What a crappy USB scope - Page 1
Forum section: electronics / testgear

author: ivan747
author_rank: Super Contributor
timestamp: June 19, 2011, 04:47:38 am
content: OK, I know they are actually crap, but I think my sound card input can do better than this!http://cgi.ebay.com/2-Channel-PC-Computer-Digital-mini-USB-Oscilloscope-/300544789091?pt=BI_Oscilloscopes&hash=item45f9dd8a63#ht_4792wt_802For US $33.95 you get:Benefits:2 channel input and synchronized display <-----Right, Iv'e never ever seen a scope that does thatRecords date, time and voltage in text file <-----I can haz a Rigol than can outputs teh CSV FIL3Measures range automatically <-----Auto mode is useless here because you can't use the scope at all!4 available modes:Low-pass filter mode, will get mains harmonics mode, computer crash mode and computer fire modeInput capture (trigger) functionAble to set any channel as the source of the capture (trigger) signal <-----Notice there is no external trigger.Able to set rising or falling edge to capture (trigger) signalAdjustable capture (trigger) signal levelPowered directly by USB port – no batteries or external power supply required <----- NO BATTERIES OR EXTERNAL POWER SUPPLY WILL GET FRIED, ONLY THE USB PORT WILL GET FRIED DIRECTLY.Use with electronic teaching equipment <----PERFECT FOR TEACHING WHY ENGINEERS SHOULD ADD INPUT PROTECTIONCarry out acoustic tests and research <----- AS LONG AS YOU DO IT IN COWS, WILL NOT WORK ON MICE, YOU WILL SEE WHY IN THE TECH SPECSIdeal for SCM developmentExamine and repair apparatus and appliancesTechnical Parameters:PC connection: USBOperating systems used: W2K, XP ,Windows 7(32bit) <----YOU KNOW IT'S CHINESE CRAP WHEN THEY CALLIT W2KSignal input: BMC connection with universal oscillograph probe <----MISSPELLED BNC, OR INVENTED A NEW CONNECTORMax sampling: 8kHz x 1/ (4kHz x 2) <------ I CAN PLUG A SPEAKER IN AND TELL YOU WHAT FREQUENCY IS ITVoltage: 5V USB port supplyCurrent: 60mAMeasurable frequency: 0Hz -----3kHz <------...DIV array: horizontal 16DIV x vertical 10DIVInput impedance: 1M?Max voltage: 0---5V <-----NOW I NEED ONE OF THOSE X100 PROBES. OH, WAIT, I CAN GET A REAL SCOPE FOR THAT PRICE...Error of voltage measurement: ±30mV <----- THAT'S 0.6% ACCURACY... AS LONG AS THEY THINK THE USB PORT'S VOLTAGE IS ±0.5%. DO YOU THEY THEY REALLY USE A VOLTAGE REFERENCE?Adjustable range of time domain: 10 mS/DIV----10800 S/DIV <----WHAT WE WANT TO LOOK AT IS TINY LOGIC SIGNALS, NOT THE VOLTAGE ACROSS A BATTERY BEING CHARGED. THAT'S WHAT DATALOGGERS ARE FOR.Error of time measurement: ±0.01%Capacity of data record & save: 8388608 x 2Max time of data record & save: 93 hours <------OR UNTIL THE CRAPPY SOFTWARE ALGORITHM FILLS UP YOUR RAMYeah, my very first forum rant

author: ivan747
author_rank: Super Contributor
timestamp: June 19, 2011, 05:09:56 am
content: By the way, what I do for not getting crap results out of eBay is search for:oscilloscope -vintage -nano -pocket -usb -digital -dso -avr -pic^For analog only Tek 465-ish scopes ^You can also add the "Used" filter on the left of the site.And I use:oscilloscope -vintage -nano -pocket -usb^ For anything useful ^You can add "-portable" for getting rid of unaffordable portable scopes. But the best way to solve that problem is to use the "Price" filter. Also be aware of the high shipping costs when shipping from China, avoid these "government surplus sale" items that end in hands of these online secondhand warehouses that have no idea about scopes and stick to the high end sellers. Get one with a picture of the scope working. If it's got technical specifications there's a good chance that the seller knows what's being sold. And if the seller is more inclined on giving only cosmetic information and telling you they "have no way of testing it" then it's probably one of those secondhand shops.

