LeCroy HVD3102 (Differential Probe) will work with TEK MDO3000? - Page 1
Forum section: electronics / testgear

author: onesixright
author_rank: Frequent Contributor
timestamp: July 28, 2016, 10:55:11 am
content: Hi All,Maybe a stupid question, forgive me.As stated in the subject, any change it will work (since it uses the ProBus)? I know LeCroy have a adapter to connect TEK probes to LeCroy, but i didn't find one for vice-versa.Thanks!

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: July 28, 2016, 11:43:54 am
content: I don't think there's an adapter to get a ProBus probe onto a Tek scope. LeCroy itself only has the TPA10 which as you know goes the other way around (Tek probe on LeCroy scope), and for it to work it also relies on support by the scope's software, so it's a bit more than just a piece of hardware.I very much doubt there's anything like that from Tek.

author: onesixright
author_rank: Frequent Contributor
timestamp: July 28, 2016, 01:02:07 pm
content: Thanks, i thought so

author: robert_
author_rank: Regular Contributor
timestamp: July 28, 2016, 01:29:04 pm
content: Some simple active probes would work given a +-12V supply, however the HVD31xx does use the I2C bus for control (range switching, offset) too. It might be possible to make something (problem being that ProBus isnt really documented, and TekVPI is even worse), but theres nothing that would work right out of the box.

author: MarkL
author_rank: Unknown
timestamp: July 28, 2016, 07:48:28 pm
content: Quote from: robert_ on July 28, 2016, 01:29:04 pmI have a similar problem as the OP but with a different probe.If no official documentation, has anyone done any reverse engineering on the ProBus protocol?

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: July 28, 2016, 08:13:24 pm
content: Quote from: MarkL on July 28, 2016, 07:48:28 pmProBus uses I2C so it shouldn't be too difficult to sniff it. The challenge is to find out how the probe is controlled, especially if you don't have a LeCroy scope. And even if you have managed to find out, you still have to make your Tek scope talk to the probe in the expected format.I'm not sure that is really a sensible way. You might be better off selling the LeCroy probe and buy the Tek equivalent which fits your scope.Or sell the Tek and get a LeCroy

author: MarkL
author_rank: Unknown
timestamp: July 28, 2016, 09:44:01 pm
content: It's aDS1855ADA1855A diff probe amplifier, so it's still operable without using the ProBus connection. Not quite as bad as the OP's situation.If the protocol was available, I could interrogate the settings to set the vertical scale appropriately via either SCPI or, hack up an old probe compensation box and put the right resistance on the ID ring.As it is now, it's an annoyance and a source of error that eventually results in "Oh, yeah..." moments. Buying an old, near-death LeCroy to figure out the I2C piece may still happen.I really hate these proprietary, lock-'em-in probe interfaces. They're all guilty of it.Edit: Typo in model number.

author: robert_
author_rank: Regular Contributor
timestamp: July 29, 2016, 12:57:38 am
content: First, have a good look at whats inside as it might be quite easy to figure out how it works. An AP015 current probe for example just uses a regular PCF8574 I2C port extender to control all of its innards, and an 24C02 for ID.Oh, the ProBus has an pin (upperright) that is connected to the BNC "ring" too, and many probes just use an resistor there to set attenuation. Same R values as for Tek and Agilent too. There also are "reserved" values that select wether it is an "intelligent" probe so the scope reads from I2C.With some luck, all it would take is to connect that pin to the BNC ring on your tek.At the moment, i am working on converting an Tek P5205 to ProBus (so the other way round), which does seem to be quite successful so far. The 5205 seems to run fine on +-12V (Tekprobe is +-15 but on the scopes i tested, it was more like +14 -14,5). I know i could buy an TPA10, just its way overpriced and i cant justify to pay 1k for something i can build for <5% of that price. Plus its interesting to see whats possible and what not, just as it is with all that software...If your probe were a HVD3106, i would happily swap that P5205and maybe even throw in that hugely overpriced TekVPI to Tekprobe adaptor.

author: MarkL
author_rank: Unknown
timestamp: July 29, 2016, 02:22:33 am
content: Quote from: robert_ on July 29, 2016, 12:57:38 amThat was worth a try - thanks! But unfortunately, there's no resistance on the upper left pin, or any of them for that matter, that changes when I change the attenuation on the probe amp. So, it must be communicating changes via I2C.I'm afraid it's going to take a LeCroy scope to figure this out by watching the I2C conversation.Does your 5205 change a pin resistance on the TP2 interface for 50x vs. 500x?

author: robert_
author_rank: Regular Contributor
timestamp: July 29, 2016, 08:20:11 am
content: Quote from: MarkL on July 29, 2016, 02:22:33 amYes, but only when its powered up.UPDATE: Its the upper right pin. I looked at the wrong layer in the PCB, too late in the evening...270Ohms sets some flavour of "smart" probe (that is used with all i have).If it uses i2c, i would not be too surprised to find a PCF8574 or similar in there to read back the attenuation setting, so open the probe/amplifier box before investing much time in analysing the bus communications.