oscilloscope suggestions?

JohnC

Missing a few cylinders
#2
I have one of the USB 'scopes similar to your 2nd link. It's noisier than a quality scope, but it gets the job done for 10x less. Unless you're chasing millivolt signals, it'll probably work for you - anything above a volt or two is fine, even if there's a fair amount of ripple & noise that comes in too.
 

Alan Watkins

Lifetime Premier Supporter
#3
I have one of the USB 'scopes similar to your 2nd link. It's noisier than a quality scope.
Just curious: is the noise typical random 1/f noise or mains/hum-related? IOW does it help to use it with a laptop that is under battery power?

As an overall comment, strictly for garage use I'd probably first look at hand-held, battery-powered LCD display scopes just because cables (USB and/or power) are pretty inconvenient around cars, as are laptops and normal-sized scopes since you have to put them somewhere and a lot of times a fender, etc., doesn't really work. One fall to the concrete floor and....

So looking around Amazon, to my amazement I see some for less than $100. And also a Velleman unit for ~$140:

[ame="http://www.amazon.com/VELLEMAN-HPS140I-HANDHELD-POCKET-included/dp/B004QYOXQS/ref=sr_1_11?s=industrial&ie=UTF8&qid=1372036407&sr=1-11"]VELLEMAN HPS140I HANDHELD POCKET SCOPE 40MS/s (probe included): Amazon.com: Industrial & Scientific[/ame]


And these two that for the
 
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#4
John

one of the main considerations with scopes it the sampling speed, it is kind of a circular debate, you need to know the speed of the thing you are trying to see before you can specify the scope that will see it. I run an electronics company and we have both bench and PC based scopes. The PC scope are OK for slow speed signals, the UI is usually crap (they generally try to replicate in software the look of an actual scope, which does not work, either aesthetically or functionally, my opinion).

I recently took a punt on a new scope from china, Owon, £250, about $375, it is not bad.

How much you want to spend, what likely speed is the signal, how many channels you need, would recommend generally getting 2 channels, plus a trigger input.

let me know if you want me to look at some ebay stuff you have highlighted?

Keith

OWON SDS7102V 100Mhz Digital Oscilloscope 1G/s large 8" LCD LAN VGA UK Shipping | eBay

It works quite well, 100MHz.

The 2 channel Hantek one you showed, looks fine!
 
#5
I recently got an old school analogue one for under £50 off ebay. It's got dual inputs on the front, plus another on the rear. I'm hoping it'll do all I need for when I'm building / setting up the megasquirt and sensors / outputs etc.
 

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#6
James, what do you have to do to set-up megasquirt,.... just out of interest, are you using the engine timing pulse as a trigger then adjusting the time between TDC or firing and the injectors opening time and open duration? K
 
#7
Hi Keith

I'll be honest with you - I have no idea! I'm still researching how to do a standalone system, and leaning about fuel injection, ignition, cop, injectors etc... Lots of reading through books and also on MegaSquirt Engine Management Systems

It looks like an oscilloscope is useful for things like working out the dwell time on coils and checking the shape of the crank / cam signals etc.
 
#8
James,

I have my engine running on a megasquirt II, although I have been running into some issues. If you look at this thread you can see the rundown on what my issue is.

I think you will find that setting up the megasquirt is not as complicated as it might seem. A lot of that stuff you're reading is most likely theory, and in practice, its a lot easier to do.

After pulling off the intake more times than I can count now, I'm pretty certain that the issue I'm having is being caused from a electrical problem. I'm pretty confident of this because, as far back as I can remember, I don't think this car has ever run right and its running pretty much the same way it always has despite a whole new engine and ECU. The only thing that hasn't changed is the old wiring... I'm hoping that the O-scope can help me find the issue, though, i don't know how to run one at all!
 
#9
Hi John

Glad to hear setting up the MS is easier than the theory! Thanks!

Just had a look through your other thread... Have you tried posting your MSQ from the MS onto the MegaSquirt Engine Management Systems forum and asking for help there? If you're suspecting something electrical, someone might be able to see if anything looks odd in the way the MS is set up?
 
#10
Yeah, i posted my issue on there with the MSQ a while ago, no one could help. Those guys are good at helping you get your engine running, and tuning issues sorted out, but its a whole different world when it comes to chasing down electrical gremlins that are most likely outside of the MS unit.
 
#11
Ah, OK. Thought it was worth a shot. Good luck finding the issue. I'm sure you'll be glad when you've finally got to the bottom of it. Can't be far away now...
 

JohnC

Missing a few cylinders
#12
Just curious: is the noise typical random 1/f noise or mains/hum-related? IOW does it help to use it with a laptop that is under battery power?
Alan, it does seem to be quieter when running on battery power than mains. Someone mentioned using the scope for checking dwell, so here's a dwell waveform as an example. This is from my 550 Maranello's ignition before I converted it to COP:

 
#13
I think the Hantek one I listed above might be the one to get. I saw some reviews on it and most of the negative things about it seemed very esoteric. The one major problem with it was it locked up a lot for the reviewer. I think he might have been using a very early one since the review was from 2011. I went to Hantek's site to see if they had any newer firmware and I found that they have a version that was released a few months ago.
 
#15
Can I put the scope right on the high tension leads? I'm really not sure how you hook these things up.

Do I need to get a 100x prob or something?
 
#16
John, generally NO (sorry for shouting), the best way is to wrap a piece of aluminium kitchen foil around the HT lead, then clip to that. I'll mock one up and post a pic in a while. Connect the earth croc clip to the earth/ground of the car. Keith
 
#17
John, here's a mock-up with a copper foil, try this and see if you get a good pulse, try the probe on x10 first and see what you get, then move to x1. You can get quite a thump off the leads when she's running, so keep the HT lead on the plug. K
 

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#19
John, no you should not get much pick-up from the others, the capacitive coupling (which is what the foil is to the wire) is quite tight, whereas the coupling to the other leads via the air is loose, just wrap the foil in a position where there are no adjacent HT leads. Are you looking at the HT (spark) to get a timing reference? K
 
#20
I want to compare my good cylinders to my 'bad' ones. See if there's missing and make sure the ignition system is simply healthy.

I also want to see a lot of low voltage stuff as well. What the voltage looks like going into my ECU, VR sensor signal and so on...
 
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