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Forum Index : Microcontroller and PC projects : DSO's - 2Ch vs 4Ch....
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9610 |
Hi all.  Now, I know what you are ALL probably saying at this point: "Buy nothing but 4Ch!" But I am not convinced. To me, it seems that the only really useful benefit of having a 4Ch DSO, is so that you can capture full SPI. For everything else, single or 2Ch seems to be perfectly adequate, and 2Ch DSO's are HUNDREDS OF BUCKS cheaper then the same type in 4Ch. To me, just for the happiness factor of being able to capture full SPI data, the extra cash is not really justified. But people keep on INSISTING that 4Ch is the only way to go, so I would like the members to give me some examples of where a 4Ch DSO is the way to go WITHOUT needing to show SPI stuff. Even with a 2Ch, you can still sample MISO and MOSI, which are the important lines. CS can effectively be ignored, cos you KNOW it will be low when SPI is happening, and the SPI clock should always be constant, and if you really wanted to measure it, you could do that on a 2Ch DSO just to check it was correct. Thanks. Smoke makes things work. When the smoke gets out, it stops! |
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CaptainBoing Guru  Joined: 07/09/2016 Location: United KingdomPosts: 2170 |
4Ch is nice but I have only *needed* 2+ once or twice and always managed to work around. Personally I wouldn't even look at my scope for the sort of stuff you mention above - I love my 8 channel saleae. I only use it now and then but the bugs fall hard n fast when that boy comes out. personally, if you can afford, go 4, if you'd rather the $$$ in your pocket then go 2... it's a personal thing with no fixed answer (guess which way I went) h Edited 2020-10-27 21:46 by CaptainBoing |
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| Volhout Guru Joined: 05/03/2018 Location: NetherlandsPosts: 5089 |
Hi Grogster, Depends on the trigger channel. If you have a 2 channel scope that has the possibility to view the external trigger channel (as if it where a 3'rd channel, maybe with lower specification), I would settle for the 2 channel. 80% of the scope work, you can cover with a single channel, but in the occasions where you need more, I think 2 is not enough. In my work I often see a situation where I want to look at 2 signals (i.e. I2C) in relation to a event (trigger). In that case you do want to see the event, and the 2 channels. Similar for a symmetrical signal like USB, and a trigger. If the 2 channel does not have a trigger viewer, then I suggest you buy the 4 channel. Volhout Or you can look at a 2 channel with 8 digital "logic analyzer" inputs. May be cheaper than a full 4 channel. Rarely you want to see full analog resolution on all channels. Saleae is great, 100%, slight negative: it lacks a trigger output so you can combine it (sync it) with a scope. Edited 2020-10-27 22:07 by Volhout PicomiteVGA PETSCII ROBOTS |
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| robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2442 |
[edit: while i was writing the below CaptainBoing and Volhout posted their messages. please excuse any duplication in my post] 1. monitoring the current consumption of each phase on a 3-phase motor when started with a soft-starter. yes, i have done this (quite some years back), using the outputs of three current transformers. the scope was a 4-channel low-end agilent. the 4th channel monitored the bypass relay signal. 2. any application where you'd like to record current consumption, supply voltage, and some other signal. very handy when you suspect that a device is briefly pulling enough current to cause a voltage regulator to limit. 3. check coil currents for each of the four buzz-boxes on a model-T ford. the model-T had the most peculiar ignition system: 4 coils with built-in vibrators, and a 'distributor' on the LT side. i was doing this a couple of months ago for a friend. generally, you can do almost anything using just a 2-channel scope, if you can synchronize to some starting pulse or signal in order to align/overlay captures from different points in a circuit using multiple runs. but setting this up takes extra time, and it doesn't take too many jobs where you can save that time (in a commercial environment) for the extra cost to be covered. you can also get by with much less memory, but that is another story! more fundamental differences: A. a 2-channel scope will generally also have a separate trigger input, whereas a 4-channel scope may (as in the case of siglent SDS1104X-E) lack this separate trigger input. in some usage examples the separate trigger input of a 2-channel scope may mitigate the lack of more channels. B. within the same family there may be other feature differences. for example, the SDS1104X-E can be controlled (remotely) from a web browser, supports a wifi dongle, and can preform bode-plotting when connected to a siglent AWG. whereas the SDS-1202X-E lacks these feature. so when comparing 2- and 4-channel scopes from the same family double check that the 2-channel version doesn't have anything else missing. cheers, rob :-) Edited 2020-10-27 22:34 by robert.rozee |
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vegipete Guru Joined: 29/01/2013 Location: CanadaPosts: 1132 |
I get by fine with a 2 channel scope and a Saleae (clone.) The scope lets me see analog details - rise time, actual voltage levels, that sort of stuff. The logic analyzer shows me groups of digital signals. The groups part is key. The Saleae software is good, Sigrok Pulseview is even better for understanding and decoding those groups of signals. (Sigrok s/w understood PS/2, Saleae did not.) For example, my recent dev work on a CMM2 mouse/joystick interface benefited from both devices. The logic analyser showed me deciphered I2C signals (Are you going to remember what a start, stop and clock stretch signal looks like?) and PS/2 mouse transactions concurrently. And the decoders show the actual data bytes that they have decoded. Meanwhile, the scope was showing me the voltage rise time of a capacitor being charged by a joystick pot. A single scope channel has been plenty for so long that I have actually managed to misplace one scope lead. Annoying when 2 would be easier, but survivable. Now for portability, a 2 analog + 8 digital channel scope might be king, _if_ the decoders are comprehensive. Visit Vegipete's *Mite Library for cool programs. |
