Red pitaya:open instrument

[grimmjaw]

Hi guys,

What do think this project, it claim that it can do Osiclloscopes, logic analyzers, spectrum analyzers, signal generators for  299€.
The project seem to be well designed (gantt diagramm etc ) but replacing traditional instrument seem to be 

http://www.kickstarter.com/projects/652945597/red-pitaya-open-instruments-for-everyone

I'm not connected with this project in any way (not a contributer) . i know you guy loves pocket DSO

[madires]

2ch analog output with 125MS/s isn't a 125MHz 2ch arbitary waveform generator. I would assume that the red pitaya team knows that.

[free_electron]

hmmm. here is my concern.  this thing ill acquire data , crunch it and display it as a web page , that is then transmitted wirelessly to a client....

what's the screen refresh rate going to be ? one image every 5 seconds ? one image a second ? it'll be as good as useless.. good luck trapping a glitch with that scope , or a spurious signal with that spectrum analyzer...

[Amarbir[Lynx-India]]

Very interesting if they make it i will buy it

[edavid]

Does it have PGAs and trigger hardware?  Without those, it's not going to be much of an oscilloscope.

[komet]

"Rudimentary, Elementary Design: Pain In The Arse? Yes, Always."

[free_electron]

"Rudimentary, Elementary Design: Pain In The Arse? Yes, Always."

That may indeed sum it up.

I'd have to see it for myself , but my initial worries (may be wrong). Is screen refresh and the fact you need another piece of hardware to visualize.

Imagine a scope where, if you hold the probe to a signal you het an update every few seconds.

Of course it is open source and all , but that incurs another question. Of the people buying it , how many will be really proficient enough at linix and xilinx , vhdl to actually make meaninfull additions to it ? Just because a million people have the source that doesn't mean anything ... 

Look one million people have a ferrari in parts... If they just knew how to put it together (a few may be able to do that) and have  a drivers licence ... But first i'll need to get a job to get money for fuel ... And in the country i live, roads havent been invented yet ... You know, along those lines...

Of course i applaud the effort. As for practicality and usability... Dunno. Maybe with some more spit and polish.

There was another comment. Why on earth sma. My thoughts also. Sma is a comnector designed to be mated once in its life (using a torque wrench) and be left alone. If they had put on 3.5 mm connectors... ( no they are not the same ! 3.5 is designed for frequent mating. ) and, at the frequencies they are mucking with, BNC would have been perfectly fine.

Also, the strange angles of the comnectors will make a housing for this thing a pain... If im going to use this a stest equipment i dont want to have a bare board on my bench. The bench is full of pieces of solder ,spent  solderwick, snipped off component pins, stubs of wire.  Box please ! Any test equipment has a case. Sure it looks 'cool' , but test equipment needs to be robust .

[ElectroIrradiator]

There was another comment. Why on earth sma. My thoughts also. Sma is a comnector designed to be mated once in its life (using a torque wrench) and be left alone. If they had put on 3.5 mm connectors... ( no they are not the same ! 3.5 is designed for frequent mating. ) and, at the frequencies they are mucking with, BNC would have been perfectly fine.

I'm speculating component availability, combined with the need for board edge mounting. Board edge mount BNC connectors do exist (so Amphenol claims, at least), but I couldn't immediately find them for sale anywhere available to me, last time I checked. Same thing with the other, more uncommon RF connector choices. Thus SMA...

[Amarbir[Lynx-India]]

Also, the strange angles of the comnectors will make a housing for this thing a pain... If im going to use this a stest equipment i dont want to have a bare board on my bench. The bench is full of pieces of solder ,spent  solderwick, snipped off component pins, stubs of wire.  Box please ! Any test equipment has a case. Sure it looks 'cool' , but test equipment needs to be robust .

Boss ,
     The End Product Surely Should Have a Enclosure .If Not Its Not For Mortals Like Me And You We Have Dirty Tables And Workshop 

[free_electron]

There was another comment. Why on earth sma. My thoughts also. Sma is a comnector designed to be mated once in its life (using a torque wrench) and be left alone. If they had put on 3.5 mm connectors... ( no they are not the same ! 3.5 is designed for frequent mating. ) and, at the frequencies they are mucking with, BNC would have been perfectly fine.

I'm speculating component availability, combined with the need for board edge mounting. Board edge mount BNC connectors do exist (so Amphenol claims, at least), but I couldn't immediately find them for sale anywhere available to me, last time I checked. Same thing with the other, more uncommon RF connector choices. Thus SMA...

But why board edge ? that thing doesnt go above 60Mhz ! no need for edge launch connectors. Come back with your edge launch when you muck around in the GHz domain.  Edge launch is just a 'coolness' factor in this design. A Trabant with a spoiler does not go faster , it just costs more (e dge launched sma is more expensive than a standard right angled BNC as well !

[alm]

They discuss the SMA issue on the KS comments page. They claim that it was just about the size.

I agree that standard right-angle BNC connectors would have been the best solution, although that would have required a different PCB form factor. If only because BNC is the standard for low frequency test interconnects. Good luck finding an SMA scope probe that is not designed for GHz applications, for example. I don't think SMA is that bad though. SMA is used in plenty of applications where the number of mating cycles is more than 1. Some sampling scopes, for example. Usually you would use connector savers to limit the number of mating cycles. Amphenol specs these SMA connectors for 500 mating cycles in stainless steel or 100 in brass. This is with a proper torque wrench, of course. A connector that is designed to be mated once in its life is called a crimp or solder connection.

