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anachranerd
03-05-2009, 07:42 PM
Anybody have recommendations on a good affordable o-scope for automotive work?

klapa
12-06-2009, 09:59 PM
As a design engineer who uses O'scopes on a daily basis - I can tell you that "good and affordable" don't exist for oscilloscopes.

Automotive applications have even greater demands - if you are looking to monitor ignition directly you need high voltage channels.

Even without direct monitoring of ignition - you need a scope with a fast rise time - which means you need a high-bandwidth scope - and such is far from "affordable" for an individual.

Best bet would be to find something on eBay or such from some outfit going out of business - still - unless this is for business and you can get some payback - it might be far from "affordable".

anachranerd
12-06-2009, 11:37 PM
So we are talking 800+ for a good one maybe?

LIke this-
http://cgi.ebay.com/ebaymotors/Automotive-Labscope-Easy-To-Use-2-Channel-Oscilloscop_W0QQcmdZViewItemQQhashZitem1c06f509f6Q QitemZ120375806454QQptZMotorsQ5fAutomotiveQ5fTools

joe's gt
12-07-2009, 12:13 AM
Sh*ts expensive dude. What do you need it for?

klapa
12-07-2009, 02:08 AM
That scope looks allot like a re-packaged "scopemeter" similar to those made by Fluke - a well known test equipment company. Maybe two channels would be Okay - and maybe thesed two channels are truly simultaneously sampled channels or have a sample rate great enough to render a true view of what s going on - or maybe that is just an $800 boat anchor.

Just remember - at eBay - by the time you get the goods - the warranty has expired~

For automotive ignition and ECU analysis - I would think you would need at least 4 channels - and preferably 8 channels capable of simultaneous sampling - to monitor all the cylinders on any car you would reasonably come across.

The kinds of scopes I use on a daily basis are over the $10K range - with some up in the $30K range - yet I would think a good "garage shop" quality automotive analyzer would come in around the $10K range for a new one - and perhaps as low as $2K for something sold at auction.

The question above was well put - what do you need to do with it?

If you are planning to repair/modify ECU's then you would certainly need such a scope - if you only want to tune your car or something like that there are much cheaper shortcuts.

I wold expect to spend at least $2K and probably closer to $10K for something that would be "business quality" for automotive diagnosis.

anachranerd
12-07-2009, 05:51 AM
Well, my immediate concern is why this ford escort isnt getting any spark. Ive got 12v going to the coil, but im wanting to see if the trigger wire is getting anything. Digital MM isnt really up to snuff to see if the trigger is doing anything.

In general, ive done some basic programming with a 68 hc11 chip for experimental/hobby ecu im working on. I need a scope to further examine whats going in and out. but havent had a chance to touch it lately.

Im a novice with electronics, but im getting deeper and deeper into it so i'm going to need one.

10k$ scope is beyond me right now, give me a year or two and maybe.

anachranerd
12-07-2009, 05:53 AM
oh and an o scope would help read these hall sensors

klapa
12-07-2009, 07:06 AM
I think you are on the right track there and share your enthusiasm for electronics - that's how I pay my rent.

If you need to look at the trigger for the coil then a data acquisition system would do that job well enough on the low-voltage side - and be more usable for other projects down the line.

My suggestion would be to look around for USB based A/D converters - these might be available for as little as $100 and give you a good idea as to what is going on in such a scenario while not costing so much. National Instruments is the "high end" dealer for such, but there are now many pretty good quality PC based data acquisition systems that are cheaper than a multimeter - you just need to be careful to scale your input voltage to the requirements of the device - something easily done with a cheap resistive voltage divider. You also need to be careful to choose a system that has a sample rate fast enough to capture the events you wish to see.

After all - in this case you really don't need the accuracy so much as the "go/no-go" picture of what is happening. A picture IS worth a thousand words and that is what a scope is good for.

If I could help you more - just ask. You are all the way up in Mizzou - so not close enough to just come here and just use my lab.

klapa
12-07-2009, 07:21 AM
Of Course - I just happen to have here at home an extra scope - a LeCroy 9400A 175 MHz vertical bandwidth digitizing two channel scope with dual independent delayed time base capture and 2048 byte samples memory for each channel.

I also have a 1992 Celica STX that "purrs like a kitten"!

