Notes Regarding the Ultra Probe Schematic.
Added 2023-09-16 19:20:26 +0000 UTCAwake for 18 hours and.......
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OK, I think I figured it out (but I would still be interested in your opinion and maybe Paul will also weigh in): we have a very high impedance input here, which is basically 40 Mega Ohms (the two 20M in series). So we really need a very high impedance protection device. I just measured an 1N4148 in reverse with 10V (much higher than the 0.6V we have here) with my Keithley 160 and found 2.8nA current. The BC547C however had an immeasurable current of less than 100pA. So the transistor has a higher resistance in reverse. However, with 3.5GigaOhms the reverse resistance of the diode is still much higher than the 40MegaOhm input resistance we have here. So this should not make a real difference. Next I measured in forward direction. I took 270mV as voltage, as this seemed like a reasonable voltage we might encounter (probably even much less). The diode had a current of 487nA giving a resistance of only 554 kiloOhms. The transistor had a current of 0.8nA, resulting in 337 MegaOhm resistance. What a difference! While the resistance of the transistor is much bigger than our input impedance, the diode would already weigh down the input to 500 kOhms! Unacceptable! So this is a clear reason why we need to use the transistor circuit instead of a simple diode! I also tried with 64.2mV (pretty much the smallest voltage my power supply can deliver) and I still got 5.4nA current for the diode, which is equivalent to 11.8MegaOhms resistance (still much less than the 40MegaOhms we are aiming for, so unacceptable), while I could not measure any current (so less than 100pA!) for the transistor, which results in at least 642 MegaOhms (probably much more, but I can't measure it) -- plenty for our case! So this is convincing, it is all about the forward resistance for small voltages!
Helmut Heller
2024-10-12 09:54:25 +0000 UTCHi Paul! A bit late to ask, but I am just now turning to your ultra probe. Can you explain why you used the two transistors Q1 and Q2 to protect the FET and not just two simple diodes, 1N4148, to GND and Vcc? What is the reason? Lowering the input capacitance (load)? Or do diodes leak too much? Thanks, Helmut
Helmut Heller
2024-09-30 17:01:02 +0000 UTCI have a frequency counter which likes TTL input levels. I have several times thought of building a probe which might allow me to count lower level signals at frequencies up to 100 MHz. It occurred to me this probe would make a good no-contact way to do it. I see it is very sensitive and I can control amplitude by proximity. I can get amplitude to TTL level. So it seems ideal if BW is enough. Did you have a goal in mind? I realize you haven't characterized it yet.
Joseph P. Miller
2023-12-01 22:22:47 +0000 UTCThey are both fine. If you are going to build your own variation of my PCB design, use the schematic. If you copy my design exactly, use the PCB.
Mr Carlson's Lab
2023-10-05 21:11:03 +0000 UTCOkay - so the PCB is golden - not the schematic. I'll build as the PCB is laid out. Thank you, Paul.
Donald J Arndt
2023-10-05 21:06:08 +0000 UTCExplained in this video, (1M resistor) and see the notes on the schematic, (Updated about 2+ weeks ago.) The prototype design went through about 15 changes before publishing, and the way you see it is the last design. The one you see now is one of the various changes (In short, the differences don't matter.)
Mr Carlson's Lab
2023-10-05 20:59:01 +0000 UTCOkay, will do. Thank you. What about VCC going to both 1M and 1.2 K resistors on the PCB (near Q1) but not on the schematic?
Donald J Arndt
2023-10-05 20:36:56 +0000 UTCWatch the video's carefully, it's explained.
Mr Carlson's Lab
2023-10-05 20:25:23 +0000 UTCHi Paul - I am a bit confused where you have the Negative power wire coming out the back end of the PCB. It looks soldered to the junction of the two 10k resistors in the gain section not to the negative rail at the bottom of the PCB - there is no wired connection to the - (minus) GND where there is also a drill hole.
Donald J Arndt
2023-10-05 00:24:03 +0000 UTCCan this be used as a shorts finder like the eds Leakseeker 89?
nosaj seveer
2023-10-01 03:40:39 +0000 UTCPleas - take some rest and some tea
Andrew Koala
2023-09-28 12:44:50 +0000 UTCyou are conducting the Music :
matthew levin
2023-09-28 00:14:34 +0000 UTCMr C. Can you please post a parts list for the Ultra probe that shows standard semiconductors (not SMDs) ? Much Thanks.
Steve Rys
2023-09-25 15:33:11 +0000 UTCThanks for the clarification, Paul
Brian Wood
2023-09-24 11:36:18 +0000 UTCPaul thank you for all you do. I absolutely look forward to each and every new post!
Jason Bryant
2023-09-24 00:40:15 +0000 UTCI just had a similar experience recently where I sent a machine shop some mechanical drawings for quoting, and it came back wrong. After a couple of iterations, I discovered I had a couple incorrect drawing references on one. So, I had to eat CROW. I hate when that happens!:-~
Ozy
2023-09-22 06:09:22 +0000 UTCHi, please quickly flick through the 70 posts (so far) written by people and some (including myself) had offered links below the main ultra probe video. Please note, that there is more than 1 manufacturer that make the very same pump . Solomon is simply just one of them and it just so happen that MCL has found it first and he recommended it to us. Here are some examples: Solomon SH-817A found @ tme.eu Weller 7874B found @ Amazon.com Solomon SH-817B found @ stewmac.com and yes, all of the above come with metal caps and the threaded brass piece inside (behind the tip cap) according with that people have commented. I hope it helps.
