after a little thinking i decided to drop the FT2232H for the FT232R. the FT232R can get 3Mbaud, ~300Kbyte per sec while still using the easy virtual com port. for the buffer, even 4Kbyte per channel is enough. with 4Kbyte of buffer and 50MSPS sampling we get: 4Kbyte / 50MSPS = 80 uS sampling time. looking at 20Mhz you can save 80uS / 50nS = 1600 sine waves in the buffer! at 2Mhz its still 160 and at 200Khz you can fit 16 sine waves in it. and its always possible to divide the sampling speed, heck, else the CPLD gets bored.
with a 4Kbyte buffer and 300Kbyte/Sec speed you can update the screen 300KB per Sec /4Kbyte * 2 channels = 37,5 times a second. thats plenty :D the FT232 is cheaper, doesn't need the eeprom and crystal and all other parts that the FT2232H needs. the opamps are expensive enough. schematic for CPLD board should be done tomorrow.
And i am a bit further, got a schematic of the full inputstage, so inputstage + ADC's warning, picture is BIG: http://http://img18.imageshack.us/img18/9009/scopeinput08.png PCB with CPLD and memory will take care of all power supply's. the opamps will be the LT6200, LT6200-10 and probably an AD8065.
@brian i prefer the Altera programming enviroment over the xilinx one. i wanted to order this board but the shipping is a bit more then 40 dollars :( bit sad to pay 40 dollar shipping on a 60 dollar board.
i prefer altera parts because there programming environment is a bit better and a USBBlaster clone is quite cheap. also, have a look at the LPC1837and the LPC1788 from NXP, there quite interesting to, they have ethernet for example. i think you should also look at the IDE's for the microcontollers and not just the specs of them. the professional stuff like KEIL and IAR have a demo version that works up to 32K of code. the price for a full version is A LOT, far out of hobbyist reach. the LPCXpresso software goes upto 128Kbyte of code and costs 512 dollar for the 512K version and 999 for the full version. a bit less expensive but still far far out of hobbyist reach. and installing GNU ARM takes about a weekend of frustating linux commands and then it will probably crash ;)
hmm, crossworks is semi-afforable, personal license is 150 dollar. better then the 5000 keil wants so see :)
but free shipping @ farnell when you have 50 euro's or more (as individual) for mouser i have to order for 75 euro's and they ship from germany. so i still order my stuff at farnell, i can order via school most of the time so i dont have to order 50+ euro's but an order as individual isnt so bad, export shopping cart, email it to them. most of the time you get a confirmation the same day, pay them, email them that you payed and in 1 to 3 days you got you're parts.
my program is semi-working, it captures 1 second of data and opens that in excel. its not a real scope and its rather buggy. so i recommend you to write you're own program for it. i have 2 PCB's, i got a PCB for the FT2232 board from FTDI and a PCB with the ADC. warning, i used an 741 opamp in there, i was not sure what opamp was needed so its a placeholder. replace with any fast opamp (20Mhz+) and the PCB's are a total mess, there pure test PCB's, USE AT OWN RISK. http://www.MegaShare.com/3462810
bit late but i like this board, thinking about ordering one: http://www.terasic.com.tw/cgi-bin/page/ ... .pl?No=593 for 59 dollars (as student) its cheap and blazing fast, lot more Logic Elements, a G sensor (lovely :D) and an ADC. programmer onboard aswell, it looks quite neat. and look at that box, it looks amazing:
its a bit late but i still wanted to share this. i always use this cheap ass flux from ebay, they call it solder paste and it goes in a square box, its just 1,99. http://cgi.ebay.com/Advanced-Quality-ZJ ... 5644e9a6bd its quite sticky, i smear a bit on my PCB and all the SMD parts stick trough it, very easy
i had a testsetup like that, got me 6Msps of data, roughly 500Khz without Sin(x)/x Interpolation. with Sin(x)/x Interpolation 2Mhz should be possible. the downside is, as soon as you plug in an USb stick or external HDD and start copying things the bandwith from the FT2232 plummits. USB printer and printing a big file does the same.
USB2 is high speed enough for me :) the added price of a RAM IC is much much lower then a USB3.0 IC and 4 layer board. and USB3 looks a lot harder then just using a FT2232, FTDI has drivers available and i already worked with a FT2232 before. the FT2232 easily gets 10+ Mbyte per second, thats more then enough with 64K 16 bit RAM, tjhats just 128Kbyte of data.
party time, analog inputstage done in multisim: http://http://img148.imageshack.us/img148/2038/input.jpg in 2 weeks i will have a new scope, 4 * 250Mhz analog tek, then i can build the input stage and verify it in real life. for now i have to do with a multisim simulation but it looks promising. i will need some bad-ass opamps to reach 10+ Mhz so i used virtual ones for now. the 10X amplifier will be an LT6200-10, to make it easy i used the specs of an LT6200-10 for all the virtual opamps. the buffer wil be something like an AD8065 (really low input current and fairly fast), the one for the offset something like an LT1222 (fast enough) time to enter it in eagle together with the ADS830 and stuff. i think that i will make 2 PCB's one for analog and one for digital, analog one will have everything from input to ADC and the digital one will have the CPLD and FT(2)232
I got a block diagram. look at it. from the input there's a amplifier that amplifies the input 10 times and a resistor divider to divide the input by 100. all selectable so you can amplify the input by 10 or divide it by 10 or 100 or just keep it this way. http://http://img825.imageshack.us/img825/5711/blockdiagram.jpg any ideas, please post them :)
picture time: http://http://img809.imageshack.us/img809/4682/dsc02169p.jpg http://http://img121.imageshack.us/img121/2474/dsc02170y.jpg BRC electronics is the name we use for our project group on school ;) the PCB and soldering are ugly ugly ugly, we used the soldering over first but half the stuff didn't solder correctly so i redid every solder :( this connects to my breadboard, from breadboard to FT2232 to PC. 6Mhz sample rate, actually works. vb.net gets the data and puts it in a text file, text files goes in excel and i see some sine waves :)
got one ADS working :) had some free time and made a small PCB with a ADS830 and a fast opamp. it works, didnt test anything special, 8 digital I/O's to a logic analyzer. so i know how to connect the while stuff, next week more free time to make a full PCB :) will post a picture tomorrow
