I need help to build a simple oscilloscope! - Page 1
Forum section: electronics / beginners

author: Azhar
author_rank: Regular Contributor
timestamp: August 08, 2013, 11:22:07 am
content: I'm so much in need for an oscilloscope and since they are expensive I thought maybe I might be able to build one that can, at least show me the wave forms.Are there any recommended designs for an oscilloscope that can be used with a CRT TV maybe?any schematics?Thanks

author: Rerouter
author_rank: Super Contributor
timestamp: August 08, 2013, 11:29:09 am
content: if you are looking at very low frequencies, e.g. under 50Khz, you may be able to get away with a CRT, it involves breaking into the coil drivers, and building a triggering circuit,you have the trigger circuit drive a sawtooth ramp based on the desired sweep speed, controlling the horizontal, and a switchable attenuator followed by an amplifier controlling the verticalthe reason for such low frequencies is that crt's are coil driven so take time to recover from a given input, whereas most analog scopes make use of electrostatic deflection plates,Edit: while i appreciate the methodology of wanting to make one on your own, your in aus, you can get some old analog gems for under $50, pick up,

author: kripton2035
author_rank: Super Contributor
timestamp: August 08, 2013, 11:31:49 am
content: look around in this forum, be patient, look at ebay, you can find a used decent scope for $50 (Dave had one for $19 !!!)I dont think you can build one scope yourself for less than $50and if you can it will be less featured than the $50 used one.also for nothing you can have a scope on the audio card of your pc computer, limited to low frequency, but free.

author: EEVblog
author_rank: Unknown
timestamp: August 08, 2013, 12:01:22 pm
content: Circuits that turned your TV into a CRO were very popular in the 70's. Lots of magazine articles in the archives if you go looking. Google "tv oscilloscope"

author: dfmischler
author_rank: Frequent Contributor
timestamp: August 08, 2013, 12:57:19 pm
content: I converted a B/W TV to a scope when I was a teenager in the late '70's. Mine was untriggered and not calibrated worth a damn (OK, it might have been a little flaky, too). A PC soundcard oscilloscope would have been a big improvement. If I had known where to get a real triggered scope for $50 I sure would have.

author: Legit-Design
author_rank: Frequent Contributor
timestamp: August 08, 2013, 01:32:10 pm
content: http://www.serasidis.gr/circuits/AVR_oscilloscope/avr_oscilloscope.htmRemember similar project on a russian forum which used separate AD converter, I think it had atmega, color display, 8bit parallel connected adc, with all the sources available. It was named Chameleon, or something similar in cyrillic.EDIT: Found itReally simple single layer pcb, can be etched at home.http://radiokot.ru/circuit/digital/measure/30/use google translate, I use the one embedded in Chrome, works really well.Quotehttp://radiokot.ru/forum/viewtopic.php?f=25&t=19878&hilit=%D0%A5%D0%B0%D0%BC%D0%B5%D0%BB%D0%B5%D0%BE%D0%BD&350 page forum thread discussing the thing.ADC datasheet:http://www.analog.com/static/imported-files/data_sheets/AD9280.pdfHaven't myself built either of those, yet...http://accrochages.drone.ws/en/node/90some arduino oscilloscope alternatives, more can be found...

author: kripton2035
author_rank: Super Contributor
timestamp: August 08, 2013, 02:22:33 pm
content: @Legit-Design:nice simple design, but it will surely cost near $50, and a lot of time to build itand as I said the specs are far beyond a 20MHz analog scopeand the inputs are not protected at all ...

author: ddavidebor
author_rank: Super Contributor
timestamp: August 08, 2013, 02:58:21 pm
content: Quote from: Azhar on August 08, 2013, 11:22:07 amI've an oscilloscope actually at 1€ on ebay XD

author: Paul Moir
author_rank: Frequent Contributor
timestamp: August 08, 2013, 04:15:24 pm
content: I don't know why you would bother with a TV oscilloscope when you can get there with a PC soundcard type oscilloscope. I guess it would be possible to get DC on the TV one, but that is some extra work.Google "Sound card oscilloscope" or xoscope.But an old CRO is the best way. Even a 5MHz vacuum tube type if you look around local. Those ought to be free. I got by with an old heathkit one for years.