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Sasquatch Guru Joined: 08/05/2020 Location: United StatesPosts: 377 |
I have several 2Ch 'scopes. I can't ever remember thinking that I needed a 4Ch. It will depend on what you will use it for. From my perspective, you would be better off using the extra money for a logic analyzer as others have suggested. -Carl |
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| CaptainBoing Guru Joined: 07/09/2016 Location: United KingdomPosts: 2170 |
+1 Edited 2020-10-28 03:20 by CaptainBoing |
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TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6283 |
I usually reach for the 2 channel TDS220 Tektronix. 20+ years old. I do have an open-bench logic analyzer and a Bitscope 2 analogue/ 8 digital. Both were cheap and do the job. If I would only use them more often to keep familiar with the process. Jim VK7JH MMedit |
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NPHighview Senior Member  Joined: 02/09/2020 Location: United StatesPosts: 203 |
I bought a 2-channel Tektronix DSO a few years ago ($100 through Craig's List here in southern California), thinking that I'd use it for debugging Arduino and now CMM2 interfacing, but have used it almost never. I loaned it to a local high school physics teacher, who returned it a month or so ago, and it's been sitting on a shelf ever since. The seller said "I can't get the trace to be horizontal or to focus." After I got it home, I found the Horizontal Trace / Focus knob while it warmed up, and turned it. Voila! The local universities (UCLA, USC, CalTech, etc.) and industries have flooded the surplus market hereabouts with these beautiful old CRT-based Tek and H-P scopes as they've rushed to convert to digital, much more portable devices. - Steve "NPHighview" Johnson Live in the Future. It's Just Starting Now! |
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mikeb Senior Member Joined: 10/04/2016 Location: AustraliaPosts: 174 |
Hi Grogs, My Saleae Logic Analyser is my goto for this sort of thing. You can apply many different inbuilt Protocol analysers to enable debugging. I have a Rigol DS1104 DSO and have rarely used more than 2 channels. I think the Logic Analyser is well worth the investment. Particularly for ease of setup and use.  Regards, Mike B. There are 10 kinds of people in the world. Those that understand binary and those that don't. |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9610 |
Hi all. Lots of replies - thanks. Yes, I DO have a GENUINE 8Ch Saelie logic unit, and it is invaluable for logic decoding, so I am not really after a DSO purely as a logic decoder, but I note that many people use theirs for that - perhaps cos they don't have a dedicated logic analyser? Probably. The Saelie Logic 8Ch is a beautiful bit of kit, and it has helped me lots when I had some odd things going on. I remember one instance when it allowed me to identify a non-printable character in a UART data stream, which was the cause of the data packet not being the length I expected it to be. Once I knew that, I could code-around the issue by reading a-byte-at-a-time from the buffer and ignoring that byte. So, I have a logic analyser thing, I am mainly just wanting a DSO for other scope-stuff, that does not fall into actually decoding various data formats. Although, I note that the Siglent include protocol decoding as standard, whereas the likes of the Rigol's want you to pay a couple of hundred bucks more to add that feature, so there is that. I mentioned SPI in my OP, as I see that is ONE major reason people give for getting a 4Ch DSO - you can then use it to examine full SPI, but to me, that really was a non-issue as I have the Saelie Logic if I needed to do that. Sorry for not mentioning that in the OP - it was late, and I was sleepy. I had spent the evening watching gawd-only knows how many videos on YT on various DSO's. Currently looking VERY closely at the Siglent SDS1202X-E 2Ch with Ext Trig, 200MHz, 1Gs which is at a pretty sweet spot at the moment from a NZ Supplier for $730(US$488) in our New Zealand money. Dave over at EEVblog seemed to like it and gave it a good review. Smoke makes things work. When the smoke gets out, it stops! |
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| CaptainBoing Guru Joined: 07/09/2016 Location: United KingdomPosts: 2170 |
yes and yes!. The genuine part not only is superior to clones, it also bolsters a company producing a quality product for not many $$$ (besides feeling reassuringly heavy and substantial in the hand). I "obtained"  a chinese clone that (if memory serves) turned out to be not much more than a microcontroller that lied to the software... how on earth can that go down to the 10nS of the genuine item? Crappy test gear = crappy test results.my "war story" concerns a one second tick produced by dividing down a 12.288MHz TCXO of +/- 100ppb... a bug in some dodgy logic design by yours truly was shortening each second by 8.2uS - I would never have found that with a scope and I had stared at the logic in the code and schematic for days... it fell within the hour when Saleae put his boots on. I printed up a "test jig" for PCBs with "cranes" that reach over onto sections each with a pogo pin on the end. It makes getting the test hooks a breeze to connect - the one thing that is always tricky and more-so when you have 5,6 or even 8 of the simultaneous connections to make. I'll see if I can find it on thingiverse and post back as an aside. Edit: found it he uses accupuncture needles but I used pogo pins Edited 2020-10-28 20:05 by CaptainBoing |
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