author: Zero999
author_rank: Super Contributor
timestamp: June 19, 2011, 03:24:48 pm
content: Someone at work was tempted to buy a 'scope like that for training he GCSE electronics students. I warned him off but I don't know whether he listened. I hope he did but don't I know because he left shortly. I didn't know him much but he did come across as the arrogant type.Are there any decent USB 'scopes?This one doesn't look bad: high resolution 9-bit per sample (better than many DSOs), 200MHz analogue bandwidth (probably only 100MHz is usable with both channels) and input over-voltage protection, although this is only 35V and probe ground is connected to the PC's protective earth. It's Windows only (so not and option for Mac or Linux users unless they use a VM) and there's no mention of whether Windows 7 is supported, although Vista is.http://www.hantek.net/Manual/5200A/DSO-5200AUSB_Manual.pdfhttp://cgi.ebay.co.uk/DSO-5200A-200MHz-PC-USB-Digital-Oscilloscope-VISTA-/260688504731?pt=UK_AudioElectronicsVideo_Video_TelevisionSetTopBoxes&hash=item3cb23ee79b

author: ejeffrey
author_rank: Super Contributor
timestamp: June 19, 2011, 03:48:43 pm
content: There are some reasonable USB based oscilloscopes, but they tend to be priced similarly to bench top units, or even higher. Gage makes some rather high end PCI and USB based scope modules but you don't want to know what the prices are.Their bread and butter is more for automated test setups and data acquisition than for general purpose debugging and product development.

author: ivan747
author_rank: Super Contributor
timestamp: June 19, 2011, 03:51:27 pm
content: Quote from: Hero999 on June 19, 2011, 03:24:48 pmI don't think so, the USB 2.0 bus is too slow to give anything useful. At 8 bit sampling the maximuum theoretical speed without protocols is 480/8 Mbps which is 60 megabytes/sec. If they used Firewire or SCSI or maybe USB 3.0 they might be decent, but I've never seen anything like that and if there are any they would cost a LOT of money.It's just like those custom PCI interfaces. I've seen PCI-I2C bridges at 500 dollars! And they come in 5V and 3.3V versions. That's just to charge you with twice the money! With 4 simple signal MOSFETS and 2 GPIOs you could have done the same. Total cost increase: $0.50 Total extra programming time: 30 minutes. Anyway, that doesn't have to do with scopes.

author: saturation
author_rank: Super Contributor
timestamp: June 19, 2011, 04:52:54 pm
content: Even if you had an automated test suite controlled by a PC, many traditional instruments can be network controlled, giving the user similar capabilities as a USB, or even PCI/e, etc., based instrument.Quickly looking at what's available, cost of a USB scope => of many bench type digital scopes; many others cost more and offer less capabilities.Maybe total demand of bus scopes makes these scopes less cost effective.http://www.home.agilent.com/agilent/product.jspx?nid=-33712.774931.00&lc=eng&cc=USNI is a leader in the PC controlled instrument sector:http://sine.ni.com/np/app/main/p/ap/mi/lang/en/pg/1/sn/n17:mi/

author: Simon
author_rank: Unknown
timestamp: June 19, 2011, 05:48:58 pm
content: I think the thing is that by the time you have built a decent USB scope you just need to add an LCD to it to have a standalone scope.The new USB3.0 standard may increase the performance of basic units. My rigol can pretty much function like a USB scope, useful if i want better screen resolution but otherwise I can use it in standalone mode. So why buy a unit without a screen unless you have a crazy space restriction ? USB scopes save you no money, not any more

