspects of assembling a circuit. These suggestions were consolidated into their own article, as they didn’t seem to fit into any specific robot project. So, forgive me in advance if the topics seem to bounce around.
The first trick is something that I now use all of the time.
Unlike off-the-shelf circuits and kits, most hobbyist-created projects are unique and unproven. Therefore, considerable time is devoted to testing, fine-tuning, and perfecting them. Part of the process usually requires hooking up a multimeter or oscilloscope to the circuit board to take electronic measurements.
Most hook test probes have an adequate grip to stay connected to a single pin or wire. But, when numerous probes are crammed against each other, one or more of the hooks inevitably pop free.
A multimeter test probe hook firmly attaches to a loop of wire.
On your circuit board, simply place two holes for any point that you are likely to need for measurements. Such as battery input, regulated voltage, GND (ground), sensor/analog signals, frequency generators, bus pins, and so on. Then, solder a loop of wires across those two holes.
The board now has a reliable and secure test probe connection point for almost no cost! Also, notice that the end of transistors, diodes, and resistors already provide a nice place to hook a test probe.
Through-hole resistors can take up considerable space on a solderless breadboard or circuit. Fortunately, these resistors often provide a convenient path for signals to pass underneath. But, occasionally resistors simply take up precious space and complicate the routing of signals.
The following image is from the Debounced Counter project. The 7447 chip drives current to the numeric LED. But, the LED segments need resistors to protect them against too much current.
Inline resistors save space on a solderless breadboard.
In this case, one end of each resistor is pushed into the solderless breadboard, while the other end of each resistor has a wire soldered to it. The other end of the wire connects to the appropriate LED segment.
Here is an example that follows a similar pattern.
Robot circuits often include two-pin connectors driven by transistors or H-brides. Motors, speakers, relays, or other devices are usually attached to these connectors.
A simple way to silently and safely test these connectors is to attach a bicolor LED with a resistor. The LED turns red when provided a positive/negative signal and turns green when provided the opposite polarity (negative/positive). And, of course, the LED turns off if both pins have the same voltage
The LED doesn’t require much current, so it is unlikely to damage an untested circuit by pulling too much current. If you choose a large enough resistor, the LED won’t likely be damaged by a moderately higher-than-expected voltage. Moveover, the LED won’t roll off your desk and put a divot in your hardwood floor, like a motor will.
Make a bunch of these for populating your circuit boards for their first smoke tests. Then, slowly swap them out for the actual destined component as you gain confidence in the functionality of the board.
Speaking of two-pin connectors, here’s a trick to protect your delicate fingertips when you solder a connector to a PCB.
It is important that the connector lie flat and square against the board during soldering. Otherwise, not only will the angled connector look unprofessional, but also it will rock against the board when the cable is attached and removed. Eventually, the board holes will wear out or the solder bond will crack.
A tall yellow shunt (pictured at right) keeps fingers from getting pierced or burnt while soldering a Molex connector.
Rather than pushing down on the connector points with your finger, use a spare shunt to insulate yourself from the sharp ends and from the heat. This doesn’t always guarantee that the connector angle will be perfect, but it does make it easier for you to be patient.
The folks at SparkFun Electronics recommend slightly staggering every other pin of your connector when designing your circuit board. This allows the connector to be pressed firmly into place without needing it to be held during soldering. Unfortunately, their trick doesn’t work for boards you’ve already made (or obtained elsewhere), nor does it work for connectors that have fewer than three pins.
Next, we'll look at preprinted circuit board patterns (perf boards). Lastly, we'll see how an alligator clip can help us solder and how we can keep their barrel ends from being squished.