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piglet
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"Unfortunately, I do not have a scope, nor does anybody I know."

Fri Oct 05, 2018 10:34 am

https://www.raspberrypi.org/forums/viewtopic.php?f=29&t=214661&start=25#p1323241 wrote: Unfortunately, I do not have a scope, nor does anybody I know.

The only tool I do have, is a digital multimeter my uncle gave me.
I read this today and I totally relate to it. Any time I try and build something and run in to problems I do a search on the internet... Actually, I should rephrase that: Any time I try and build something I run in to problems and do a search on the internet...

When I do this I find very helpful information, normally backed up by someone showing a 'scope trace showing what's going on.

Like the OP, I just have a cheap multimeter that just about tells me a rough indication of average voltage, continuity and resistance.

I have a hankering to see what's going on but a very tight wallet and don't know what I can cheaply buy that's actually worth having as an occasional tinkering hobbiest.

I'd like to be able see:

1) brownouts or spikes happening - handling supply for 3.3v and 5v up to a little over 12v (for 12v LED Strips controlled from pi)

2) wave forms that may not be as stable as intended or doing what I think - possibly audio, but definitely 3.3v and 5v PWM both sides of logic level converters

3) logic capture - again 3.3v and 5v to debug communication - serial and i2c perhaps?

I see things starting from a DSO138 for £11 all the way up to half an arm and one leg things that wouldn't be out of place in a research physics lab but don't know where to start in choosing something at the bottom end that can do these things well enough to be worth having.

Any advice would be gratefully accepted

drgeoff
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Re: "Unfortunately, I do not have a scope, nor does anybody I know."

Fri Oct 05, 2018 11:12 am

I have a DSO188 (currently on offer from Banggood for £20). Claims 1 MHz bandwidth which is fine for audio and low speed logic but only single channel and extremely limited triggering options. And being battery powered can be connected to circuits that are not mains isolated.

For "heavier lifting" I'm very pleased with my Rigol DS1054Z. 4 channels 50 MHz but there is a software hack that ups that to 100 MHz and enables many other options. Has protocol analysers for I2C, RS232 etc. Incredible value if you can afford £370.

For logic capture the £5 Salae and USBee clones on ebay are a useful addition to your toolbox.

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joan
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Re: "Unfortunately, I do not have a scope, nor does anybody I know."

Fri Oct 05, 2018 12:30 pm

For the digital side http://abyz.me.uk/rpi/pigpio/piscope.html can provide useful diagnostic information.

W. H. Heydt
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Re: "Unfortunately, I do not have a scope, nor does anybody I know."

Fri Oct 05, 2018 1:48 pm

I have a book in the house that has a full circuit diagram for building a 'scope... Two caveats, though, it only goes to (IIRC) 30KHz and it uses vacuum tubes. (The book was published in 1947.)

vinnieb
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Re: "Unfortunately, I do not have a scope, nor does anybody I know."

Fri Oct 05, 2018 4:41 pm

I had alot of fun building the dso138, and learnt alot about the circuitry involved through hours of troubleshooting why it wasn't working. There's some mods to improve it further, and some firmware alternatives too I believe.

I haven't actually used it much for real applications yet, but for the low price it's already paid for itself in the learning. Just make sure you get a legit one rather than dodgy copy.

Heater
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Re: "Unfortunately, I do not have a scope, nor does anybody I know."

Fri Oct 05, 2018 5:54 pm

It's amazing how much circuit debugging one can do without a scope.

Way back in the 1970's when I was building digital circuits with TTL chips as a teenager I would be tearing my hair out and ready to throw the whole project in the bin. Luckily my father, who was no engineer, said "Why don't you listen to it?". I did exactly that with a cheap crystal ear piece, sure enough I could hear things ticking and singing as expected, or not, and soon had my project working.

That won't work for high frequency signals of course. But that's just a question of using a TTL chip or two to divide the frequency down. Then listen to it.

Even the humble logic probe built with a logic chip and LED can tell you a lot. With two LEDs, one that lights on a high signal and another that lights on a low, it's possible to estimate pulse width ratios even at very high frequencies.

Listening to a circuit with a radio can tell you a lot.

With a little effort one can use a Pi as logic analaliser up to a few megahertz. Use one Pi to debug another!

That's all well and good til you get to analogue circuitry...

It is possible to pick up a good old CRT scope for very cheap on ebay. Which in many ways is superior to a modern digital scopes.

But I do love my Rigol DS1054z. Four channels and up to 50MHz for a stunningly low price. Even better that I could hacked to work at 100MHz.

It's well worth saving up for a decent scope.

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DougieLawson
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Re: "Unfortunately, I do not have a scope, nor does anybody I know."

