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Need help with a wiring challenge

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tomj View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tomj Quote  Post ReplyReply Direct Link To This Post Posted: Oct/22/2019 at 10:57pm
yeah, but watch for what a signal MEANS. the two stepper motor lines will, at best, flicker on when there's any change. "change" is constant however, and won't in itself indicate anything meaningful about engine state.

i'm dubious about your "resistor to relay to LED". you can't just hang a relay of any old thing. you have to have some idea of what a given signal drives and how much current you can "steal" from it. assume the worst -- OEMs cut things down to the thinnest margins they can get away with consistent with reliability. that's smart design. hang a relay on a sensor and you will (will) ruin that sensor reading. and could actually do harm. (relays are inductive loads.)

an LED with a resistor to limit current would probably be safe for most signals. not O2 sensors though, those absolutely require an opamp micro-amp analog buffer, they output a very weak bi-polar (plus and minus) signal.

i suggest making a schematic drawing of each signal and what you intend to connect to it. building electronics means makign lots of drawings.

1960 Rambler Super two-door wagon, OHV auto
1961 Roadster American, 195.6 OHV, T5
http://www.ramblerLore.com

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zeebo76 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote zeebo76 Quote  Post ReplyReply Direct Link To This Post Posted: Oct/22/2019 at 11:44pm
This is all going to hang off of the diagnostic ports.  Those are specific, separate wires intended to be read off of, and in addition the relays I'm using are very small and use very, very small load.  They can sustain a 25mA current running through them, which is barely any more than an LED diode can carry, so I really doubt that setting up the box will throw off any sensors since I'm using a combination of very thin wire, resistors, and very delicate relays intended for electronic controls.  These are not automotive relays - they are relays that are intended for uses like motherboards, graphics cards, things like that.

As for the O2 sensor, all I'm wanting to do is tap into it to read exactly what voltage is being sent.  Others have done it with no issues, so I don't foresee any issues on my end as long as I follow their leads.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bigbad69 Quote  Post ReplyReply Direct Link To This Post Posted: Oct/23/2019 at 7:59am
If your box is intended to sit on the dash, I suggest not using green LEDs. They don't get very bright and sunlight readability could be an issue. Blue LEDs can be made very bright.

It might be an idea to make the LEds dimmable for varying light conditions.
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zeebo76 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote zeebo76 Quote  Post ReplyReply Direct Link To This Post Posted: Oct/23/2019 at 2:16pm
That's true, bigbad...  Maybe I'll make a sunshade for the box?  I'd prefer red/green for the "bad/good" connotation behind the colors, but if green doesn't work out I have a box of 1000 LEDs in green, white, red, blue, and yellow.  If I can't make the green work I have some other options to try out.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote zeebo76 Quote  Post ReplyReply Direct Link To This Post Posted: Oct/23/2019 at 5:56pm
To clarify some things about the purpose of this device:

It has multiple purposes.  I want to both be able to easily tell what's happening if the car starts running wrong, and be able to tell if any of the sensors are having errors at a glance.  I would like all of this information available to me in the driver's seat because I want to be able to say "Oh, well, I just stumbled, and this sensor should have been on.  It's on now, and I'm not stumbling anymore, so I should start looking at that sensor to see what's going wrong."  Even if the car isn't running badly, knowing that a sensor is malfunctioning allows me the time to inspect/repair/replace the part so that it doesn't BECOME a problem.

On the 258's with all the emissions controls, it is pretty essential that everything works as it should, for both drivability, emissions, and gas milage's sake.  If I were to deny myself the ability to easily notice when something is wrong with any possible sensor, I might as well nutter the car and be done with it - as this device should be as comprehensive as possible to make repairs more expedient.  Leaving something out when I could just as easily build it in and have the information would be foolish, in my opinion.

This is likely a rather long response to your remarks, tom - but, I just wanted to explain that the intent of this project is not just to cover the most important items on the car, it's to cover everything I can, so I can catch whatever's happening while it's happening.  And, like I mentioned in a previous post, I'm taking power draw from my components into account.  The relays I'm using aren't much larger than the tip of a pen, and the maximum amperage they can take is not much more than my 3mm LED diodes can, so I'm not worried about drawing too much power from them.  If a technician can plug a multimeter into any one of those ports and run the car without issues, I doubt that a 25mA draw on the same port a multimeter would plug into will cause any issues at all.


Edited by zeebo76 - Oct/23/2019 at 6:03pm
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First_Gear View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote First_Gear Quote  Post ReplyReply Direct Link To This Post Posted: Oct/24/2019 at 12:35am
I work in electronics.. I would NOT use relays. They tend to wear out over time, get hot and draw allot of current. Look to integrated circuits and transistors. Each component has a datasheet that explains how to implement them and they make chips that do just about anything. I could probably design something but you will learn more if you build it yourself.

This is a good starting point with digital logic:



Edited by First_Gear - Oct/24/2019 at 12:42am
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tomj View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tomj Quote  Post ReplyReply Direct Link To This Post Posted: Oct/24/2019 at 10:00pm
First_Gear is totally correct. relays are a bad idea. they are an inductive load, can generate spikes that ruin what's driving them, if that is an electronic circuit. relays are slow. if a signal is rapidly on/off, the relay can't respond.

relays in 2019 are relegated to legacy applications and high power/low cost.

integrated circuits will be superior in every way. some are really easy to use.

have you made a list of what each signal is, i mean electrically? powered solenoids? analog sensors? what's thew signal? 0 to 5V on/off, 0/12V, PWM, or a varying voltage?  each type needs a different input circuit. most are very easy, but you will need to understand to some degree how each signal behaves.

that said, this is a good project to work out electronic interfaces.

1960 Rambler Super two-door wagon, OHV auto
1961 Roadster American, 195.6 OHV, T5
http://www.ramblerLore.com

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