My First ‘Proper’ T&M Instrument

I haven’t written in AEONS! And I figured, “Hey! What better way to begin my two-zero-one-zero archive than by bragging…..oops!….I mean blogging about one of my new acquisitions”. I’ve recently bought myself a DSO. Not the fancy Agilent or Tektronix scopes; I bought myself something much more affordable – a DSO2090. I’m pleased with it. Very pleased. And, since there are very few reviews about it online, I’ve decided to write one.

I had initially decided to build my own DSO, but as I soon found out, building test and measurement equipment is no child’s play. I tried in vain to get my hands on a decent ‘scope on eBay, but most of the scopes were out of my budget, and the ones that were in, wouldn’t ship to India. A lot of manufacturers make  USB scopes – PicoTech and BitScope being the notable ones. But again, too expensive. And I really got sick of trying to use my soundcard as a low cost ‘scope. So after much forum-trawling and  late night ‘research’ I settled on the DSO2090. Do note that the price of this instrument can vary from 160 bucks to over 300 bucks on the net!

The ‘2090 is a good piece of equipment. It’s priced reasonably well (obviously, a lower price would be better! :-P), and it has most of the functions that higher end DSOs have. A few words of warning – don’t expect the ‘2090 to match up to a dedicated bench DSO. The ‘2090 is more like a tool that the moderate-to-advanced-level hobbyist, rather than a test engineer at Texas Instruments, would have.

Ripped from the seller’s (www.getbetterlife.com) eBay page 

I still haven’t test driven the socks of the DSO, but I have managed to get my fingertips dirty. Read on for the lowdown.

The ‘2090 is a USB driven, two channel digital signal oscilloscope. Mine is a Hantek clone. It can measure at 100 megasamples per second (MSps), and has a bandwidth of 40MHz (for a nice explanation about the difference between sampling rate and bandwidth go here, and also read this).

Specs:

• 100MSps real time sampling
• 2.5GHz equivalent sampling (also called ‘ETS’)
• 40MHz (-3dB bandwidth)
• 8 bit resolution
• Max input voltage 35Vp-p
• Vertical deflection: 10mV – 5V @ 1x probe (9 steps)
• Horizontal deflection: 4ns – 1hr (38 steps)
• Trigger: external, or either channel (edge based, single, normal)

Software features:

• Several convenient measurements (P-P, frequency, RMS, etc)
• FFT/Spectrum
• Math (add, subtract, multiply, divide)
• Saving screenshots (JPG, BMP
• Logging (DAT, Word, Excel)
• Nice demo function
• Other useful features

I ordered my DSO2090 from a China-based site. The cost was the lowest from among all the web-based dealers, AND more importantly, shipping costs weren’t atrocious. The base price was USD161.20, and shipping was USD29.71, for a total of USD191.91 (~INR 9,324). Customer service on the site was very prompt and courteous. Shipping to Gurgaon, India, took a little long – 10 days. But in all fairness, it was the Christmas week. Packaging was very good, and the DSO came unscratched and unharmed. I had no issues with customs (both Bombay, and Delhi released the parcel in less than 3 hours).

Really good packaging

The box, and its contents

The scope is totally USB driven – no external power required. The cable supplied is a USB ‘Y’ type cable – One for power and data (black), and the second (red), to supply additional power, if necessary.

 
The ‘Y’ cable to the right and the BNC jacks to the left.

Two BNC clip probes and a few probe accessories come as part of the kit. The probes supplied are compensated 1x/10x probes. Considering the price, they’re very good quality.

Left: The Probes Right: One of the clip probes with its sheath pulled back. Also visible is the 1x/10x slide switch.

 
Close-up of the probes (from some site). The colour coded rings are really useful.

At the back of the scope there are two metal tabs – “Ground” and “Cal”. The calibration tab gives a 2Vp-p square wave at 1kHz.

 
The back of the probe on the right. The probe’s own calibration signal is on the right.

The body of the DSO is plastic, and build quality is fairly good.

As with almost all digital T&M equipment these days, the ‘2090 can be interfaced with custom software. As a bonus, sample C++, VB, and LabVIEW programs are included on the driver CD.

Below are a few screen shots of some measurements.

Power supply noise when my CFL table lamp turns on

A 50% 6.13kHz PWM from the Super Probe that I built some time back.