And what will happen after you reach the maximum number of mating cycles or use an incorrect torque? The impedance match will become worse, VSWR will go up and bandwidth will go down. So the SMA connector may be only good for 200 MHz instead of 20 GHz. Who cares for a 60 MHz device?

I found it odd that the KS page is very light on specs. I assume that the inputs are 50 Ohms with a fixed attenuation, making it kind of useless as a scope unless you connect an active or low-Z probe with various attenuators.

[ElectroIrradiator]

But why board edge ? that thing doesnt go above 60Mhz ! no need for edge launch connectors. Come back with your edge launch when you muck around in the GHz domain.  Edge launch is just a 'coolness' factor in this design. A Trabant with a spoiler does not go faster , it just costs more (e dge launched sma is more expensive than a standard right angled BNC as well !

Didn't say I agree with their decision to go with board edge connectors. Probably more a case of them having some idea for the size and cost of the widget, and without a housing they needed to mount the input connectors directly to the board somehow. Additionally this solution looks 'cool' as you say, at least until you start to think about actually using it.

Board mounted SMA connectors, either edge or right angle, are actually a neat solution for many RF connectivity problems, even though they must be considered way overkill for what they are sometimes used for. Recently I considered using an edge mount SMA connector in a little RF project (hasn't been built yet), even though it is a small piece of test equipment. The trick here though, was the BNC at the other end of the cable making the SMA connection semi-permanent.

[jucole]

I'm very much a beginner at electronics but surely such an experienced team would provide more details to the individual module specifications?  for example the oscillscope specification of 2 CH @ 125MS/s,  what would be the useable bandwidth?

[Bored@Work]

I'm very much a beginner at electronics but surely such an experienced team would provide more details to the individual module specifications?  for example the oscillscope specification of 2 CH @ 125MS/s,  what would be the useable bandwidth?

Usable? That also depends on the analog input stage. Maybe 25 MHz on a good day with a good input stage. Likely more like 12 MHz. The theory says 62.5 MHz, but you never have an absolute pure sin as input and two samples per cycle does show you nothing.

[alm]

The theory says 62.5 MHz, but you never have an absolute pure sin as input and two samples per cycle does show you nothing.

Don't confuse beginners with wrong definitions of bandwidth and the Nyquist-Shannon-Whatsthatthirdguy sampling theorem. Bandwidth is defined in terms of sinusoidal signals (any signal can be decomposed into a series of sinusoidal signals), so 60 MHz bandwidth does not imply that a 60 MHz square wave will be accurately represented. A 10 MHz square wave, maybe. And (a little over) two points is enough for sin(x)/x interpolation of a sinusoid (or a combination of sinusoidal signals up to the Nyquist frequency) and will give you a good representation of the signal.

The problem with applying the sampling theorem to DSOs is that it assumes a bandwidth-limited signal: no signals may be present beyond the Nyquist frequency. Analog input stages are not perfect: there will always be some higher frequencies leaking through, even if it's just noise. Sampling circuits are not perfect either. This both messes up the ideal interpolation. Limiting the bandwidth to say the sampling rate divided by 5-10 will (a) limit the amount of signal beyond the Nyquist frequency that gets through (since your input circuit will roll-off at lower frequencies) and (b) gives you more samples for the signals within the bandwidth, making interpolation easier. So I would say 25 MHz with a good input stage that attenuates any frequencies above 25 MHz, and 12.5 MHz for a lousy filter (watch out for aliasing in that case).

The 60 MHz they claim for the 'spectrum analyzer' suggests to me that the latter is the case.

[senso]

The target audience is arduino and RPi users, so dont expect much from it..
At 2:00 in the movie, Red Pitaya is so powerfull that it can debug arduino and Raspeberry Pi projects, oh yeah baby, feel the power 

[piranha32]

I emailed the Red Pitaya team yesterday asking what is the bandwidth of the antialiasing filters, but so far I haven't heard back. When I first read about the project I really wanted to back it, but the longer I think, the less I like it as a test instrument.
There is however one application that it may excel: as an SDR platform. It has high enough sample rate to cover the entire HF spectrum. Add some filters, PA and you have a decent quality pocket-size networked digital shortwave transceiver.

[EEVblog]

Does it have PGAs and trigger hardware?  Without those, it's not going to be much of an oscilloscope.

It's not an oscilloscope, it's a data acquisition and generation board.

[piranha32]

I emailed the Red Pitaya team yesterday asking what is the bandwidth of the antialiasing filters, but so far I haven't heard back. When I first read about the project I really wanted to back it, but the longer I think, the less I like it as a test instrument.
There is however one application that it may excel: as an SDR platform. It has high enough sample rate to cover the entire HF spectrum. Add some filters, PA and you have a decent quality pocket-size networked digital shortwave transceiver.

I've got a response:

Hi,
actual bandwidth is 60Mhz.

A bit too high for 125MSps. The filters do not look complicated enough to have very steep roll off, but even if they had, there would be a lot of phase distortion in the upper part of the pass band.
Anyway, even if it will not be a great measurement instrument, it is still a very interesting platform for signal collection and processing.

[Rasz]

looks like Analog Discovery at twice the price