Well, not entirely. Bill and I wanted to put out a little "freeware" type DIY meter that we came up with. Yes, it's based on the LM391x series, BUT it's not the LM3914 - it's the LM3915 - the logarithmic version of the LM3914. The trick to it is however, is to have TWO of them and "reverse" one of the chips so the logarithmic values are aligned properly with the output of the stock sensor. The other trick is to NOT measure the stoichemetric area with a bunch of LED's, since it obviously represents such a narrow range - other than watching a bunch of LED's flash around when the ECM is in closed loop, it's pretty useless. Instead, we have a single LED as a reference point, that indicates when the O2 sensor is in the stoich range. This makes the meter a 21-LED meter. Since it's DIY, you can choose the color scheme that suits you best, too.

So we've put a "gap" resistor between the two LM3915's, and we have one center LED that's always on - to indicate the voltage is in the "stoich" range (.25v-.75v) - this gap CAN be tailored to your liking - in fact, Bill whipped up a really nifty Excel spreadsheet where you can change the gap resistor values and final comparator values to tailor the curve to your liking. We finalized on 25k for the gap resistor, and 50k for the final resistor. I asked Bill about using a potentiometer but he said they tend to "bounce around" with values, and didn't reccomend it.

The other feature we integrated into the meter is that it's bargraph style - but before you go groaning and rolling your eyes, it's CENTER WEIGHTED. In otherwords, the center LED is your reference point - and a lean condition would cause the bargraph to move outwards from the center. A rich condition would cause the bargraph to move the opposite direction - from the center. This way you have a reference point. No more silly bouncing around LED's and not knowing where you are in relation to lambda.

We've also incorporated a high-impedance op-amp as a buffer so that there's hardly any current draw on the O2 sensor, a problem with some of the other methods since it interferes with the ECM's operation. We put a voltage regulator on as a precaution, too.

I will however say, that this is for a NARROW BAND O2 SENSOR. It's not meant for Wide Band, nor is it nearly as accurate. This setup is merely for folks who would like to be better informed of what their stock sensor is saying. For this same reason, we can't assign A/F ratios to the LED's, but it'll certainly give you a much better (and certainly quicker) representation of what's going on than any DMM, ECM, or 10-LED-LM3914-based-cheezy-AF-meter can.

So the neat part is, not only do we have the schematic that Bill whipped up, but it's tested, and Bill managed to route it on a *single sided* board. We will gladly have boards made if there's enough interest in it, and the parts are readily available from Digi-Key. Bill's board is routed to fit inside a standardized enclosure also, so it can be mounted cleanly somewhere.

Niether Bill nor I have time to assemble these units, so please don't ask. If you want to help someone by building them one and charge them a small fee for assembly, we're fine with that. Just don't try to manufacture them and call them your own! Otherwise, enjoy!!

7/4/2005 - updated links!!!!

 

If/when you do some boards, I'll take a couple.

 

We'll probably bring you a couple when we come up there in June..

 

Huh... interesting... do you care to share the PCB layout (I'm actually pretty good at building this kind of stuff, but terrible at laying out a PCB)? Any timeline on boards being available?

 

Do you have a parts list for those of us that are too lazy to break down the schematic?

 

Working on a parts list right now.

Boards probably available next week.

 

What format would you like the board layout in? It's pretty small, so I don't think it's something a DIY'er can replicate easily. (If you can I want to know how you did it!)

Here's the BOM (bill of materials.)

7/4/2005 - updated links!!!!

 

I donno, I've got a few bits of PCB software somewhere…, or anything that I could see it at the correct scale (PDF or something?). Not sure how I'm planning on transferring it, I'm wondering if there's something that can be done with a laser or inkjet printer… By hand?

I did get my mitts on a few LM3915N-1's
and I probably have everything else sitting around besides the LM358N (actually kinda funny since I'm not at all an electronics guy...). What is a LM358N anyway, is there anything that can be used in it's place?

 

For correct scaling/resolution you would need to have either DXF or Gerber-X formats.

LM358 is just a generic dual op-amp chip. We use one op-amp strictly for high-impedance buffering so as not to excessively load the O2 sensor and the other to implement a 2nd order active low-pass filter. Any generic op-amp that's unity gain stable and can run from a single 5V supply will work, but it should have a gain-bandwidth product of less than 1MHz...and of course it has to be pinout compatible.

 

Dumb question.... What O2 sensor do use with this?

 

This is for the stock NARROW band sensor. It does NOT work with a wideband!

 

Okay, that's what I thought. Where does J1 plug into? I was thinking that went to the O2 sensor but it is 3 pin and the O2 is 1 pin.

 

You need 12V and ground.

 

Heh, nice answer to give right after I said something along the lines of "I'm in no way an electronics guy"


Heh, slower and in English? I'm not sure that even that would help…


heh, I think I can get that (at least I understood most of what you said that time), and the other one is just a 5V voltage regulator (funny, I tried looking it up in a few places and found that it's discontinued from most sources)… Now just working out the board. Did you use one of the online PCB sites or something?

 

DXF is an AutoCAD file, I can export to a DXF file.

Gerber is the standard format that most PCB fab shops use. Most "modern" PCB layout software packages will export to Gerber files.

I will probably have some boards available here in a matter of days, all you'd need to worry about really is parts...unless you just like to try making PC boards.

 

Anyone plan on making couple pcb? I might need couple.

MAth

 

I WILL buy one of the boards do you accept paypal? just let me know how much and where to send payment.

blue_IROC_Z28*hotmail.com (replace asterisk with @ to email me)

 

Nice work. I'm in for a couple of boards.

 

Grr, yea, not sure what I was thinking… Yea, I can do DXF, might be able to do gerber. If you want to get scaling right and make it accessable to more people it's easiest to just put it in a PDF.

huh, that would work also.

 

I was looking at this circuit and was wondering what VCC meant. Is this 12v (Ign) in from the car?

 

I hope to have some boards ready in a week or so. If you'd like to order one, send me an e-mail to ken7382@hotmail.com with "AF meter PCB" in the subject.

We're asking $8 for each PCB.

 

PDF scaling isn't as accurate as you might think, besides the resolution with a PDF file is nowhere near good enough, at least not with the tools I have.

We bring in 12VDC, then regulate that down to a constant 5V that powers the board...that's VCC.

As for what the letters mean...it comes from the voltage applied to a basic emitter-follower transistor circuit, where you would apply voltage to the collector of the transistor. So "V-C-C" actually stands for "Voltage-Collector-Collector". You might also see the term "VEE" to represent ground or a negative supply...VEE would be "Voltage-Emmiter-Emmiter". The FET equivalents are VDD for Drain voltage and VSS for Source voltage.

Just a cute little tidbit of tradition for anyone that cares.

 

I've seen, and subsequently done drilling/gasket/spacer templates in PDF and never seen a measurable error from them. You just need to set the margins to something that any printer could print and then size it to be full pages and it comes out fine.

Thanks for the Vcc… history… lately I've been looking at chip pinouts and was wondering exactly that.

 

OK, I'm going to send out the first orders today; I have plenty of boards right now if anyone is still interested.

I've also bought enough parts to make a couple of complete parts kits including a black enclosure. E-mail me if you're interested.

The parts placement guide is up, too.

7/4/2005 - updated links!!!!

 

do you have a picture of the pcb or of what would it look after assembly.

 

Not yet.. Bill probably has a pic of an assembled unit. I'll have one or two assembled here soon myself.

 

Ken,
I'll take a board. Can you put me on the list please?
I'll send you an email when i get home about postage etc..
Ben.

 

I think I would be interested in a board too If anyone gets a chance of posting a picture of what one looks like that would be great. Then I can make up my mind if and where to mout it. Looks pretty neat to me, great work!

 

Hey Ken have you mailed my boards yet?

 

Whenever someone gets theirs working I would like to see the results compared to dyno AFR readings to compare how accurate this is.

 

That might be tough to do. This won't give you an actual number, just a bar-graph representation. I don't think its really a matter of accuracy so much as a matter of resolution. What we're doing is trying to improve on the off-the-shelf meters that are available out there now for stock NB sensors. What they do is take the entire range of the sensor and divide it up linearly across 10 LEDs. With the whacky response of a NB sensor that results in about 6-8 center LEDs to cover the stoich region and only a couple on either end to show rich or lean, not a lot of resolution there. So what you see on the meter when either idling or cruising is a bar-graph that's bouncing back-and-forth almost from end-to-end. What we've done instead is basically ignore the stoich region and split up the rich and lean regions over 10 LEDs each, and done it logarithmically (this is the important feature!) to match the sensor response VERY closely.

I do have one in my car. What I did is set it up so that at either end of the stoich range should light one LED on either side of center depending on whether its on the rich or lean side. So instead of the meter bouncing back-and-forth from end-to-end I see it going back-and-forth only between one LED on either side of center (sometimes 2). That way I can see the ECM working. Now, with my engine set up the way it is I was fully expecting things to be a little on the lean side, and that's exactly what the meter shows. I have a "lean stumble" on takeoff or sharp acceleration, and that's exactly what the meter shows. When I step on the gas the meter will dip all the way to the lean end very briefly, then go to the rich side as long as I'm accelerating.

I also learned something else interesting that I didn't know. When going down a steep hill and I let off the gas, I can feel something "kick in" and help slow the car down. It almost feels like a very mild engine brake. I've also noticed this in my astro van. After installing the A/F meter I watched it when this happens and it is showing a full lean condition at the exact same time that this "engine brake" kicks in. I've been wondering for a long time what exactly was causing this effect...now I know!

End babbling.

 

I sent out a batch Tuesday; when did you pay for yours? What is your name?

