relay bleed through cadi trunk pop dmm

By the way, how is that ebay "arm dso portable mini" ?

Seem like it might be an interesting little thing to play around with-  have you found it to be actually useful?

Rather low sampling rate as DSO's go, but it looks like it would be handy to have around, being so portable.  Battery life decent?

So far battery is excellent, and it works great for reading RCA output clipping, but that's about all I've done with it. So many fancy settings I'm not familiar with, but I'm sure as my buddy is going through EE Schooling he'll want to fill me in on all how all those type of measurements function. Is there a more detailed picture of that diagram? A few characters are a bit fuzzy. Keep on rockin!

Sounds good, I might get one to play with-

Yeah, the jpg was low resolution to meet the limitations of the upload sizes here; I'll get a better one to you when I get the chance.  You don't really need the details like the pin numbers if you look up the part's datasheet though-

http://www.mouser.com has the datasheet, the other stuff should be common items you could probably pick up at the local supermarket-

"The 2.2M resistor will put a slight current on the input, but it's minimal enough not to worry about." -dualsport Based on this thought, and since these diagrams have blown my mind, can you attempt to explain what types of currents or voltages would potentially cause damage to even the most fragile circuits in a vehicle? --------- One of my former superiors said "computer safe test lights can still potentially cause damage to modern vehicle electronics". Is there a way to prove him wrong about my Snap-On (GREEN/ red) LED light? Could I use my DMM to "test the test light" and see if it passes the test? Hehe... I used it for years without a problem, then the "no test light rule" came into effect. Know what I mean? I miss my dang light! :( I will try again shortly to comprehend that diagram and what it would allow me to do, unless I find out my computer safe light actually is computer safe... Yall have been great - Thanks again!

I don't know how the Snap-On test light is designed, so I couldn't really say what it might do.  If it's an expensive item, as I would guess it is, I'd assume it's more sophisticated than a simple LED connection that runs off the input signal. 

If you take something like a 1M resistor or larger, connect it between your test light input and 12V, and measure the voltage with your DMM, you should see 12V.  Then if you connect the resistor between the test light and ground, you should see 0V.  That indicates your test light isn't putting any appreciable current out to the signal under test.  If, however, the test light overrides the pullup and goes to some voltage regardless of how you connect your pullup, it's putting a load onto the signal, and it might be an issue, depending on how much it is.  You could try with progressively lower resistor values until you see the voltage change, if you were interested in just how much of a load it is.

6 microamps is unlikely to cause damage, if automotive electronics were sensitive enough to be damaged by that, we'd have to be careful about sneezing around them-  

I've always heard the issue with test lights was only with the incandescent style (the old ones).  They pull a decent amount of current and they can set air bags off.  I've never heard of anyone damaging a computer with a test light but I have heard of multiple people setting off air bags with them.

I've personally never use a test light at all - I rather use a cheap Craftsman meter with "bed of nails" alligator clips.  When I'm looking for a quick pulse I'll pull out my fluke, but for "everyday" use the Fluke is overkill and not worth losing / damaging.  I'm guessing (or hoping anyway) I am not the only one that has actually ran over a multimeter in a bay....   :)

Kevin Pierson

KPierson wrote: I'm guessing (or hoping anyway) I am not the only one that has actually ran over a multimeter in a bay....     :)

You got me there- never did that, but did you ever drop a DMM off the back of a motorcycle when the luggage lid flew open without your knowing, and continuing to ride merrily along for miles and scattering all sorts of goodies on the highway as they flew out with every bump?

Not quite running over a meter, but I did witness somebody back a car out of the bay with a fluorescent drop light ran through the door.  He said he knew something happened when the car suddenly got darker inside.

I know I'm going to be skinned alive but yes, it's an incandescent bulb test light. Having said that, I've been in this business since the early 70s and you learn common sense and evolve or else. Discretionary use is how I would describe it. Forget computers, air bag wiring and CAN signalling lines are the problems. Never seen permanent damage from working on processors, come to think of it I always thought the stories of air bags going off whilst working on cars was an urban legend. And yes even with fluorescent Snap-On tool handles, I still leave the damn things under seats. What next, RFID chips in the handles?