Oscilloscope probes are not convenient for measurements involving solderless breadboards
Part of breadboarding a circuit involves connecting the prototype to external test equipment such as an oscilloscope or function generator. This often involves the use of dedicated probes or alligator clips with awkward connection to the board.
It’s not that the probes are difficult to use. Instead, they aren’t conducive to breadboard use. Personally, I can’t tell you how many times the oscilloscope probe has pulled the component under measurement out of the breadboard. This consumes precious time as the components are reinserted. It consumes even more troubleshooting time if a mistake is made reassembling the circuit.
An alternative is to use twisted wire and a Banana-to-BNC adapter
One clever solution is to use a Banana-to-BNC adapter as shown in this picture. The assembly consists of the adapter itself and a twisted pair of 22 AWG wire. One end of the wire pair is connected to the breadboard. The other end is held in compression between the small hole and the screw collar. The result is a clean connection that will not wrench parts out of the breadboard.
Frequency, voltage, and current limitations
Know that this “probe” has its limitations. It acts like a traditional 1X probe and may load down the device under test resulting in inaccurate measurements. Also, while the wire twist helps, the wire isn’t as effective as a coax cable. Antenna reciprocity suggests that signals will leak into and out of the system. Consequently, the solution is not suitable for high frequency radio frequency work. However, this high frequency limitation is implicit to the breadboard itself.
Tech Tip: The 10x oscilloscope probe is designed for high-impedance to minimize circuit loading. This contrasts sharply with a direct connection especially if your oscilloscope or spectrum analyzer features a 50 Ω. This low impedance is a trap for novice technician and engineers as the low-impedance applied to the Device Under Test (DUT) will cause it to malfunction.
Safety
Finally, there is a safety consideration that applies to all non-touch-safe banana connectors. They are not suitable for high voltage connection as the picture clearly shows exposed metal that presents an electrocution hazard to personnel. Once again, we find that the breadboard itself has voltage and current limitations.
Let’s be clear. Do NOT breadboard high voltage circuits. We know that breadboard wires routinely become unseated. There is all too human tendency to reinsert the wire exposing the experimenter to an electrocution hazard. A much safer alternative is provided using DIN rail mounted terminal blocks.
Tech Tip: The term “touch safe” as used in this article refers to a class of insulated banana plugs and accessories. A classic example is found on better multimeters where the front panel and the probe connection are insulated. Understand that they are not 100% safe. However, your finger will not be able to touch the exposed conductor.
Parting thoughts
This twisted wire technique complements your solderless breadboard prototyping experiments. The technique generally matches the breadboard capabilities in terms of frequency and current limitations.
On a related note, let’s end with a question: What problems will you encounter if you use a 10x oscilloscope to connect a function generator to your circuit? Why would the twisted wire and BNC adapter be preferred for connection to a function generator?
Best Wishes,
APDahlen
About the author
Aaron Dahlen, LCDR USCG (Ret.), serves as an application engineer at DigiKey. He has a unique electronics and automation foundation built over a 27-year military career as a technician and engineer which was further enhanced by 12 years of teaching (interwoven). With an MSEE degree from Minnesota State University, Mankato, Dahlen has taught in an ABET accredited EE program, served as the program coordinator for an EET program, and taught component-level repair to military electronics technicians. Dahlen has returned to his Northern Minnesota home and thoroughly enjoys researching and writing articles such as this.
Return to the breadboard guide for additional construction tips.