Fri Oct 05, 2018 9:22 pm

Heater wrote:
Fri Oct 05, 2018 5:54 pm
But I do love my Rigol DS1054z. Four channels and up to 50MHz for a stunningly low price. Even better that I could hacked to work at 100MHz.
There's the World's most annoying Aussie who seems to agree with you.
https://www.youtube.com/watch?v=ETCOhzU1O5A
Note: Having anything humorous in your signature is completely banned on this forum. Wear a tin-foil hat and you'll get a ban.

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Heater
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Re: "Unfortunately, I do not have a scope, nor does anybody I know."

Fri Oct 05, 2018 9:47 pm

Hey, why the bashing on Dave Jones? Currently my favorite Aussie. A lot less annoying that millions of other people. Dave does not push himself in front of you face to annoy you. You have to actively seek out and watch his videos and such to even get a chance for him to annoy you.

And yes, the EEVBlog forum is a great source of info on hacking Rigol scopes and much else beside. https://www.eevblog.com/forum/

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DougieLawson
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Re: "Unfortunately, I do not have a scope, nor does anybody I know."

Fri Oct 05, 2018 9:57 pm

I think I know what I want for Xmas. I think Dave "Annoying" Jones may have pursuaded me. I like what he says, I just hate his voice and the inflection at the ends of sentences.

My favourite Aussie is my grandson (he's got dual nationality) who was born in Perth, WA in June 2017.
Note: Having anything humorous in your signature is completely banned on this forum. Wear a tin-foil hat and you'll get a ban.

Any DMs sent on Twitter will be answered next month.

This is a doctor free zone.

LTolledo
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Re: "Unfortunately, I do not have a scope, nor does anybody I know."

Fri Oct 05, 2018 9:59 pm

During my college days when we were building a "micro-controller" based on Zilog Z80 on breadboard, we have no access to oscilloscope to help us debug problems with the signalling and/or state of the IC pins. Most of the debugging were done at home (mine or other member's) and not at the university. None of us nor anybody we know outside the university has an oscilloscope at home.

the only thing we have (and as recommended by our professor then) was a DIY indicator based on 2 inverters of 74LS04 and 2 LEDs, mounted on "tongue depressors", to indicate "1" or "0" and even "tri-state",

Helped us debug the breadboad circuit until we got it running properly according to the program (in ROM).

might build one again soon....
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Come to me with 'problems' and I'll help you find solutions"

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Heater
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Re: "Unfortunately, I do not have a scope, nor does anybody I know."

Sat Oct 06, 2018 7:20 am

Congrats on you new favorite Aussie Dougie.

That's the way to start LTolledo, sounds similar to what we did building a Motorla 6909 board using wire wrap in 1980. That kind of logic probe is what I was getting at above. There are hundreds of simple circuits for such probes on the net. For example:

https://www.allaboutcircuits.com/projec ... gic-probe/

https://www.edn.com/design/test-and-mea ... CMOS-logic

The later is nice because it has two LEDs, one for high one for low, which makes it possible to observe what a PWM signal is doing.

What I found useful was to add a counter to such a logic probe circuit. Then you have 4 or 8 or more LEDs counting up in binary. With that even a high frequency input will show as a visible flashing of LEDs at the high end of the counter chain. One can start to estimate frequency.

I bet that with a bit of tenacity one could get a useful old tube scope for about the price of a Pi. For example this one: https://www.ebay.com/itm/HITACHI-V212-2 ... SwSBhbr78A

CRT scopes may be frowned upon as old fashioned and slow but they do have advantages over the new digital stuff.

LTolledo
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Re: "Unfortunately, I do not have a scope, nor does anybody I know."

Sat Oct 06, 2018 11:13 am

currently trying to find latest DIY circuit for the logic probe, capable of detecting Low-0, tri-state 3.3v, tri-state 5v, Hi-3.3v and Hi 5v, powered by 3v only.
tri-states are usually useful for checking data buffer status (well for low frequency digital circuits perhaps)

a 4-bit binary counter would be a welcome addition to that circuit.
"Don't come to me with 'issues' for I don't know how to deal with those
Come to me with 'problems' and I'll help you find solutions"

Some people be like:
"Help me! Am drowning! But dont you dare touch me nor come near me!"

MarkTF
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Re: "Unfortunately, I do not have a scope, nor does anybody I know."

Mon Oct 08, 2018 3:32 am

drgeoff wrote:
Fri Oct 05, 2018 11:12 am
For logic capture the £5 Salae and USBee clones on ebay are a useful addition to your toolbox.
And they can be run with SigRok software on a RaspberryPi.

https://sigrok.org/

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