Want to know if a Saleae original logic analyzer is sniffing your bus traffic? It's easily done in software using a single digital I/O pin! www.analogzoo.c... /
I checked my Hantek 4032L. It leaks a tiny bit at all times. I took measurements with a fluke 787 which has approx 11Meg input resistance. 10k load = leakage of ~13mv (1.3uA) 1Meg load = leakage of ~180mv (1.8uA) The Hantek has an input inpedance of ~215k (measured) 200k (spec).
just saw this topic. I would ask - Who uses a 1M pull up/down resistor anyway? A typical 1K to 10K probably wouldn't exhibit the same result so I wouldn't be too worried.
I wrote an open source firmware for the Saleae Logic (fx2lafw) as part of the sigrok project. As far as I know, it's not possible to do anything so smart - you're just seeing the natural behaviour of the digital input circuit.
+fractureforce Sure, I assume the Saleae configures an internal pull-up on its input pins, so the pins default to a logic high state - I'd agree that is natural behavior. Regardless of whether it is natural behavior or not though, it is still detectable (perhaps not practical in all situations, but detectable none-the-less). WRT the "natural behavior" though, it's actually a little stranger than what I showed in the video...there's a reason I was continuously pulsing the pin high instead of just waiting for the Saleae to naturally pull the pin to a high state. The Saelae actually asserts its probe pin(s) *low* until it sees a high input state; at that point, it asserts its probe pin high (again, presumably via a weak internal pull-up resistor). It will stay that way until the Saleae sees a low input state, at which point it will go back to asserting the probe pin low again. Maybe this is intentionally done in software?
FTDI has some kind of 32 bit FIFO to USB 3.0 converter. Wouldn't that be perfect for a high performance streaming logic analyzer? I haven't looked into it that much, but it looks like a FX2LP on steroids.
+Digger D I think that pretty much any logic analyzer can be detected in a similar manner, because I'd expect that they have to assert some default state on their inputs in order to prevent random noise from triggering a false rising/falling edge. What I found particularly interesting about the Saleae was: 1) It used a pull up resistor (other logic analyzers I've used have a pull down) 2) The pull up was disabled and the input went into a floating state when the probe saw a logic low state This is why, to detect it reliably, I had to pulse the pin state high. Otherwise, there is the possibility that the Saleae probe input will be in a floating state, and you would likely read a low state instead of the expected high state. For analyzers that have internal pull down resistors you could do the same thing, but make the external 1M ohm I used in the video a pull up rather than a pull down.
Easy dude, get this it is cheap ;D www.banggood.com/LHT00SU1-Virtual-Oscilloscope-Logic-Analyzer-I2C-SPI-CAN-Uart-p-988565.html and it got free software: sigrok.org/wiki/Downloads if you are an adventurer then maybe you wanna get this: sigrok.org/wiki/Noname_XL-LOGIC16-100M
Abhishek kumar Measure, record, and decode buses of logic voltage levels. For example, if you were having a problem with an LCD panel attached with a parallel bus, a logic analyzer could be used to debug glitches. Pretty useful tool especially if recording to a computer which will provide a huge history.
Example I wasn't sure if a sensor was getting my information. It was just annoying to write a piece of code to sniff the line. Hooked up the LA, BAM done. Now I had to figure out if all the information contained was what I needed.