Brushed motor noise. The BEMF spikes when the brushes break contact are clearly visible. RPM of the motor is approximately 20000 RPM.

What the DSO2090 is NOT:

• a Tek or an Agilent ‘scope
• a full-fledged DSO with benchtop features
• a standalone device
• a super-accurate device that you can trust your life (or other’s lives) on

What the DSO2090 IS:

• an awesome hobby ‘scope with lots of features
• a very low price test and measurement device
• very portable
• a very cool device that will enhance your geek image

The final word? If you’re a poor student hobbyist like me, and have reached the stage where you ‘absolutely need’ a way of seeing what signals are zooming around in your circuit, then the DSO2090 is certainly for you. There are variants to the ‘2090:

• the DSO2150 (150MSps/60MHz)
• the DSO2250 (250MSps/100MHz)
• the DSO5200 (200MSps/200MHz)
• the DSO5200A (250MSps/200MHz)

I find that the ‘2090 is the best value for money, and it fulfils my need, at least for now :-D . A recommended buy for those looking to purchase a ‘scope.

To Do

If I remember correctly, my first introduction to circuits was in my 4th grade when my dad’s friend gave me a neat science-projects like kit. The kit contained components to teach the basics of electronics - switches, a buzzer, small incandescent bulbs (I absolutely dislike using these bulbs nowadays because of the power they drain), wires, steel wool, and other such things.

I was in the US at that time, and Lucas, a friend, and I, used to perform the ‘experiments’ given the handbook. I don’t know what Lucas’ dad did exactly, but to me he was some sort of god; he had tons of toasters and mixers and radios and TVs and machines lying open in his house. My mom would definitely have hit the roof had she seen such an untidy house. But I loved that house because, I suppose, it contributed a lot towards encouraging me to explore electronics as a hobby. And would you believe I’ve still got components from that kit!

In the 6th grade I read something about an FM transmitter and pestered my mum to take me ‘shopping’. I bought a couple of condenser mikes and speakers, but not knowing anything about transistors and chips, got absolutely nowhere. I did, however, manage to build a working crystal radio – very interesting things, I must say.

I always loved mechanics, and continued tinkering with small motors and toy cars and bulbs till the 10th grade. Finally, when I moved to junior college, I got my first formal introduction to electronics. I had loved the mechanical aspect of things, and could put my hand to anything that had gears and rods and levers. So junior college, with its electronics, was a new experience.

Every year I keep growing in experience and exposure, and my ‘To Do’ list keeps expanding. There are a lot of things that I want to build, but I’ve either not had the time or the knowledge to see them through. A lot of the things in the list are half complete; some of them have passed the proof-of-concept stage and are awaiting, to borrow from software lingo, the transition from beta to release version. Summer break is the perfect time to hit these projects with a vengeance, and I certainly plan to achieve a lot during these two and a half months.

The only problem – as I’m researching one project I invariably come across something new and attractive, which but naturally, gets appended to the To Do list, making it longer still!

Here’s my list, in current form:

Project	Status
Linear PSU	v3; Revision required
SMPS	Proof-of-concept
Home Energy Meter	To be done
Air Conditioner Controller	v1; Revision required
Computer Controller DMX	To be done
Ultrasonic Rangefinder	Proof-of-concept
Digital LC Meter	To be done
Temperature Controller for Soldering Iron	Proof-of-concept
Long Range Walkie Talkies	To be done; (searching for info)
Home Intercom Using Old Phones	To be done
Drill Press	To be done (currently collecting parts)
CNC Milling Machine	To be done (currently collecting parts)
iTrip Mod	v1; Working
iPod Mini Remote	To be done
Auto-balancing Inverted Pendulum	To be done
PIC to VGA	To be done
Optical Mouse Based Navigation System for Small Robots	Proof-of-concept
Very Long Range IR Transmitter	Proof-of-concept; (currently collecting parts)
USB PIC Programmer	To be done
Class D Audio Amplifier	v1; Revision required
Digital Weigh Scale	To be done
Low Cost USB Oscilloscope	Proof-of-concept
Nokia 3310 / 6610 LCD Interface	Proof-of-concept
CYUSB6934 Radio Interface	Proof-of-concept
Lightweight Multipurpose Robotic Platforms (to be christened ‘Saxiest’ :-D )	v2; Revision required (currently collecting parts)
Foot Speed Controller for my Dremel XPR	To be done; (searching for info)

As you can see, several projects still need to be started. Any advice/help/experience is most welcome :-)

Of Scopes and SMDs

I've always loved electronics for its 'minuteness'. I'm fascinated, even today, by how small consumer electronics can get. Have you ever opened up your cell phone or iPod and seen the myriad tiny chips and resistors and capacitors and whatnot? And do you realize that what you see is actually not small; it is HUGE when compared to what is on the inside of those silicon chips.

