This is a short review of the SensePeek PCBite kit, 4019. When I was reading the recent roadtest reviews of the PicoScope 6424E, the PCB and probe holder kit that came with it looked really useful. These are actually a rebranded version of the SensePeek kit, elements of which can be bought separately. I acquired the kit, model 4019:
The kit comes with all the above (not shown are 2xspare probe pins and a cleaning cloth)
Base Plate
This is a double sided, A4 sized metal base plate. One side is matt and one shiny, ostensibly so that the underside of a PCB can be viewed through reflection. The kit comes with an an insulating cover which can be permanently attached to one side - in these pictures I have attached it to the matt side:
| {gallery} Base Plate |
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Large base plate with insulation cover attached |
Large base plate, reflective side. It's very reflective!g |
The kit comes with a microfibre cloth to keep the reflective side clean; given it's prone to capturing fingerprints that's very useful.
Being metal, the magnetic PCB holders can be placed on top to securely position a PCB.
PCB Holders
The kit has 4 PCB holders machined from aluminium. Each requires 2 insulating washers to be fitted, which can be a bit fiddly and I can image that anyone with fat fingers will struggle a little to position them. The posts are spring-loaded: pull the top shaft down, insert the PCB edge and let go. The springs are strong and there is no danger of the PCB being accidentally released. The insulating washers are required as the holder grabs into 4mm from the edge if inserted fully.
| {gallery} PCB Holders |
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PCB Holders: Four, in black anodised milled aluminium. Really nice. |
PCB Holder: Pull back on the spring-loaded shaft to open the holder. Maximum thickness of the board is 6mm. The spring is strong and will grab the board firmly and securely. |
PCB Holder: Grabbing the board. The base of each holder is magnetic and sticks firmly to the base plate. However, the posts are very smooth on the bottom and can easily be slid around the plate to reposition the PCB without removing first. |
PCB Holder: This grabs on to approximately 4mm of the board. You will need to find a suitable position clear of components - you could see that the test points towards the top of the image would prevent that part of the board being used. I think grip would be compromised somewhat if the board wasn't fully inserted into the holder. |
Probe Holder
The kit comes with 4 probe holders, approximately 355mm long.
At one end is a magnetic foot which works as well as the PCB holders - i.e. it grabs well and is smooth enough to slide around. At the other end is a M4 thread which is used to attach a probe head - either a SP10, SP100 or SP200 probe. The actual lead is very flexible and floppy - it has no resistive strengthener in it which means that it provides no resistance to probe positioning so won't twist or pull-away the probe head once it is positioned on the board.
SP10 Probes
These are x1 probes and the kit comes with 4 of them, with 4 replacement points, 1 set of banana plug connectors and 5 logic connectors (actually, just dupont leads.)
The probe heads are designed to screw onto the end of the probe holder.
| {gallery} SP10 Probe |
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SP10: The probe tip is a very sharp, standard pogo pin (spear point, 30degrees) and 1 spare is provided - the existing pin can be pulled out with fingers or pliers (no doubt lakes of blood will ensue if you try your fingers!) The dupont leads connect to the pins which are both connected to the probe pin. The probe head screws onto the probe holder with the silver body. |
SP10: Other side. |
SP10: Attached to the banana plugs and the probe holder. I've attached both leads to the pins but this wouldn't work in practice - the black lead should be connected to the ground of the DUT. Alternatively two instruments could be connected to the probe head. |
SP10 on Board: The probe head is positioned where needed, here on a SOIC IC. Despite its flexibility and lack of resistance, the probe holder easily holds the probe in place with no difficulty. It's own weight prevents it slipping or pulling away. |
SP10 on Pin: Here's a close up of the probe on one of the SOIC pins. The spring action of the pogo pin and weight of the holder keeps it in place. |
Two SP10s on Pins: The probes are held stably enough that two can easily be placed next to each other on pins. |
These probes are only suitable for measurements below 10MHz although with a logic analyser they will allow for decoding up to 25MHz. I measured the resistance of the pin to either connector as 0.08ohms. Whilst there is a replacement pin I wouldn't be surprised if it gets lost! These appear to be standard 0.5mm diameter, 30 degree spear tips, similar to these Product LinkProduct Link (actually, this one is a 45degree point); basically, P-50-B-xxxx pins which are 16mm long and 0.5mm point and 0.68mm shaft. From what I can find, they are readily available from lots of places.
SP200 Probes
These are 200MHz, fixed x10 probes; SensePeek also sell SP100 probes which are 100MHz equivalents.