author: dfmischler
author_rank: Frequent Contributor
timestamp: August 08, 2013, 04:22:30 pm
content: Quote from: Paul Moir on August 08, 2013, 04:15:24 pmFor electronics use, yeah. Some guy was hawking an old RCA untriggered scope at a local flea market recently who wanted 40 bucks for it "because of its cool retro look"Barnum's law says that he will probably eventually sell it.

author: free_electron
author_rank: Super Contributor
timestamp: August 08, 2013, 05:17:38 pm
content: Quote from: dfmischler on August 08, 2013, 04:22:30 pmThat's it. i am buying my own island somewhere in the pacific where i will set up a fully equipped lab under the palmtrees. goodbye world . I've had enough of the morons in this world.

author: KedasProbe
author_rank: Frequent Contributor
timestamp: August 08, 2013, 05:40:03 pm
content: A project that I saw when I was checking for STM32F3 projectshttp://tomeko.net/miniscope_v2d/Trying to get some luck on ebay seems like a better plan though.

author: tinhead
author_rank: Super Contributor
timestamp: August 08, 2013, 05:45:03 pm
content: very simply design:1. take something like this - ebay 2513141647742. set scale to the middle3. rotate the case by 90°ready!when you need strorage oscilloscope add a small pen a piece of paper - ready.Such design is "green", retro looking, cheap, lightweight, pure analog (with pure analog storage)!EDIT: wondering now how long it takes to see first chinese clones of my scope ^^

author: ptricks
author_rank: Frequent Contributor
timestamp: August 08, 2013, 07:27:30 pm
content: If you just want to see low frequency stuff then use a sound card interface. It isn't ideal but it can show waveforms fairly well. I used one once to record IR remote control signals. Simply connect the output of a standard 38Khz ir module to the line in .http://www.lirc.org/ir-audio.htmlhttp://zelscope.com/

author: c4757p
author_rank: Super Contributor
timestamp: August 08, 2013, 07:31:27 pm
content: Quote from: tinhead on August 08, 2013, 05:45:03 pmI found one!!

author: free_electron
author_rank: Super Contributor
timestamp: August 08, 2013, 08:26:39 pm
content: it may actually be cheaper to hire someone in china, give him a pen and paper and have him draw the waveform for you ...

author: MrAureliusR
author_rank: Unknown
timestamp: August 09, 2013, 12:08:36 am
content: free_electron is not far off... you could hire a whole team to draw animated waveforms!but seriously, I looked into building a basic 'scope' using an old CRT TV... and basically, it ends up being useless. Yeah, you can see a waveform, but whoop-dee-doo, you can't take any measurements, there's literally nothing you can do but sense the presence or absence of a waveform. Trust me, you're going to want more functionality than this!

author: TerminalJack505
author_rank: Super Contributor
timestamp: August 09, 2013, 12:44:43 am
content: ...and, ironically, you will most likely wind up needing an oscilloscope to debug your homemade oscilloscope circuit.

author: ivan747
author_rank: Super Contributor
timestamp: August 09, 2013, 01:16:18 am
content: Quote from: tinhead on August 08, 2013, 05:45:03 pmPffft...True compact analog storage and playback and dual channel, just attach 2 pens:http://i382.photobucket.com/albums/oo269/CrowLogik/AKAIPosingsm007.jpg

author: Azhar
author_rank: Regular Contributor
timestamp: August 09, 2013, 06:46:52 am
content: Quote from: ddavidebor on August 08, 2013, 02:58:21 pmYou must be joking!!

author: Azhar
author_rank: Regular Contributor
timestamp: August 09, 2013, 06:52:45 am
content: Quote from: Paul Moir on August 08, 2013, 04:15:24 pmBecause I already have an old 5" crt tv, and I thought it would nice to use it as a scope! but now I changed my mind, after reading all the replies I realized even if I build one it would be a useless oscilloscope!

