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Messages - arakis

647
Project development, ideas, and suggestions / [Sugestion] USB 3.0 breakout board
http://www.edn.com/article/517788-USB_3 ... ations.php

It seems cypress is making a EZ USB 3 chips with embeded 200MHZ ARM926EJS  core, they should be on sale for less then 10$. IMO it would be cool to design a breakout board that could be sold with the chip soldered on it, since for many ball soldering is beyond DIY. 

A storng MCU like that with USB 3.0 embeded, would open doors to lots of high speed PC projects,like Logic analysers, DSOs, spectrum analisers, etc etc.
649
Logic Pirate / Re: Logic Shrimp variation
//end of off topic
Thanks ian, that helps alot, i expecialy like that you added how much of the CPLD is used up, excelent work. Id probably use one of those cheap spartan FPGA for more headroom and speed.
650
Logic Pirate / Re: Logic Shrimp variation
I have a similar idea, but for a dso, RAM+CPLD+FT2232+pic24+ADC
FT chip chanla A 245 sync would be conected to the cpld, Chanel B SPI would be conected to the pic, and the cpld would be conected to all, the cpld would do everything, the pic would set up the  trigering, data flow and start/stop, depending on the instructions from the FT2322. so basicly the PC would controll all.

-sorry for going offtopic
651
Logic Pirate / Re: Logic Shrimp variation
the datasheet on the pic says theat the timer1 gate can be driven trough the timer0 overflow, and this is all done trough hardwer, not trough inerupt, am i missing somethin
653
Logic Pirate / Re: Logic Shrimp variation
thatnks for a quick reply,
about the counter, couldnt a 8 bit timer0 be used to drive the Timer one thus giving 24 bit adressing or 16Mb per chanel
654
Logic Pirate / Re: Logic Shrimp variation
hi would it be posible to use different spi mem chips then the ones in the desingn, atmel's AT25DF041A has 4 Mbits adn a 70MHZ clk, and i think it is pin compatable, how dificult would be to change the code to take 4M of data insted 256k
656
Project development, ideas, and suggestions / Rise/Fall time measurment circuit
Hi, i would like to devop a standalone circuit that would measure rise and fall time, with the posibilty to measure propagation delay as well.

I have two ideas and would like you to point out witch would be more realistic, cheap, but still retain a resolution of 1ns.

both ideas require Ultra high speed comparatos to initiate measurment. one to start the measurment at 10%vcc, the other to stop it at 90%. thus create a impuse the lenght of the rise time.

idea 1, digital. (dont even know if it is posible to do low cost)
a 1GHz clock, that would tick a counter. controled trough the previus impuls trough a AND gate. by simply reading the count you get how many ns have passed. maybe a 500mz could be used with a counter that counts on bouth  the rising and falling edge.

idea2. analog. the impulse activate a constant current source that charges a capacitator, by measuring the voltage you chould get a liner representation of time, again I am unsure if there are fast enough op amps, or switches that would alow this to be developed cheaply. all imput is very welcome. here a opamp integrating circuit seems posible, but it would have to be ultra fast.
658
Project logs / Re: USB Scope
about your original scope with 1MSPS you can easily get 400KHZ spectrum out of it, by using software, search the net about fast furier transform, oversampeling, and digital filtering.

By defiiniton any signal that is sampled at a freq. Fs can be reproduced fully up to the freq Fm = Fs/2 by simply adding a low pass filter with a freq max at Fm. of course you have to add a input fillter as well that cuts of any freq higher then Fm.

once the signal has been sampled and is in your computer you can reproduce it on the screen using varius digital filtering tehniques and fft.

here is an explanation without the math of how it works.

when you sample a signas with a maximum freq Fm with a freq Fs = Fm*2, the spectrum of the resulting signal is a copyied spectrum of the original and pasted all over the infinit spectrum at Fs intervals.
you get a signal that has the original signal at 0->Fm, at Fs->Fs+Fm, 2Fs->2Fs+Fm............*well actualy there is a neg. component but lets not get into it as it is not important. so to retrive the original all you have to do is cutt off all the higher componets then Fm. the cool par is that all this can be simulated in a computer.

in other words a signa with a spectrum od 0->4KHZ sampled at 8Ksps can be fully recoverd on the output be it a DAC circuit or the screen of a monitor, all the information about hte signa is inside those samples, in other words the resolution at witch you can display it on a monitor can theroeticly be infinite!
-even thoug you only get 2 samples per cycle of the original signal, you can show on your screen 1000 samples, per cycle.
Fs=FM*2 is the theretical margin, but since input filters can never be perfect, and if any component above Fm get trough they will generate error in the resulting signal so it is easier to use Fs = 2.5 * Fm, and a cheaper filter with a lower slope.
 -sorry if this was rant, but i thought all DSO and computer oscilator projects should know that they don't need 100 samples per cycle to show the signal properly on the screen. 3 is more then enough, 10 -15 is more then enough even for sqare waves!

PS. the input filter is a must, and in many ADC circuits the most expensive part of the circuit.
P.S.S that means that with a 50MSPS you can show 20 MHZ signals on your scope with ease.

full math and explanation can be fount at this sites
http://www2.tek.com/cmswpt/tidetails.lo ... 4295&lc=EN
near the bottom under
How Sin(x)/x Interpolation Works

http://www.johnloomis.org/ece561/notes/ ... nterp.html
http://health.tau.ac.il/Communication%2 ... nting.html

of coure all this is in Spectrum, and since only sine wawe have a single spectrum defining them the above is the sine wave cut off point, square waves have many harmonics and to display it as square would require a lot of them, so the freq of a well shown square wave will be lower than that of the sine wave, about 7 times for 4 harmonics to be shown.

this is an image of a 4 harmonic square wave
659
General discussion / Re: Homemade flux
during prepwork and rubing it on the pcb it smells like nitrocellulose thinner , while soldering it smells like chalifonium, but less then when diping a tip into pure cali. its not a bad smell, it has a somewhat sweet smell, but then again i might be too used to it, BTW i use califonium paste(used for tining the tip) disolved in the thinner, it smells like the califonium paste in lower concetration.

I found thin on the net

When heated above the melting point of the solder rosin will fume and can be breathed in by the operator. This can lead to occupational asthma or make an existing asthmatic condition worse.

but that I think that refers to people who solder large amounts daily