 

I was under the impression that that was a fairly common thing, especially with TBI stuff. I know that the crossfire documentation actually specifies that the injectors close under decal in the FSM

BTW, Ken, haven’t seen mine yet…

 

Okay, I finally sat down and built my own this weekend. It works exactly as I imagined it, however it's shown me that the O2 sensor in my truck is pretty much shot; it just oscillates between totally lean and stoich. I'm lucky if I get 1 rich LED to come on when I stomp on it, so I'll be replacing my O2 sensor soon.

Here's a few pics of my assembled unit.









Once you've assembled it and powered it up, the last pic is what you should see; the first 10 LED's and the center STOICH LED should be lit.

I will tell you that you HAVE to be careful soldering this board; the traces are very small and while they won't lift off the board (at least they didn't for me) you can easily bridge traces. I had about 5 or 6 traces that were bridged that I couldn't see with my naked eyes; I had to use an Optivisor to see where I had messed up. Solder wick was handy in removing excess solder, too. Cutting the enclosure was pretty simple; you can do it with a Dremel or an X-acto knife just as easily.

NOTE: You may want to take a black Sharpie pen and color the SIDES of each individual LED to prevent light-bleedover between the LED's. Bill said he has a lot of trouble with bleedover, so I tried this per his reccomendation and it works great.

7/4/2005 - updated links!!!!

 

Yeah I get a lot of light bleedover between LEDs, especially the red.

You should have a small-tipped iron for these, a large tip will make things tough. Also, some water-soluble flux will make soldering a lot easier. Plumber's paste flux works very well, just brush a little on the pads after the component is in place. It'll bubble and smoke alot when you put the iron to it, but its supposed to do that so don't worry. When the board is assembled use an old toothbrush, some dish-soap and warm water to clean all of the flux off. Don't worry about getting the board wet, it won't hurt anything...just make sure its dry before powering up.

 

Nice… looking at it I’d probably consider building a little jig to hold the LED’s perfectly straight and putting a dab of glue on them before soldering them to the board so they stay aligned or put a piece of smoked Plexiglas in front of them (yea, I’m that **** retentive)

 

Could you post the source info for the enclosures?

TIA,

 

The Digikey part number for the enclosure is included in the Bill of Materials. Ken posted a link to it in an earlier post.

 

1 question from me. Can tjis be used effictivley at WOT to see if you are runing LEAN?

 

That's precisely the idea behind this. It tells you exactly what the O2 sensor is seeing, real time. If you're running lean, it'll see it.

Just as a comparison, I bought a Jaycar kit which has a digital display as well as a bar or dot graph. It only updates about 2 times a second. The other AF meters out on the market only measure a few LED's worth (extremely low resolution) of the actual spectrum. One of the available AF meters (Edelbrock I think?) only has a few LED's! There's another one that has 30 LED's, but it still doesn't measure logarithmically like ours does to closely follow the stock sensor's output.

Another note: I'm shipping the kits with 10 red LED's, 1 yellow LED (for stoich) and 10 green LED's. I've been assembling mine as red = lean, yellow = stoich, and green = rich. Of course, you're welcome to do it any way you want.

 

How does this compare to the LM-1?

http://www.innovatemotorsports.com/lm1.php

 

That LM-1 is for use with a wide-band sensor, the DIY meter is for use with the stock narrow-band sensor. Aside from that, the LM-1 is digital at a rate of 12 samples per second, better than the ALDL stream yes, but horribly slow for a $350 device in my opinion. Although the DIY meter's display "seems" digital, it is an analog meter. This means it is continuously sampling in "real time". Also, there is no on-board memory storage on the DIY meter, what you see on the display is it.

The LM-1 would be good for doing lots of datalogging, but at 12 samples per second I wouldn't pay $350 for it.

 

Fantastic. I just keep wondeing how the hell you guys come up with stuff like this?

How you put things together and make sure they interact as supposed to.

GOOD STUFF!

 

Helluva concept ain't it.

 

Double post

 

I wish to buy two boards/ can you also give me a price for the kit w parts.
Thanks
Ed

 

How 'bout a part number for the equivelant LED in blue? I'd like my stoich light to be blue. =)

Also, is there any chance of modifying the design to have a single LED lit at a time, rather than a "bar graph"?

The parts for mine should be here later this week. Should prove interesting!

Thanks guys.

 

Geez some people....just never happy. heheheh (Just givin' ya crap man)

I don't think you can get that size LED in blue Mark, not from Digikey anyway.

I was going to try to lay it out to select either "dot" or "bar-graph" mode with a jumper, but doing it on a single layer proved to be next to impossible. I don't remember exactly what it would take for dot mode, but I'll have a look when I get a chance.

 

When the center LED is lit, is that "approximitely" the same as a 14.1 AFR? If that is the case, when you are at WOT the AFR should be around 12.7. How do you know that is the case? It seems like it will just show a Rich at WOT which wouldn't be the case. Maybe I am all wrong with this. I'm not sure.

 

Boards are $8 and kits are $40. Prices include shipping to lower 48 United States.

Kit includes ALL parts necessary except wire to hook it up, INCLUDING the enclosure (black.)