This is a first posting in a blog series supporting a RoadTest Review of PicoScope 6424E Oscilloscope.
While waiting for a replacement oscilloscope (PicoScope 6424E Oscilloscope + Accessories: The Application ) to substitute for the unit shipped in error, I figured I would unboxed the Pico Probe Positioning System and establish an oscilloscope testing platform using a Pi.
Part of the reasoning for creating this blog post was to satiate my desire to get on with the RoadTest. Knowing I would have to wait a few more weeks to get the oscilloscope equipment made me antsy. The delay provided me an opportunity to slow down and spend some time investigating items outside of the oscilloscope.
The User's Guide provides a pictorial (shown later) of the kit parts along with insulation washer installation instructions and how to use the gear. The insulated washers are placed on the upper and lower surfaces of the spring loaded magnetic PCB holder. They prevent the metal surface of the holders from coming in contact with the printed circuit board (PCB). The majority of the kit is metal. Metal holders PCB and probes all sitting on a metal base.
The "some assembly required" was disconcerting, considering the price for the kit would be $550 Canadian. Yeah I know I didn't pay for it, why be such a hard arse, cut the vendor some slack. The washers couldn't be installed at the factory for that price? I failed to do a good job of getting the washers aligned with the surfaces on my first attempts, so a few of the holders the washer don't sit well. I'm looking at the sandwich of PCB between the holders and thinking, crap that doesn't sit well. There were two spare washers provided. Maybe later I will revisit the wonky washer placement.
The unsettling feeling didn't end with the washer insulation. The holders secure a PCB by pinching the board between the plunger and head of the holder. The need for the insulated washer become evident at this point. Positioning the four holders around a PCB you create a platform, not unlike a oil rig with legs that extend down into the sea. The magnetized holders are the legs of the platform that adhere themselves to the metal base plate.
The picture contains an inset pictorial from the user's guide. It demonstrates using two oscilloscope probes.
The PCB platform reminded me of a Jenga tower, late in a game. Is it stable? Can I move this block? Will it come tumbling down? The four PCB holders must be strategically positioned around the PCB.
The faces that touch the PCB are insulated with the aid of the washer but the edges of the holder are not. I didn't feel confident that I could install the holders without shorting out the PCB. For that reason I used a first generation Pi I had kicking around. Notice the large SD card used in earlier versions. If I failed in positioning the holders, resulting in letting the smoke out of the PCB because of a short then my loss would be less. The PCB holder positioning exercise took some effort. Connectors on the board get in the way. Headers and overhang of components have to be addressed. Both sides of the PCB have to be examined to ensure the holders are not making contact with live parts of the PCB.
The PCB in the picture is intentionally installed with the top of the PCB facing the base plate. The user guide suggests the mirror surface of the base plate enables viewing of any indicator lights on the PCB. That worked. I could see the flashing lights of the Pi during boot up. Sounds like a good idea. I found it difficult to keep the mirror surface of the base plate free of finger prints and smudges. You will need to keep a bottle of glass cleaner around if the surface becomes tainted. Oh yeah, be sure to clean the surface before you start. It is difficult to move a Jenga tower during the game.
With a light positioned to take pictures, I was seeing white spots in my eyes after picking up reflections. I'm not sure how this would work in a area that had bright overhead lighting.
With the PCB platform suspended above the base plate on the four holders, I positioned the oscilloscope probe holders. One end of the probe holder is magnetized and contacts the base plate and the other end, that is weighted, holds a oscilloscope probe. Oh, not just any probe! The holders appear to be designed for Pico probes. Makes sense. The probes I had available did not have ends long enough to pass through the holder and still make contact with the PCB. In order to perform the test, I borrowed the Pico probes from the kit that was waiting to be returned to Pico.
The end of the Pico probe is designed to pass through the holder. In addition the probe pin tip is spring loaded. The weight of the probe holder applies pressure to the probe tip keeping it in place on the PCB. I noticed in the probe parts bag, extra pins for the tip of the oscilloscope probe. Someone was thinking ahead.
The oscilloscope probe cables are secured to the probe holder by cable holders. Two cable holders in a eight colours is provided. 16 rubber bands to keep in one place. The idea is to colour code the probes in order to track what input they are associated with on the oscilloscope. I like the idea but, I think the cable holders will get lost in the shuffle and wraps of coloured wire will adorn the cables to keep them in place. Well in my world they will.
I was surprised at how secure the probes were when positioned on the board. The power cable for the Pi was not long enough to reach the wall socket so I had to move the oil rig platform across the desk. After applying power, I discovered the Pi power cable blocked access to my computer keyboard. Once again the rig had to be moved, this time with power applied. I can say that no Pi's had their smoke released during this exercise.
The user's guide had a warning. The magnets supplied in this kit have strong magnetic fields. Users of pacemakers and insulin pumps must avoid using these items. Ok, that explains why the mounting is secure. Like most males I didn't read the instructions until later. Good thing I left my pacemaker and insulin pump in my other body.
The struggle to position oscilloscope probes on a PCB in order to free up your hands to perform other tasks is arduous to say the least. Couple that with the frustration of poor contact or probes coming away during measurement, I can see a strong desire to have a probe holder kit. I feel the intent of the Probe Positioning Kit is admirable. It does work provided you overcome some challenges.
My initial feeling is this is equipment is fluff. But wait, I have nothing else to do while waiting for the equipment. After some sober second thought, this is gear that can work in a lab environment lab but in my opinion, is not field suitable. Even in a lab, there will be some struggles maintaining an environment using the system so that it performs reliability. Getting those towers position to prevent a short on the PCB is the first critical step. Getting all the right probes to fit the holders, with their colour coded cable identifiers in place is next. If the environment can remain static, this is a great setup to take measurements. Lift a probe and move it to take another measurement, great. If the working environment is not static and does suffer pressures of being communal, you will have some challenges to get it working. Wearing a white lab coat while using the kit might be the required emphasis to make it work.
I do plan to use the kit later with the scope. I may try a probe test but I know it holds the PCB in place. Now am I confident enough it won't short out my Pi4b, I'm not sure.