If YOU might happen to have something like - say - a pre-1997 Celica GT that does not smoke - maybe we could talk some real Turkey here.

Anyway - I have information any day - and that is always free for the people here on this board.

anachranerd
12-07-2009, 07:14 PM
klapa- thanks for the offer, no spare GT's laying around :(. I found a nice used one of those on ebay for ~700...ill have to look into it.

Just out of curiosity, how would you make your divider for measuring a 12V trigger line? Would I need to divide a low voltage like that?

klapa
12-08-2009, 01:18 AM
anachranerd,

I really like that LeCroy scope - for one that I have used it for many years and for two that it is one of the few scopes that you can expand BOTH horizontal and vertical on a captured waveform - that meaning you can set you horizontal to acquire many transitions in single trigger mode - then expand that out with a very fine time step to pan through the waveform and make measurements, analyze the data, etc.

If you do indeed plan to make electronics an avocation, then that would be a very good first scope for your own personal lab - yet if you are in a money bind or something and just need to fix your car, there might be a better temporary solution to use troubleshooting the problem. This would be to add a simple RC low-pass filter and measure the voltage with a DMM. This would just be a resistor in series terminated by a capacitor to ground. Measure the voltage at the junction of the resistor and capacitor. If you have four circuits, then you could simply compare the voltage readings to see if something is abnormal about one coil or the other - or the drive to each coil (ECU driver). I would start with a filter setup for high frequency - something like 200 ohm into a 100 pF capacitor to ground.

As for your question - you would not need any divider to measure the 12 VDC coil drive pulses - as nearly all scopes are max 600V Peak input before damage - yet you WOULD need a divider to measure the secondary side of the coil - which would be in the 20-40 kV range for modern electronic ignition systems.

In the case of the high voltage - unless you really need to know the actual voltage or diagnose spark plugs - simply "hovering" your scope probe near the plug wire will show the waveform - through the "antenna effect". The further away you hover he probe, the lower the amplitude of your trace. So here you wouldn't get an actual measurement of the voltage - but you would get an actual picture of the pulse waveforms and the relative seperation in time between the cylinders. Another old trick there is to wind a few turns of wire around each plug wire to create a little transfomer - with the HV plug wire as the "primary" and this little winding as the "secondary" - and then to connect each side of the scope probe (ground and tip) to each side of this little winding you have made. This is the "poor man's" inductive pickup. Note though that in this case the waveform will be slightly distrorted due to the added inductance - as determined by the number or turns added.

anachranerd
12-21-2009, 10:43 PM
I ended up getting this guy new for 200$. Not too bad, one drawback is it is only one channel.

http://www.vellemanusa.com/us/enu/product/view/?id=351409

Question- my crank sensor is a Variable Reluctor type. To measure it, im assuming ill have to set my scope to AC, and should I hook the probe to one wire, and the ground clamp to the other wire? The crank sensor has two wires on it. Or should I hook one clamp to a signal wire and the ground clamp to chassis ground?

I wish this thing had more memory on it.

Apologize for the severely nooby questions, Im still very new to this electronics game :) But I LOVE it...

anachranerd
12-21-2009, 10:44 PM
Also, last night I hooked the probe to one wire on the crank, the ground clamp to the other. With the ignition ON, but not Cranking, it showed a waveform of about 25mV amplitude before cranking. Im wondering what was causing that.

klapa
12-23-2009, 04:58 PM
I ended up getting this guy new for 200$. Not too bad, one drawback is it is only one channel.

http://www.vellemanusa.com/us/enu/product/view/?id=351409

Question- my crank sensor is a Variable Reluctor type. To measure it, im assuming ill have to set my scope to AC, and should I hook the probe to one wire, and the ground clamp to the other wire? The crank sensor has two wires on it. Or should I hook one clamp to a signal wire and the ground clamp to chassis ground?



The "variable reluctance" type of sensor is essentially a transformer that works by having a large chunk of iron attached to the crank pass by in close proximity changing the core properties of the transformer. You would expect to see a low amplitude (millivolts) AC waveform at the output leads. You should be able to monitor the output by just placing your probe tip and ground across it - as the car's ground would not be connected in any way to the scope (power) ground. It is difficult to make much "sense" out of the waveform, as usually the receiver has a filter before the signal is transmitted to the control unit (ECU).