author: IonizedGears
author_rank: Regular Contributor
timestamp: August 09, 2013, 07:14:53 am
content: Well, pretty useful if all you need is the shape of a waveform but for measurements, you would have better chances with a potato.

author: poorchava
author_rank: Super Contributor
timestamp: August 09, 2013, 08:04:28 am
content: You could fiddle around with microcontrollers and build your own DSO. There's a guy on polish electronics forums by the nicknamedrzasiekwho builds miniature scopes around popular microcontrollers. You can see a translated description here:http://www.edaboard.com/thread218091.html. There's also his webpagehttp://www.drzasiek.cba.pl/oscyloskop3.php(you will need translator for that).Anyway, many microcontrollers nowadays have high bandwidth ports or quite fast ADCs:-stm32f407 found in discovery boards has 3 adc which can be interleaved for up to 7.2MSPS (and since it's a SAR type ADC you can overclock it to achieve higher speed but lower reqolution - nominal is 12 bits).-arm microcontrollers often have external memory interface for connecting external flash or ram, but they can quite often be reused as fast and DMA enabled data i/o-PICs have a thing called PMP (parallel master port). Notable pic32's should be able to run that port at rather high rateI will not be high spec, but it's better than nothing

author: ddavidebor
author_rank: Super Contributor
timestamp: August 09, 2013, 09:22:54 am
content: Quote from: Azhar on August 09, 2013, 06:46:52 amNow is 1.5€

author: M0BSW
author_rank: Frequent Contributor
timestamp: August 09, 2013, 10:32:23 am
content: http://www.instructables.com/id/How-To-Make-A-CRT-TV-Into-an-Oscilloscope/There's loads more on google and you tube

author: ignator
author_rank: Regular Contributor
timestamp: August 09, 2013, 01:14:10 pm
content: Quote from: Azhar on August 08, 2013, 11:22:07 amYou have a PC, look on eBay for a USB oscilloscope. Find one that has the bandwidth and price you can afford. Some may come with the source code, so you can add your own features.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: August 09, 2013, 01:35:04 pm
content: Quote from: MrAureliusR on August 09, 2013, 12:08:36 amUnfortunately this is also pretty true of most older vacuum tube era oscilloscopes. Even the old textbooks refer to an oscilloscope as something that lets you visualize a wave but not really measure it; primarily a qualitative instrument. Then Tek came along and fixed that.

author: Legit-Design
author_rank: Frequent Contributor
timestamp: August 09, 2013, 01:41:28 pm
content: Most of usb oscilloscopes are crap, especially the cheap ones.Most of the advertised specs aren't even true.If that holds true for scopes which cost the same as true digital scopes, are the even cheaper ones even worth considering.There might be exceptions, but usually they cost more money. Is it worth spending money on something that is almost certainly toy/useless, when for little bit more money there are serious tools available?

author: ignator
author_rank: Regular Contributor
timestamp: August 09, 2013, 07:56:08 pm
content: Quote from: Legit-Design on August 09, 2013, 01:41:28 pmNote that Azhar, the OP, can't afford any COTS scope. So this OP was looking to make one. For $20 you can get a 8K sample USB scope. I bet it's junk. I have no clue what the OP is trying to measure. I didn't see anyone ask about that. But I doubt if a homemade TV scope in the end would have any more bandwidth then the lowly-est of dirt cheap USB purchased from any China vendor. And if one was found with source code, the OP would get all the learning fun they would ever want.So Azhar, what is your budget? What are you trying to measure? Do you have an idea of what bandwidth you want? Do you need a storage scope?

author: Unknown
author_rank: Unknown
timestamp: August 09, 2013, 08:38:07 pm
content: It should be possible to find an old analog scope for $20. Even Dave managed to. Even an old tube-based beast (eg. Tek 5xx series) will be a lot better than a crappy DSO or TV-based scope.