Ovi4
2023-09-20 15:56:55 +0000 UTCHi All... anyone know where I can get the Solomon SH817B Solder Pump to purchase?
Andre Gopee
2023-09-20 15:12:32 +0000 UTCAli express practice kits are good brother. It's what I use but I should've broke all the boards and fixed the traces because I was fixing a ps5 all day wirh torn traces
Joey Strong
2023-09-20 00:53:08 +0000 UTCI got my bottle of liquid tin on the way and a broken tek scope my buddy has 2 of. He never got around to fixing them but now he's too busy
Joey Strong
2023-09-20 00:51:15 +0000 UTCWatched your video on mounting surface components. Very helpful. No longer afraid of them. Thanks for all your videos.
Steve Spence
2023-09-19 18:47:42 +0000 UTCAll - I have ordered the parts and all were found easily at DigiKey. Now I need a PCB - any chance I could get one from any of you? Willing to pay. Thank you. DJA
Donald J Arndt
2023-09-19 18:02:00 +0000 UTCWhat is the overall gain of the circuit with the gain switch in both positions?
Tony Contrada
2023-09-19 15:43:14 +0000 UTCBy the gain switch (pad) there are two 10uF ceramic capacitors (one to the left and one to the right) but both connect to the ground via a common trace that leads to ground (GND) with the help of a so called ,,thru pad,, or ,,via... PS: Just in case you don't know what a ,,thru pad,, is. It's a pad that has a drilled hole thru it and it communicates to both sides of the PCB. the bottom side of the PCB (in this case) will act as ground plane. That means is that any thru pad (from the current design) will be electrically connected to it and so will the two caps described above. Again, a thru pad is easy to spot since it has the word GND written next to it
Ovi4
2023-09-17 15:31:59 +0000 UTCIt appears to me than the capacitor by the gain switch goes to the positive rail on the circuit board but is shown going to ground on the schematic. Is this capacitor attached to the positive rail ? I'm referring to the 0.1uf cap located below the power rail above a 10k and next to the via on one side and a 10uf on the other.
Ken Fay
2023-09-17 14:41:18 +0000 UTCPlease watch the short video addon called '' Notes Regarding the Ultra Probe Schematic'' that MCL posted here (above) 17 hours ago and you'll understand about the discrepancy.
Ovi4
2023-09-17 12:16:24 +0000 UTCHi Paul. As Antti Louko did before me, while analyzing the layout of the board I have spotted a discrepancy with the schematics. Specifically, the 1 Meg resistor at Q1 is tied to VCC on the board while between base and collector on the schematics. I guess the board still works nonetheless...
Philippe Penochet
2023-09-17 11:28:05 +0000 UTCI knew! Thanks for the correction :) And get some sleep, Paul - you clearly deserve it!
Keri Szafir
2023-09-17 07:53:08 +0000 UTCThanks for the update Paul. Your dedication is extraordinary. Just be sure to catch up on your sleep, even though we know it is overrated. :o)
Merritt Derr
2023-09-17 00:20:20 +0000 UTCI'm going to bed… some count sheep, I simulate circuits in my head
Thomas Eriksen
2023-09-16 22:43:13 +0000 UTCThank you, Paul. You are making our lives a tad bit easier :) Thank you for the work and generosity you are putting in!
Rex Hamilton
2023-09-16 22:15:22 +0000 UTCJust be sure you don't put the resistors in with the wrong legs to the left! I need some more sleep too. 😜
Chris Bennett
2023-09-16 21:55:25 +0000 UTCThanks Paul - this is lining up nicely for my next project - spent this afternoon making the board for my Forecasting Capacitor Tester build :)
Andrew Cockburn
2023-09-16 20:25:28 +0000 UTCThank you Mr C! You just simply know more than I ever will !! I love your projects, keep them coming !!
Bob Sheldon Sr - KC9ITB
2023-09-16 20:18:23 +0000 UTCThank you.
Alan Wood
2023-09-16 20:05:00 +0000 UTCThanks, Paul. Charlie said to get some sleep! LOL
Robert Calk Jr.
2023-09-16 19:46:14 +0000 UTCgood catch. I don't know enough to catch that...Yet!
James Roberts
2023-09-16 19:42:41 +0000 UTCThank you for all your hard work Paul!!!!
Michael, KE4EST
2023-09-16 19:30:04 +0000 UTCOnly 18? I'm currently up since 0700 Friday... 30+ (Swing shift swap over weekend.) I'm planning on doing a probe build as my 4Q2023 project. Haven't added anything homebrew to the bench gear lineup in a year or two.
FunkEngine
2023-09-16 19:28:03 +0000 UTC