Another (better) way to monitor that signal would be to rig up an op-amp in differential input configuration and look at the signal at the single-ended output to ground.



I wish this thing had more memory on it.


One channel can be enough so long as you set up nearly identical triggering you can make measurements between different cylinders and signals. As an example, if you set up your trigger to be the firing signal through the distributor and then do not change the trigger level, you could check each cylinder waveform and save it each time then compare them all against each other.

That scope has two memories - so I suppose that means you can store two waveforms - yet it also has an RS-232 interface - thus you should be able to write a simple program to download the data to a PC and look at your waveforms in Excel or something like that.

Looks pretty good for only $200 - especially good as it has DMM readout as well. 12MHz vertical bandwidth should be good enough for most general purpose stuff.

klapa
12-23-2009, 05:04 PM
Also, last night I hooked the probe to one wire on the crank, the ground clamp to the other. With the ignition ON, but not Cranking, it showed a waveform of about 25mV amplitude before cranking. Im wondering what was causing that.

That type of sensor is "excited" by the driver/receiver circuit with an AC signal. The AC signal amplitude changes when the piece of iron passes by the core. The receiver circuit filters the signal such that a pulse train or varying DC voltage is developed from it.

anachranerd
12-23-2009, 07:31 PM
Hey Klapa,

Thanks for your time dude. Appreciate all the info. Though you are still WAY over my head with stuff. Im reading about op amps and things like that, but I have no idea how to build them yet.

The waveform i got off the crank sensor looked exactly as it should according the edis documents from megasquirt.

http://www.megamanual.com/ms2/EDIS.htm

Here is what i captured from the crank sensor from the sensor wiring about an inch from the actual sensor. I had to strip the wires and probe them, the way the crank sensor is placed there I couldn't just probe at the pins of the sensor itself.

http://img130.imageshack.us/img130/7186/crank1.th.png (http://img130.imageshack.us/i/crank1.png/)

joe's gt
12-23-2009, 08:44 PM
Wut do you need to know about op-amps? my engineering curriculum went over them a little bit, so I might be able to help you out. Hopefully there is an EE on this site that could help you out more tho.

anachranerd
12-23-2009, 09:43 PM
Nothing specifically about op-amps per se--just saying that I am very much a novice in this electronics stuff so a lot of what he says flies right over my head

joe's gt
12-24-2009, 03:18 AM
yeah, what he is saying is flying over mine too. Then again, I have very little experience with oscilloscopes. Op-amps are difficult to get the hang of. There are inverting, non-inverting, difference, etc. Then there are in-amps as well. Just look for the already simplified equations, cuz trying to calculate them yourself is a pain.

klapa
12-26-2009, 05:46 PM
Didn't mean to get too technical - the difference between a single-ended and truly differential signal is that the differential signal has voltage on both the + and - lead and the - side is not connected to the power supply common (ground).

Usually such a signal has a "difference" amp as a receiver. The reason for using such a signal is that it is very immune to noise injected from outside sources, as such noise would be introduced on each + and - line, and would be eliminated by the difference amplifier receiver. Thus a millivolt level signal can be routed near sigh level signals and not be effected by them.

When you probe such a signal with a "single ended" receiver - such as a scope input with one side "common" - you will see only one half the signal amplitude that you would see at the output of the difference amplifier. You would also see noise that you would not see with a true differential mode probe.

Op-Amps can be difficult for a novice if you attempt to build up a circuit using all individual resistors and capacitors - but these days you can get such on a single chip - a good "poor-mans" differential probe is such an amp called an "instrumentation amp" - all you need do is add a single external resistor to set the gain - usually a potentiometer (variable resistor) so you can change the gain for different situations.

Here is such a chip:

http://www.analog.com/en/amplifiers-and-comparators/instrumentation-amplifiers/ad8220/products/product.html

Such a probe can be very handy to look at differential signals - and is very cheap to implement.

karl
04-13-2010, 04:19 PM
came across this and thuoght it might be useful info for this thread:

http://www.sparkfun.com/commerce/product_info.php?products_id=9625

http://static.sparkfun.com/images/products/09625-04_i_ma.jpg

$99 handheld scope. might work really well for automotive stuff.