Products > Test Equipment
RPL1116 (MSO1000Z) and PLA2216 (MSO5000) Active Logic Probe teardown
dren.dk:
Don't worry about the LED brightness I'm very annoyed by overly bright LEDs myself.
The LEDs used are these ones: https://datasheet.lcsc.com/szlcsc/Lite-On-LTST-C193TGKT-5A_C12065.pdf
From the datasheet we get a forward voltage of about 2.5-3.1 V, so let's call that 2.8 V and a max current of 20 mA.
The supply to the MCU is the -2.3/2.5 V rails, so that's 4.8 V in total.
I designed with 2x 220 Ohm resistors for a peak current of (4.8V-2.8V) / 440 Ohm = 4.5 mA.
I'm running the LEDs with a fixed rate charlieplex where each LED gets one out of ten PWM periods, so that means that the average current at 100% PWM is 0.45 mA per LED.
As I'm not a fan of bright LEDs I've turned down the PWM to 1/255, which yields an average current of 2 uA
The initial result was too bright, so I upped the resistors to 2x500 Ohm for a peak current of 2 mA and that seems about the right brightness.
I must say I'm very surprised about how much light is yielded by the charlieplexed LEDs even at a crazy low peak current.
We assembled serial number 3 last night, here's the recipient of #3 stuffing 0402 10 nF decoupling caps and swearing a lot.
#3 ended up working perfectly.
The recipient of #2 is in the process of printing cases for us.
The firmware for the voltmeter is also working perfectly, so after calibration the exact threshold voltage is reflected by the LEDs.
Sprite_tm:
As a warning for other people that try to DIY this using an LMH7324: there are fakes of this chip on the Chinese market, as I can unfortunately tell you from experience... I built my pod, and 8 of the 16 channels refused to do anything. Luckily, I own an advanced device for looking inside of chip packages to debug this issue... Seems they forgot to put the actual silicon into half my chips, grmbl. FYI, these come from Taobao; that was the easiest source I could get them from seeing as I live in mainland China.
Images (click to embiggen):
pmnxis:
I ordered PCB and parts with following this thread.
Thanks. I will try to assembly and test on my new mso5000.
in my case I spent 150usd more for parts and pcb. but it's interesting and cheaper than pla2216.
BTW I changed some connector and cable assembly for rapid works (there's no stock for connector, so changed little bit)
And I don't have experience about making IDC 1.27 cable by hand. so ordered already made one.
thmjpr:
Started on the USB C probe idea from Muza giving 4 signals per probe pod, 4 pods total. Schematic is basically straight copy of dren.dk then the connectors were changed out.
Main connector: https://www.digikey.ca/product-detail/en/sullins-connector-solutions/SFH11-PBPC-D25-ST-BK/S9201-ND/1990094 $3
Type C connectors: https://lcsc.com/product-detail/USB-Connectors_Jing-Extension-of-the-Electronic-Co-LCSC-USB-3-1-C-TYPE-DIP-SMTFemale-10-0L-High-temperature_C168698.html $0.50
Board is 1.6mm, ideally would be 2mm to match the header connector pin spacing but JLC just has their cheap impedance controlled board in 1.6 (JLC7628).
In retrospect, HDMI is a much better solution in almost all aspects: you don't have the polarity issue, and proper spec cables are easier to find. Probably why we've seen HDMI on siglent scopes and on CC payment terminals, etc. But, once you realize the quirks of USB-C its not too bad, its just that there are sooo many of them. Most cables wouldn't work, flipping the cable will of course screw up your channels (if you want to be lazy you can simply mark the "up" end on your cables), and active cables won't pass through our signal or could blow from the voltages we are using.
For finding the right USB cable, what you want is a passive "super high speed" or "USB 3.1 gen 2" or "10Gbps". These, if correct, indicate that all four high speed pairs are wired inside the cable. I bought two cables and it looks like they both are suitable (very surprising given how cheap they were, about 19 wires! need to be run and cables are hand assembled for the most part). They have the labeling: "VW-1 type 2725", unsure what it refers to (related).
Cable 1: https://www.aliexpress.com/item/30cm-USB-C-USB-3-1-Type-C-Male-Connector-to-Male-Data-Cable-for-Tablet/32825241462.html $3
Cable 2: https://www.aliexpress.com/item/USB-Type-C-Cable-USB-3-1-Gen2-USB-C-Male-to-Male-Data-Sync-and/32893896190.html $6
First cable is way too short (30cm), I bought it thinking it would be fake/mislabeled, but its not, has all the right pins wired up.
Second cable appears to be very high quality, again same internal wiring. Of course I can't tell the power cable diameter inside or bandwidth of the HS pairs, so quality is purely based on physical feel.
Neither of these cables seem to have the internal 1k pull-down resistor on CC2 line, which I was expecting. Also, all multi-pin connections VBUS/Gnd/etc. are connected internally on the cables. Knowing these two things would have made layout a bit simpler. Shield is internally connected to Gnd as well, no messing around with having that connected in some strange way.
For the CC2 line, basically there are two polarity detection lines, CC1 and CC2. One is connected through the cable and one is not. So based on where that pin ends up, you can determine which one of the four orientations the cable is in.
gizmo5418:
Hi,
I want to thank you for this great LA project. I successfully made LA to MSO5000. All channels work, but channels 1, 3, 5, 7, 9, 13, 14, 15 have a negated level, as in the screenshot of the MSO5000. Voltages -2.5V, + 2.5V, + 4V, Vref1, Vref2 are correct. I noticed the same negation of channels in the user's picture dren.dk.
It seems to me that the signals of negated channels in the LA project are reversed - one should introduce a correction on the PCB Breakout..
I am sorry for my English, I use a Google translator.
Regards,
Pawel
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