With Intel, using the 45nm process to manufacture its current processors, now talking about switching to the 30nm, and progressing to the 10nm fab, everything is set to get very, very small. The SMD resistors on your Nokia motherboard seem gargantuan in comparison.

Anyway, I absolutely needed to get myself a piece of this deliciously small pie. So in the past few months I've stared working with surface mount devices. Naturally, if I've reached the level where I'm working with SMDs, I would also have reached the level where I would need the services of an oscilloscope. Problem is, an oscilloscope, even a government-office-used, second-hand, two channel, 100MHz scope - the minimum demanded by any respectable hobbyist - costs about 10 grand. 10 grand is something I would like to have, but sadly, I don't. A new plain-jane CRO-oscope is about 25-30K, while (drool) Agilent DSOs start at a prohibitive 70K. Even cheapo entry-level USB oscilloscopes are a minimum of 10K, and to make matters worse, they aren't available in India.

So, like any other respectable hobbyist (all respectable hobbyists have what is called 'electronics-ego' - some may call it a touch of madness, others, an obsession, and yet others, an incurable disease; to hell with you, you vile naysayers! May you all burn!). Umm, yes, where was I? Aah, as I was saying, like any other respectable hobbyist, I decided to go the DIY way, and build my own scope.

The advantages of building your own scope - it's dirt cheap, and you learn a ton of other stuff (analog layout design, ADC nitty-gritties, USB firmware coding, and host data-handling to name just a few).

The scope would follow this kind of layout:

(Analog front end) --> (Data packaging for USB, on the PIC) --> (Host data display)

AFE:

(Buffer) --> (PGA) --> (Hardware AA) --> (High speed dual-channel parallel-out ADC from MAXIM/TI)

PIC:
(PIC 18F4550)

-> (8Mbit memory from Cypress, for deep capture)
-> (External trigger sources)
-> (USB2.0 Full speed @ approx 1.2MBytes/sec bulk transfer)

Host:

(LabVIEW software frontend)

Upto now I've built, and tested various parts of the AFE - I still need to throw everything together, and see if I actually get the desired results (this, without a doubt, is the biggest thorn in any engineer's side; everything works perfect in the lab, it works well as individual modules, and then, when you try to put stuff together, it all just falls apart. You start swearing and tearing your hair out in frustration; that's the reason why I'm.....uuh, forget it).

Last night (in Sid's words, and CCS-C) I was on cloud [unsigned int8 cloud 0b00001001]. I got USB bulk transfers to work with LabVIEW, albeit, in a crude way. Nevertheless, it worked, pleasing me tremendously. LabVIEW makes development super-easy. Easy, in a way that makes you feel dumb. Amit Sabne, who I've been brain-storming with, puts it very concisely - "Yaar, feel hi nahi aati!" - which is kind of true. The chaps at NI have done a great job of making hardware interfacing a snap. Wait for your USB device to enumerate, enter its VID and PID (device/manufacturer specific 'serial numbers'), throw a few icons and VIs here and there, and voila! You have délicieux transferts de USB bulke, served hot! (yes, translate.google.com is most helpful). The NI engineers have robbed hardware-software hackers from the trials and tribulations of mind-messing driver-writing, back-breakingly long hours of prouring over hardware, and sleepless red-eye-rubbing nights. Damn! Where's the joy and satisfaction if you can do something in 10 minutes, what used to otherwise take hours?

Now that I've got a rough and dirty implementation of PIC to USB transfers to work, what remains is putting it all together. Gimme a few days, and I'll upload the PIC firmware in CCS-C, and the LabVIEW VI here for you to use, enjoy, redistribute!