automotive oscilloscopes

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spro
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automotive oscilloscopes

Post by spro » Sun Feb 11, 2018 7:40 am

There was a time when a portable scope designed for engines were the thing. In a torrent of rain, the analog scopes are not the best. I knew that technology would overtake my old stuff. I didn't know how far it would become nor the options available now.
I feel immersed into an ocean of newer possibilities. From what recently seen, inductive pickups require more "front end" and some ways require piercing individual leads HT cables. The old analog stuff worked like a regular oscilloscope and had dependable controls but rain and snow cause many problems.
Something new and hand-held. There are many but I want to see the wave form and interpret that into my brain. The kv relationship is important as the "parade" relationship of one cylinder to another at a certain time or rpm. There have been so many over the years , I don't know where to start with the newer portable ones.
Recommendations here are welcome.

TomB
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Re: automotive oscilloscopes

Post by TomB » Sun Feb 11, 2018 11:09 am

40 years ago I converted a Heathkit standard low quality scope into an Auto scope. I had to change a cap on the sweep rate selection switch to provide a slower sweep rate and I built a pickup for the spark signal. The pickup was easy I took a piece of 1/4" soft copper tube about 3" long, sawed it in half lengthwise then glued each half to a spring clothes pin. I had some high impedance coax and with just a bit of impedance matching components (don't remember what they were but then I was not so time removed from college) soldered to the copper pipe and then to the coax I had a pickup. I had a book about auto scopes and what the signals meant. I clipped close pin pickup over a spark wire and immediately got reasonable images of the plugs spark signal. The images matched what was in the book and I was able to get the old 1200 Fiat roadster running well.

There was nothing particularly weather sensitive about the hookup and the induced voltage in the pickup was so small it had to be amplified by the scope so nothing was dangerous. I would not recommend poking holes in the plug wire insulation as that would seem to be the first step in a shocking event.

spro
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Re: automotive oscilloscopes

Post by spro » Sun Feb 11, 2018 6:27 pm

Thanks for the read, Tom. I want to skip some generations and get a truly portable, battery powered thing. I know there are many "apps" out there which could convert certain laptops or notebooks to this use. Like you said, "inductive" is the key, to me. If I had a smart phone I wouldn't use IT for this but something with a larger screen that could be adapted.

TomB
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Re: automotive oscilloscopes

Post by TomB » Mon Feb 12, 2018 11:43 pm

To bring my old experience up to date as a DYI project one would have to connect the inductive probe to an AD converter in the smart phone, assuming it had an adequate sampling rate and sufficient sensitivity. I know of no way to measure the voltage developed by the sensor other than hooking it up to a scope and reading off the required scale factors. Then with the signal stabilized I would estimate the signal bandwidth by using notch filters. To estimate note that plugs fire at 240Khz rate or with 4 us period. The spark takes about 1% of that period so the frequencies involved would be a minimum of 20 Mhz. To adequately sample the signal will require a sampling rate that is 5 to 10 greater than the base frequency. Therefore the A/D sampling rate would need to be 2 to 4 million samples per sec. I don't know if the A/D converter that is available to a smart phone programmer will support that rate. I expect the A/D convert would expect the input voltage to be similar to an audio mic output. That is a 0 to 1 v range with sampling suitable to audio requirements, less than 40 Khz. Where I expect the voltage in the pickup I described is 0 to 1 mv. So someplace in the chain you would have to include a 1000x amplifier. A servo amp with 1 to 1000 feedback could provide the amplification and since it only a single chip you could put it in the probe.

I probably could put all that together, but I would have to set up a lab and use it to refresh my memory and to set up and verify my current thinking. But it would be way more work than this retired engineer would consider feasible.

As a product development with young and enthusiastic engineers and programmers it would require a lot of funds to design, setup and manufacture. Not sure that sales of such a device could return a profit on that effort given the small demand for such a unit.

spro
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Re: automotive oscilloscopes

Post by spro » Tue Feb 13, 2018 12:08 am

Tom. Thanks for taking the time to explain this.

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ctwo
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Re: automotive oscilloscopes

Post by ctwo » Tue Feb 13, 2018 12:46 am

I cannot speak to the application; however, the general topic of oscilloscope - especially entry level oscilloscope - I am very well familiar with.

Picoscope has equipment geared toward automotive. However...

The Rigol DS1054Z is $350, free shipping, from Tequipment, and I can give you a code for another 6% off. This model is only really appealing if you are willing to go to a website, enter the serial number to get a key code. The scope already comes free (limited time) with all software features enabled, and the generated key code is entered via the front panel or via commands sent over USB or Ethernet. This is expanding bandwidth to 100 MHz. The response is actually ~130 MHz. Note: it does not have any of the automotive protocol decoders, so you would need to use something else to get codes and program the vehicle... It can have all of the GP decoders such as RS-232/UART, I2C and SPI.

Disclaimer: I have this scope fully unlocked and have researched the lower end products for a couple years and this is currently the best option in this class of equipment.

Last edited by ctwo on Tue Feb 13, 2018 1:00 am, edited 1 time in total.
Standards are so important that everyone must have their own...
To measure is to know - Lord Kelvin
Disclaimer: I'm just a guy with a few machines...

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ctwo
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Re: automotive oscilloscopes

Post by ctwo » Tue Feb 13, 2018 12:47 am

Oh, it's NOT water resistant - and that was not my video...
Standards are so important that everyone must have their own...
To measure is to know - Lord Kelvin
Disclaimer: I'm just a guy with a few machines...

spro
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Re: automotive oscilloscopes

Post by spro » Tue Feb 13, 2018 12:52 am

My newest vehicle has OBD II and I have a scanner which works with the auto's ECM. I've replaced a few injectors by that. There is something else going on because there is a "snap" detected by AM reception. I'm not piercing leads to find that. There are two catalytic converters and at least two O2 sensors varying things about. They clean up the emissions and don't throw a code but there is more happening.
I miss reading the 'scope.

spro
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Re: automotive oscilloscopes

Post by spro » Tue Feb 13, 2018 12:59 am

Ctwo . Before I watch the video, thanks! I had looked at the Picos but didn't see the Rigol 1054Z.
Consider it seen and my appreciation at this time. G'nite after watching.

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ctwo
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Re: automotive oscilloscopes

Post by ctwo » Tue Feb 13, 2018 1:01 am

Well, for a quick overview...

Standards are so important that everyone must have their own...
To measure is to know - Lord Kelvin
Disclaimer: I'm just a guy with a few machines...

spro
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Joined: Mon Feb 20, 2006 11:04 pm
Location: mid atlantic

Re: automotive oscilloscopes

Post by spro » Tue Feb 13, 2018 1:15 am

Okay. This is a different thing but now we know.


Okay now ctwo. You're killing me :) I've seen this guy and he is brutal with bad equipment.
Good freakin mornin'

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