| {gallery} SP200 Probe |
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SP200: Kit contents. The probe head (with spare pin, not shown); an adjustment screwdriver; two different length dupont connectors for the mini-grabber which are used for a ground connection; cable ties of different colours; a probe holder as described earlier; and a cable with BNC connector at one end and a push-fit plug at the other end. The probe head has the dupont male connector and probe lead push-fit socket just behind the ground-connected shield. Note that there are also two pads on the head to which an alternative ground connector could be soldered (carefully.) I assume that's to provide a smaller ground loop for measurements - I think one concern with these probes is the inductive ground loop caused by the leads and mini-grabber and I would have thought SensePeek would have provided an alternative ground connector. |
SP200: probe connected up. The probe head screws into the probe holder as described above; the scope lead plugs into the brass socket. |
SP200: As before, the holder keeps the probe very steady when attached to the board. The ties keep the cables tidy with colour identification. |
SP200: As with the SP10 Probes, the sharp point makes a good connection to pins and is steady under its own weight. The ground connection needs to be connected through the mini-grabber to a suitable point. |
Alternate Probe: It's possible to use a different probe with the holder. I found the positioning more difficult, possibly because the probe holder weight tends to drag and the blunt point of the probe doesn't 'stick'. I did find that keeping a shallow angle to the board helped. It does show how well the SP200 probe head with holder works though. |
The SP200 has an input capacitance of 14-18pF with an adjustment range of 15-45pF. They are rated for +/-60V DC and 30V AC RMS with a pk-pk of +/-42.4V max. Rise time is a calculated 1.75ns. Compare to my Siglent PP510 (100MHz) probes: 18.5 - 22.5pF input capacitance with an adjustment range of 10-35pF; 300V RMS; and a rise time of 3.5ns.
Performance
This is just some quick tests and not really definitive.
| {gallery} Basic DC test |
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5V DC Measurement: I have an SP200 on Channel 2 and a Siglent PP510 on Channel 4 measuring the same point on the circuit. As you can see, nothing to report and they both read pretty much the same except for one glitch reading. I did |
SP10: Taking a measurement at the same circuit point as the SP200 - the only way I could connect this probe was with a BNC-Banana plug connector with the probe connected to +ve and a separate lead to -ve. Here it is clear that the inability to tie a ground at the probe really affects readings, even at DC: this is a zoomed in capture of the 5V measurement and ringing is evident. In fairness to SensePeek they market these probes for DMM measurement with one probe connected to +ve and one probe connected to -Ve. My experiment was a bit of a lost cause really. However, I think this does point to a bit of a gap in their probe line. |
Taking a DMM Measurement - 1: Here, two SP10 probes are measuring across a capacitor with leads to the Keithley DMM in the background |
Taking a DMM Measurement - 2: Which gives a good reading. |
I also, for what it was worth, made a noise measurement with the SP200 and PP510 and again, there was nothing to report in terms of differences between measurements. Somehow I seemed to have lost the image I captured but it wouldn't have told us anything.
In the following images, I'm checking how well the SP200 can resolve a square wave across various frequencies. Channel 2, purple, is the SP200 and Channel 4, green, is the Siglent PP510
| {gallery} Square Wave Measurement |
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50MHz: My AWG isn't great at this frequency. However the signals are very similar; if you use your imagination the SP200 is slightly flatter at the peaks and troughs. |
20MHz: Here we're getting at least a recognisable square wave out of the AWG. Again the SP200 is better |
100kHz: Definitely square, with over- and undershoot on both probes. |
50kHz: No improvement so lets look at those over- and undershoots |
50kHz Overshoot: the SP200 resolves the waveform somewhat better than the PP510. The rise time is affected by the scope's capabilities. |
50kHz Undershoot: Again, the SP200 is better than the PP510 |
Summary
When I saw the probe holders in the Picoscope roadtest I thought they looked useful and having used them for a short time I conclude that they are. The probe holders themselves are definitely better with SensePeek's own probes but they can hold other probes with a bit of careful positioning. They hold the probes in place very well and don't pull or drag on them at all. The magnets are strong enough to hold the probes in position but can easily be slid to alternate positions without disturbing the probe on the board; ditto the PCB holders.
The PCB Holders can be used in other scenarios as well, for example soldering. I'm not sure how well they would hold up to hot air pencils mind given the insulating washers.
The probes I have mixed feelings about. Although they look Heath Robinson, the SP200 are fine for their price and certainly no worse than the ones I have with my scope. The sharp points are great for close pin positioning and measurements which can't be safely achieved with the wide, blunt standard probe tip. The SP10 again are fine if used in the right way - with a DMM, logic analyser (I didn't test this) or similar. They are of no use for taking measurements with a scope, even using two and the Maths function. The SP200 ground leads are too long for taking sensitive measurements and there's no provided alternative like the pig tail that comes with typical scope probes. It ought to be possible to jury rig something up: there's a big ground shield on the probe head as well as two bare pads. Soldering on another pogo pin receptacle - an R50-B-xxx- should allow a temporary ground pin attachment but I suspect the lack of flex may make positioning difficult. It's a solution cying out for a flexible attachment for a pogo pin - perhaps a short length of stranded wire.
EDIT: I forgot to mention initially the probe compensation. As with all x10 probes, they need compensating - with the SP200 probes it feels unnecessarily difficult. For a start given the style of the probe, it's hard to connect them to the scope's compensation point. But the biggest problem is with the compensation screw itself: you'd expect it to be a philips or slotted screw head, but it isn't, it's actually shaped like an arrow head - a tiny slot with a triangle. Or image a philips head where one of the slots has been ripped into a triangle with the adjacent slots. It's deep in the head so impossible to see what you are doing and there's no positive contact to feel for with the provided screwdriver. In short, it's a real PITA so it's fortunate it doesn't need doing very often. It took me ages to get it properly compensated.
I think SensePeek have missed a trick with their probes. Perhaps a x1 scope probe will come along and maybe some shorter ground connection and the compensation is ridiculous. However, in both cases the sharp points make them a useful addition to a test kit. As indeed I conclude the PCB and Probe Holders.
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