Products > Test Equipment
SainSmart DDS120 & DDS140 USB Oscilloscope
<< < (14/84) > >>
psynapse:
Ganzuul

"ENCb is left floating" Is that by measurement or by looking at the photos? 

I had made the assumption that ENCb was directly connected to ENCa by straight extension of the PCB track under the device itself:- the ENCa and ENCb pins are directly opposite one another on the chip.  Next time I get the chance I will measire resistance between the two pins.  I would expect this for the 120, its lower sampling rates mean the both A/D can run synchronous.  I will be disappointed with the 140 if this is true, because it will mean that the two A/D are not run "phased" and the device will give nowhere near the claimed 200Msps.

The GPIF should be capable of sustained rates up to 10Msps, but I have asked somebody who has built a 10msps scope around the fx2 chip.  I await his reply.  Conceptually, his design is very close to the 120 (see http://www.triplespark.net/elec/analysis/USB-LiveOsci/ ) I also have an fx2 prototyping board ordered that will allow me to establish what the real situation is.

I await with interest your thoughts on graph theory and state machines, it may prove very useful.

Yes, if greater precision is needed,  the resistor chain would work well.
ganzuul:
ACK! You're right. The trace is connected underneath. Today is not one of my more lucid days.

I'll take a little time and be more thorough with the state diagram thing. Markov chains appear to be good way to get a conceptual foot through the door on that subject though. https://charlesleifer.com/blog/building-markov-chain-irc-bot-python-and-redis/ really drives it home for those who need an intuitive, hands-on approach.

I'll say more, soon.
psynapse:
All

Just had a quick and helpful reply from the guy who built the FX2 based scope that resembles the DDS120, to quote him

"Regarding data transfer: Back then when I did this USB scope
I used it to transfer data at 20 MBytes/s (2 x 10 MS/s) for
many seconds or even minutes with only occasional data loss.
Say, >90% that a some second long transfer had no loss. IIRC.

Computers were slower at that time (Athlon XP, single core)
and the type of chipset did matter. Most crucial was the right
type of software (e.g. fx2pipe) to handle the async IO."

I see those as really helpful and positive words.










ganzuul:
20 MB/s might still be plenty, even if we get those only by reducing the encode rate. Positive indication indeed. =)



It appears that the purpose of two of the 8-bit multiplexers is to attenuate the analog input, so one can simply connect the two channels and set the relevant bits correctly to get deeper resolution.



The FX2 implements the following ECC:
http://read.pudn.com/downloads107/doc/439463/ECC%20Algorithm_Toshiba_v2.1.pdf
Princeton has decided some ECC schemes may be used for compression:
https://www.princeton.edu/~verdu/reprints/Lossless%20Data%20Compression%20Via%20Error%20Correction.pdf

The GPIF does operate at one instruction per cycle, and it uses 128 bytes to store its 'waveform descriptors'. These bytes are modifiable at run-time, but not quite on-the-fly.

Some words about graph theory: Graph theory appears to provide a theoretical framework for reducing the complexity of e.g. a circuit of logic gates while retaining its truth table. However, this process of reduction is pretty much the heart of a Turing machine; NP-completeness, Gödel's Incompleteness theorems, and optimization. Fortunately, humans brains with their neural networks are really good at optimization problems.
So, incredibly, I remain hopeful about squeezing more information through the 40MB/s max I have heard about!
doctormord:
Could we do a simple bulk sample software on the current firmware yet?

Beside this, maybe the osciprime source could help to understand fx2lp firmware developing?

http://www.osciprime.com/?p=source

and

http://sigrok.org/wiki/Fx2lafw

The open source sigrok driver which implements logic analyzer functions with the help of:

https://github.com/djmuhlestein/fx2lib
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod