0-5VDC analog signal from a WB O2 monitor

Discussion in 'The Projects Forum' started by TheEquineFencer, Aug 12, 2010.

  1. TheEquineFencer

    Thread Starter Active Member

    Apr 20, 2007
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    OK, here's what I have. I'm looking at using a Wide Band O2 sensor that has a 0-5 VDC output. 0V = 10 AFR, 5V=20 AFR Air Fuel Ratio. Voltage output goes from 0v=10 to 0.05V= 10.1, 0.1V= 10.2, 0.15V= 10.3, here's a link to the table to show the range.

    http://www.innovatemotorsports.com/r...ogOutTable.pdf

    What I want to do is use this signal to trigger an alarm when the AFR reaches a preseleted level, too lean. I want to be able to select the level with a digital display, but for now I'd be happy to use a potentiometer and a Fluke meter if I can to select the preset point. I guess what I want to do is be able to select when the 0-5V input rises above a preset point.
    I'm a 50 year old "newbie" to working with electronics, so please bear with me, I'm still learning. I know what I want to do and have reasonable understanding of how componets work. I think what I need is some type of comparator with an way to adjust the input voltage preset point and use a mosfet to trigger the alarm. I was wondering if I could use some type of circuit that uses a LM 3914 Ic? I'm open to ideas.
     
  2. beenthere

    Retired Moderator

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  3. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Actually this isn't a soup up or circuit that in any way hooks up to or modifies the pollution controls, he's just looking for a warning if his air/fuel ratio accidentally goes too lean which could be considered to be a tester. (and an engine saver) Cars don't come with wideband O2 sensors nor will they interface with the computer controls used. Had he asked how to adjust the injector pulse width utilizing one it might be different. He just wants a simple A/F gauge.

    People commonly add something like this to ensure that their existing turbo wastegate is closing or that their actual emissions controls are working properly thus ensuring the engine is operating properly and NOT contributing to pollution. It's a totally self-contained circuit :: +, GND, the sensor and a readout method.

    To beat all he's pretty well already got a solution to his own question, matter of fact there are plenty of kits on the market that already do this with just the LM3914 IC coupled to a dot/bar display. The circuit as well as the calculations for the values would be in the datasheet for that IC. I use the identical circuit (in expanded scale) as a battery voltage level indicator for forklift batteries thus estimating the amount of charge left.
     
    Last edited: Aug 12, 2010
  4. SgtWookie

    Expert

    Jul 17, 2007
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    I beg to differ with you on this one point. Volvo started using wideband O2 sensors over a decade ago. Recent models of Chevrolet Corvettes actually use both the wideband and narrowband Lambda sensors in the same system.
     
  5. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Guess I stand corrected however I'm a bit amazed a manufacturer would spring for using them.

    He's still just wanting to make an A/F gauge and on the last "modded" car I built I trusted what I could read using Alex Peper's neat diagnostics circuit: http://www.obd-2.com/

    If nothing else there's a lot of interesting reading on his pages just as there is on http://www.magnecor.com

    I'm too old to be be dealing with this stuff anymore however if my check engine light ever comes on his little device can be a great help in diagnosing the problem. Luckily there are no laws yet that say you can't repair your own vehicles, however during the past 5 or so years they've become almost impossible to mess with at times, and I seriously doubt I'll ever own anything really new again anyway.
     
  6. TheEquineFencer

    Thread Starter Active Member

    Apr 20, 2007
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    I hope this post works, the other two I tried appears not to have posted.
    I had no idea I'd get such a response for asking how to work with a 0-5VDC signal. I'm glad Albert Einstein did have such trouble when he was working on his ideas, who knows where the world would be if he did. I guess it's just a matter of what people do with the available information.
    OK, let's forget the 0-5VDC is driven from an O2 monitor that's a standalone piece of test equipment that does not affect the OEM 1970 Buick Electra 225 Convertible's 455's carbureted engines operation.
    What would be a quick and easy way to take a varying 0-5 VDC signal and compare it to a regulated 5VDC signal, both are powered from the same 12VDC power source, then be able to preset a point when the varying 0-5VDC signal rises above a preset point to trigger an alarm?
    Thanks, marshallf3 for your open mindness. That's why I like the old Dinosauars, use a little high tech on the old stuff to keep it running at peak. I read your profile, you sound a lot like me but better educated. I learn what I need to get the job completed and really could care less if I get the T-shirt to prove it. G/F started throwing the T-shirts out long ago, said my drawer was too full.
     
  7. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Comparator IC and a pot to set the reference (trip point) with. Google should be able to find a ton of these circuits already drawn out, or there will be simple examples in most any comparator's data sheet. LM339 is an easy one to find but as with most common comparators it doesnt sink much output current, easy enough to get around that with about any common transistor.

    PS: I used to have a 1976 Olds 98 2-door something-something Broughm Coupe with the 455. Sadly that was during the time they were building some of the worst engines ever due to early experimentation with pollution control. It was only rated at 170 HP but had enough torque to pull stumps. 21 mpg highway but only 12 in town. The only thing I liked about it was it would sleep 4 comfortably. :)
     
  8. TheEquineFencer

    Thread Starter Active Member

    Apr 20, 2007
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    I'm going to get my dig out a "Heath Kit" this weekend and get started on it. I found one at a State auction and have some "parts' that have been salvaged from some other salvaged equipment. I hate buying new unless I have to. I try to think green when I can. I have a couple of digital displays I want to incorparate into it also that were salvaged.
    My '70 I think is rated 370 HP at 500ft/lbs, really runs decent for a 5500 pound car, the '76 I had was like yours, only 205HP with less torque. Both would sleep 4 comfortably. I like the ride, very smotth, you don't feel the bumps like the newer cars. I went over a set of RR tracks with a buddy in it the other day, he was saying I better slow down, at 55 MPH it was barely noticable. He said if we were in his Crown Vic, we'd been on the roof.
    By the way, a buddy of mine uses his '73 Buick wagon for a pick up truck, did you know a stack of 4x8 plywood will fit inside the "bed' with the seats folded down and you can still shut the tailgate and roll up the back window to keep it dry?
     
  9. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Seems to me I remember that about some station wagons, I think you could do that in our old 1966 Chevy Caprice. It was a "dealer demo" model that came with what they called the trailer towing option. No trailer hitch but it had an SS396 engine in it.

    In my days nothing was ever given to you, you had to save and buy your own car as well as pay the insurance, etc. Even though I come from a "GM Family" (dad worked for GMAC) I ended up with a 1970 VW Bug. The "need for speed" (there were a lot of them at my high school) soon had an Empi header system on it, then a 2-barrel Holley carb and later on I switched to 2,400cc dual-port jugs and twin 2 bbl Weber carbs. It was pretty fast compared to the other "Bugs" - only guy that could beat me had also done cam work and custom built a manifold that took a Holley 4 bbl double pumper. The fastest car at school came about because the guy's dad had been a race team mechanic. 1970 Chevelle SS396, punched out to 427, balanced, blueprinted, 11.5:1 pistons, custom cut roller valve train, 1050 cfm double pumper with velocity stacks etc etc - all the tricks and all done right. Trouble was they couldn't keep the front end on the ground and ended up having to hand manufacture a set of ladder bars that actually extended about 4" from the front of the vehicle. It would still pull a 3' wheelie. Good thing gas was 0.19/gal back then. I don't remember anyone with a hemi but the second fasted car was some sort of Chrysler product with a body style called "Sedan Delivery" - in essence a station wagon without the side windows. 440 six-pack with a ton of parts as well. #3 is the one I'd like to have hidden away somewhere, 1979 AMX Javelin but I can't remember the engine as I don't think it was the regular 390. My list over the years went on and on but nothing was ever anything special.

    At present I have three vehicles on the road as legal drivers. 1978 1 ton Chevy window van, 400 SBC / 350 auto. It only sees a few miles a year if I need to move something. I've got a 1979 Honda CX500 Custom motorcycle, perfectly driveable and almost completely restored. You might remember them as the sport version of the GL500i Silver Wing. 500 cc, 50 HP, 10:1 compresion and a 10K redline. Long story about how and why Mr Honda developed that short-lived line of 500 & 650 bikes that came with many of the firsts in the industry. Extremely easy to work on if you have to, most went well over 200,000 miles with a short and very predictable list of items that would need replacement after a certain amount of time. The "sideways" (from what we normally assume a V-twin to look like) engine certainly draws a lot of attention and very few pictures on the internet do them justice.

    My daily driver is a 1996 Pontiac Grand Prix GTP with the much despised by mechanics 3.4L 4 camshaft engine. Not all that fast but it corners on rails because they "borrowed" a lot of the suspension technology from the Corvettes at the time. Only a few more than 5,400 were built and since engine repairs were so labor intensive there are very few running examples left. I also have two other somewhat unique cars that I hope to restore some day.
     
  10. TheEquineFencer

    Thread Starter Active Member

    Apr 20, 2007
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    Funny you mentioned the Hondas. I just sold a 1989 GB500, single cylinder 'thumper' for the doctor that lives next door. Cute little cafe racer style bike, sounded like a 1 cylinder BBC at idle.
    The VW' are neat, a local "kid' near me used to hold an IHRA world record with a 'Gia at one time. He did have the fastest street car in High School, flat six Porche' engine in a Super Bettle with a turbo. I saw him beat out another kid with a 1970 Boss 302. I think it was the HP to Weight Ratio that was the key.
    The AMC might have been a 401, I have an old freind that was and still is into them. He has a Gremlin he used to autocross with a 401CID in it now. I think he has a set of the "dogleg" NASCAR heads on it, very rare heads.
    Here's a link to a couple of my old cars, http://www.thedinosaurgang.com/default.htm the Vega on the site is the first car I ever "built" the Picture of the green car when it was in primer is how it looked when I sold it to the guy that helped me build it. My lawyer said I had to sell it and give my wife 1/2 the money, I sold the car for $1000 and got out of cars for 20+ years. He still has the car but the engine is in a Station wagon now. Later I'm thinking of asking him if he wants to sell it if it sits a few more years.
     
  11. Jack_K

    Active Member

    May 13, 2009
    115
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    How about an op-amp as a voltage doubler with a 10 volt offset driving a 0-20V meter? That would read 10 to 20 volts and give a true A/F ratio.

    Then, as suggested, use the LM339 or similar comparator to set the trigger point.

    Are you using the Bosch WB O2 sensor? Where did you find the data sheet?

    Jack
     
  12. TheEquineFencer

    Thread Starter Active Member

    Apr 20, 2007
    32
    1
    http://www.innovatemotorsports.com/xcart/product.php?productid=16164&cat=0&page=1 is the link to the one I'm looking to use. It's only $300 plus shipping. The others I've looked at are 2 or 3 times that with a few more bells and whistles. I found a couple of circuits using the lm3914, I did not notice until I read your post about using them like you suggested. If I use a pair of them I'd have a 10-20VDC readout. This has me really thinking now. It looks like I have two differant ideas going now. #1 use the LM3914 and just select the A/F trigger point from the outputs of the LEDs, this looks pretty simple using your idea. #2 The other I think will be a little more complex, figure out how to build a "simple way" to have something like a LM339 and have a +5VDC regulated input for comparison to the +0-5VDC coming from the Monitor and be able to select a trigger point. I've built a couple of Narrow band Monitors with LM3914, but with the Narrow band sensor, the 0-1VDC signal is not linear and is only accurate at 14.7 AFR.
    I'm going to do some more reasearch into using your idea. I think I have link to a print for a 5VDC input with a 12VDC supply with 10 LED outputs. and also one with two working together. I guess I'll have to just post the link unless I draw it out myself right? Do they allow copy and pasting of prints from the 'Net on here?
    I'm a little slow learning, but once I get my mind wrapped around how things work, I can run with it then.

    Thanks, Floyd.
     
  13. TheEquineFencer

    Thread Starter Active Member

    Apr 20, 2007
    32
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    see what you think about this and how it will work.
     
  14. SgtWookie

    Expert

    Jul 17, 2007
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    Gee, the '76 Olds engines weren't as bad on gas as the '74-'75 models.

    I had a '66 Dynamic 88 convertible that was fire engine red with a white top, interior, and a 425 ultra high compression engine under the hood, with Cherry Bomb mufflers. It was a big and heavy car, but had oodles of torque. A real lead sled.

    Went through a series of Cutlasses, '70, almost bought a '72 442, '73, '74, and a '76 - all had 350 4-bbl's, the '70 had a high-compression engine.

    The '73's were still pretty good. The '74 and '75 were pretty loaded down with smog stuff, and the 74 had lousy mileage. In '76 they made some improvements. One of the things they did for emissions was retard the camshaft timing by 4°; gearheads would buy custom timing sprockets to get them back on time.

    Anyway, I really have to run - going to be late for a class.
     
  15. marshallf3

    Well-Known Member

    Jul 26, 2010
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    True, we not only got hit by insurance companies about horsepower but also from California because of their smog.
    Used to be even the presence of FAKE hood scoops made your insurance higher.

    The entiire public had to suffer.
     
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