Logic Analyser Pods

[ThermalRunaway]

Hi everyone. I've managed to aquire a Thurlby logic analyser, but unfortunately it has no data pods. I've never fiddled around with data pods before, what's generally involved with them? Are they simply probe connections to the front panel of the analyser, or is it more sophisticated than that?

The reason I ask is that I can't seem to find anyone who would sell data pods for the analyser I've aquired, but if the pods are simply acting as connections to the front panel of the unit it would be relatively easy for me to make my own, provided of course that I knew the pinouts of the connectors on the front of the analyser. If the pods do much more than just connect the outside world to the analyser then of course I'll be stuffed on that idea.

Thanks for any advice,

Brian Hoskins

 

[ThermalRunaway]

I've just sent a message off to TTI via their website. Maybe they still sell the data pods for it. I'd be interested to get it working because I've needed an analyser loads of times. I used to have a really nice one which used my PC as the interface, but it got stolen along with all the rest of my test equipment when I was burgled last year. Hmph.

Brian

 

[hjames]

Geez, the thieves in your neck of the woods are definitely a different breed... logic analyzers...

On my Agilent MSO, there are 16 signals that plug into something that looks suspiciously like a 40 pin header. Personally I expect to see some sort of attenuation network or something inside, but I've never bothered to pop the thing open. I might post something in another 24 hours or so (it's at work), if I don't forget about it.

James

 

[ThermalRunaway]

The thieves actually cleaned my house out completely. The sad thing is that they probably threw most of my test equipment away, thinking it was of no value or too difficult to move on. The truth is they made off with thousands and thousands of pounds worth!

Thanks for the reply. Brian.

 

[Nigel Goodwin]

The thieves actually cleaned my house out completely. The sad thing is that they probably threw most of my test equipment away, thinking it was of no value or too difficult to move on. The truth is they made off with thousands and thousands of pounds worth!

A friends of mines son is at Newcastle Uni, and he shares a house with two or three other lads - so usually there's always someone there. But one night it was one of their birthdays, so they all went out for a drink - only gone about two hours!.

When they got back the house was completely emptied, all furniture, all possessions, even carpets, all their uni work - just a bare shell left.

Presumably someone knew this was the only night they were all out?.

Their landlord was really helpful, he provided them furniture (and beds etc.) while they waited for the insurance to pay out - which they eventually did!, and they then paid him for them.

 

[hjames]

Ah, no good - The thing looks like it's been riveted together or something. There's nothing in the service manuals about the pods either.

On the other hand, when I measure the resistance of the little detachable probes, I see a 90.4K resistance. It looks like the pod itself is just part of the wiring harness. (I see 90.4K measuring between the probe tip and the main connector when I plug the probe back in)

 

[ThermalRunaway]

Hmmm. I'd expect to see less than 90K if the pods were acting merely as a wiring harness. TTi didn't have any data pods for my model either, so I'm drawing blanks so far. There can't be much to the pods though surely - maybe there's some simple signal conditioning going on so that the data signal is buffered and then presented to the analyser in the correct format (TTL or whatever). At first I dismissed that idea, thinking that any signal conditioning would be more easily done from inside the analyser itself, but I suppose it wouldn't be cost effective to design an analyser like that would it. My analyser has 80-odd channels, but not everyone would use the full 80 channels all the time - so it would be more cost effective to the customer if they only had to purchase enough buffers/signal conditioners to satisfy their requirements, rather than having the full compliment built into the analyser. So yeah that's possible. Maybe I could just stimulate a couple of the pins with an oscillating 5V square wave and see if it captures them.

Anyone else know what the function of the data pods is on a Logic Analyser?

Brian

 

[hjames]

Lemme describe that again - there's a 90K resistor sitting right at the probe in order to decrease loading (since inserting a couple dozen/hundred pf from cables tends to be bad from an instrumentation perspective). This resistor is ~1" from the actual signal. Everything behind that is either a wire, or there might be some inductance/capacitance network in order to compensate everything properly.

I'd expect that if I tried to measure the input impedance of the logic analyzer, I'd see a 10K impedance looking into it. Actually, one of the specs of this analyzer is a 100K input impedance for the logic inputs.

Considering that the logic thresholds are usually adjustable, I'd expect to see a bank of comparators right behind some buffer. I'd expect all 80 channels are fully populated - the analog stuff is probably only a couple percent of the full hardware cost. I'd guess that the custom interface chip and the fast memory behind it is where most of the expense is.

James

 

[ThermalRunaway]

Yes I see your point on that. Ok well I'll do some digging around and see if I can get some pinout information on the connectors at the front. If I can find something, I'll see if I can stimulate a few pins with a clock signal and try to capture it on the analyser.

Thanks for the replies.

Brian