author: Sigmoid
author_rank: Frequent Contributor
timestamp: August 09, 2013, 11:48:32 pm
content: Quote from: ignator on August 09, 2013, 01:14:10 pmWell... He has a PC. That has a sound card.Next, get a freeware sound recording software that lets you zoom in on the waveforms.Then, hack together a basic high pass filter and a voltage divider to get AC coupled line level input.Tadam, 4kHz DSO!As good as (or better than) anything you can build at home using microcontrollers. Of course a $50 old analog beast will leave it standing, but hey, it's free.

author: Azhar
author_rank: Regular Contributor
timestamp: August 11, 2013, 01:27:38 am
content: Quote from: alm on August 09, 2013, 08:38:07 pmTrust me I tried! I have no luck with ebay!

author: Azhar
author_rank: Regular Contributor
timestamp: August 11, 2013, 01:47:28 am
content: Quote from: ignator on August 09, 2013, 07:56:08 pmI need a scope to start with, i.e to use it as a beginner, I am studying electronic engineering at uni but I don't have access to the uni lab all the time, therefore I need one on my bench at home!Now I realized it is better to find an old scope than building one yourself, esp with an old crt tv! after searching and reading I found out it's gonna be useless!Anyway thanks to you all. it was very helpful and interesting to read all your replies

author: kripton2035
author_rank: Super Contributor
timestamp: August 11, 2013, 08:00:14 am
content: Quote from: Azhar on August 11, 2013, 01:27:38 amwith ebay it's not a question of luck (sometimes yes) but mainly of patience !make automated searchs to warn you by email as soon a something you want is outthen follow it, note the prices, and then if something similar pops out, you know with some precision the final price.you can also use a nice program like auctionsieve to search for what you need

author: Unknown
author_rank: Unknown
timestamp: August 11, 2013, 01:14:20 pm
content: Local pickup will often get you better deals, especially for large, heavy scopes that are expensive to ship. Try your local equivalent of Craigslist. Of course this is somewhat dependent on the population density and type of industry in your neighborhood.

author: Azhar
author_rank: Regular Contributor
timestamp: August 13, 2013, 01:21:47 am
content: Quote from: kripton2035 on August 11, 2013, 08:00:14 amThanks for the advice! will try this prog

author: Azhar
author_rank: Regular Contributor
timestamp: August 13, 2013, 01:27:34 am
content: Quote from: alm on August 11, 2013, 01:14:20 pmI tried such sites! and the cheapest I found is $170http://www.gumtree.com.au/s-ad/hawthorn/other-electronics-computers/oscilloscope-bwd-826-50mhz-2-channel/1024681672

author: Unknown
author_rank: Unknown
timestamp: August 13, 2013, 02:49:47 am
content: Patience may be helpful, a better deal is bound to come along.

author: Sigmoid
author_rank: Frequent Contributor
timestamp: August 13, 2013, 02:59:53 am
content: It's a good idea to use the ended listings function on eBay, that will give you a realistic idea of the price ranges. My research results, for example:You can get a good Hameg for $50 or less, but you may have to wait months for it (at least on the US site). With these rebadged white flashy BK Precisions, Tenmas and similar, you may need to wait significantly less for a bargain. For a Tek that's in working order, be prepared to shell out above $100. For an iconic Tek in good working order, $250-$500.Personally I just bought a Tek 2225 from a university surplus batch, all the controls are in place, no external damage, seller says is in working order and was in use until recently. He was selling scores of the things, most in far worse shape (knobs missing, etc... students are barbarians... XD) It was $130 with well below $20 for shipping. If it works good, that sounds like a fair price.

author: Dajgoro
author_rank: Frequent Contributor
timestamp: August 13, 2013, 04:59:17 am
content: Quote from: Azhar on August 13, 2013, 01:27:34 amHah, I was in the same situation, no scope, and nowhere to buy it.I found cheap ebay deals but shipping to my country would be more expensive than the scope itself!In the end I had to pay ~300$ for a local second hand one.

author: Azhar
author_rank: Regular Contributor
timestamp: August 15, 2013, 01:28:41 pm
content: Quote from: alm on August 13, 2013, 02:49:47 amwe have nothing other than patience!