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 19, 2011, 05:54:51 pm
content: Quote from: Simon on June 19, 2011, 05:48:58 pmNot sure - I think the problem is not so much bandwidth but unpredictable latency at the PC end. Last time I looked, 64M of SDRAM costs about a quid, so putting a decent sized buffer at the scope end wouldn't cost a lot more.

author: Simon
author_rank: Unknown
timestamp: June 19, 2011, 06:02:45 pm
content: SDRAM works at 200 MHz max ? so won't grab 1 GS/s but then if you can interleave chips (RAM module usually haveas the SDRAM bus is 64 bits that gets you 1.6 GS/s in theory so yea maybe but again would the control circuitry cost more ?

author: Mechatrommer
author_rank: Super Contributor
timestamp: June 19, 2011, 06:37:09 pm
content: Quote from: Simon on June 19, 2011, 06:02:45 pmit should cost..."rigol standalone" - ("everything else" - board) + extra SDRAM cost.with "everything else" = lcd + housing + psu + knobs + etc

author: Unknown
author_rank: Unknown
timestamp: June 19, 2011, 06:37:27 pm
content: Quote from: Simon on June 19, 2011, 05:48:58 pmTrue. Add to this the lower sales volume, and you've got a more expensive scope.Quote from: Simon on June 19, 2011, 05:48:58 pmI don't see why. The average LCD in a cheap scope does maybe 20fps * 320px * 240px = 1.5Mpix/s. The display is often 1bit per pixel on cheap scopes, so 192kB/s would be enough. It's not like there is some big FPGA controlling the screen that can handle hundreds of megabytes of data. You just need some acquisition memory, like in stand-alone scopes.Quote from: Simon on June 19, 2011, 05:48:58 pmDid they ever?

author: Simon
author_rank: Unknown
timestamp: June 19, 2011, 07:07:08 pm
content: Quote from: Mechatrommer on June 19, 2011, 06:37:09 pmwell that's true, but I'd happily pay +30% for a standalone unit, with the option to connect it to a pc

author: ivan747
author_rank: Super Contributor
timestamp: June 19, 2011, 07:09:14 pm
content: Quote from: Simon on June 19, 2011, 07:07:08 pmYeah, I'm already sick of having my programmer and it's USB cable hanging across the room.

author: Simon
author_rank: Unknown
timestamp: June 19, 2011, 07:12:50 pm
content: convert it to wireless

author: ivan747
author_rank: Super Contributor
timestamp: June 19, 2011, 07:16:32 pm
content: Quote from: Simon on June 19, 2011, 07:12:50 pmIf I had the source code for the PICkit 3...For all that effort I could make a PCI > wireless USB bridge and develop drivers for them. Add an external antenna attachment, an optional signal amplifier and voilá, a $5000 "speciallized field test equipment".

author: Simon
author_rank: Unknown
timestamp: June 19, 2011, 07:28:26 pm
content: Quote from: ivaneduardo747 on June 19, 2011, 07:16:32 pmthere you go, and that's 5% of every sale commision to me for the idea

author: tinhead
author_rank: Super Contributor
timestamp: June 20, 2011, 09:47:31 pm
content: soon Cypress will have FX3 chips available. The FX3 GPIF bus (32bit) is running with 100MHz, that's enoughfor real time 400MSs usb dataloger/scope or 32port 100mhz logic analyzer, that's should be enough for most ppl.Of course it is BGA chip, so i'm not expecting so many cheap china/whatever scopes/logic analysers.

author: ivan747
author_rank: Super Contributor
timestamp: June 20, 2011, 09:54:16 pm
content: Quote from: tinhead on June 20, 2011, 09:47:31 pmI like when semiconductor manufacturers set the bar high. It is hard for Chinese cloners to make cheap clones with poor performance out of these parts.

author: EEVblog
author_rank: Unknown
timestamp: June 21, 2011, 12:50:37 am
content: Quote from: Hero999 on June 19, 2011, 03:24:48 pmYes, but they are usually quite pricey. Even Agilent makes them.Picoscope make some good ones, and CleverScope come to mind.Dave.