DIY digital A/F ratio gauge **PICS ADDED**

[gobtool]

There's a lot of people on here running a LC-1 wideband, mainly because they're cheap.  They're very useful for input into other systems, but to actually monitor the AFR you need a laptop.  For me it was kinda a lot of trouble having to hook up my laptop every time I wanted to do some tuning.  The Innovate XD-1 gauge is available, but it's about 180 dollars.  Then I came across this.

http://www.2gnt.com/www/corbin/dvm2.html

It's a write-up somebody did on how to make your own A/F display using a LCD display to show voltage.  I did a search on here but I don't think this has ever been talked about.  Anyway, it's a really great way to get a display for A/F really cheap.  I had an extra display around so I wired it up and got it working.  I did mine a little different than the instructions though.

Most of the displays run on 5V DC.  If you could find one that ran on 12 V it would be nice, but other wise you'll have to find a way to get 5V.  The best way to do this is to use a littel 5 volt regulator.  It has three pins.  The first one is the input (up to 35v), the second is ground, and the third is 5V output.  The general part number on these is 7805.

That website has you build a little voltage divider circuit to calibrate the meter.  Since I could actually monitor the A/F ratio with my laptop, I just used that to calibrate with.  Also, the display they used had a potentiometer on the back to calibrate it.  Mine didn't, so I just tried different output values on the LC-1 until I got the correct reading on my display.

I did my voltage divider circuit for the input in the car different as well.  I couldn't find any instructions for my display, but it did have a 100K resistor tied to the input and a 1 K resistor going over over to ground.  This was giving me a voltage readout 10 times what the actual voltage was.  I thought this would be good.  I would just program the LC-1 to output like .8V for an AFR of 8, and 1.6V for an AFR of 16.  It worked, but my display wasn't putting in the decimal place.  Instead of showing 12.4, it just showed 12.  I changed the 1K resistor that was going to ground up to a 10K resistor.  This let less current go to ground, and gave me a multiplier of 100.  Then the display showed 124 for a 12.4, which is fine by me.

I probably just did a really good job of confusing everyone.  I'll try to take some pictures today.  I'll try to make up a little schematic as well.

[mystang]

ha ha its like my greedy profec b when its 10 lbs of boost it reads 100 and when it is 5 ponds it reads 50


Yes this would be great if you could get a write up on this, because i also run a lc-1 andhave been wanting something like this for a while. Also with the schematics(sp?)  could you also take a picture and maybe make some labes it might be me but i get confused all the time with shchematics.


If this works i would also make this a sticky.

[gobtool]

Yeah I'll go take some pictures and try to work on a schematic.  I'll try to find a link to a display that would be appropriate as well.

[mystang]

Thanks how is the "refresh" rate on the read out is it instant, or does it jump around?  Also what display did you use if you know

[mystang]

when you say you had a 100k resistor o he input i presume you are refering to the 02 signal, so what you did compared to the electronics is just use a diff display and use a few different resistors, but that is it hardware wise?

[Allen Vos]

That sounds awesome , I would like to try and build that as well.

Let me get this correct.  Your were showing an acutual AFR not just voltage????

Keep us posted.  Sounds like your on the right track.

Good Stuff

[gobtool]

Yeah, it shows the actual air/fuel ratio.  The display refreshes probably 2 or 3 times a second.  The display I used was made by Analogic.  The part number was AN2575.  It was in a piece of test equipment that we had around.  It's got 30 pins on the back, and I didn't have an instruction book, so I had to go by how it was hooked up before.  Basically there was just a power wire (red), a ground wire (black), and an input wire.  The input wire had a 100K resistor inline with it, and then it went onto the top left pin on the back of the display.  Then there was a 1K resistor going from the top left pin over to the pin directly to the left of it.  Hooked up like this, the display read 10 times what the actual voltage was.  I thought that this 10K resistor was tied to ground, but it wasn't.  Apparently it goes to some kind of setting on the display to change the output.  I wish I had an instruction book for it but I haven't been able to find one online.

The pictures below should explain everything better.  Can anybody guess what the red thing is that I used as an enclosure?  Most of you probably have one lying around somewhere.

By the way, I looked back over the instructions on the link I posted, and I'm pretty sure that that display only shows you the voltage from the O2 sensor.  While that would be helpful, it's not nearly as helpful as the actual A/F ratio, which is what mine shows.  I'll try to get a schematic made up as well.

[Allen Vos]

Does it have to be a specific display, or would any old digital display work??

[gobtool]

I'm pretty sure any display would work, but it might be hard to figure out how to wire it if you don't have the instructions.  It might be better to buy a new one that comes with instructions, but if you had an old one laying around it sure wouldn't hurt to try it.

[gobtool]

Alright, I've been thinking about it and I believe that you would be able to use about any display and just hook it straight up to the output wire of the LC-1, or any device you can set the outputs on.  Just start out with the LC-1 to put out like .8 V for an 8 AFR and 1.8 V for an 18 AFR, and everything in between should come up right.  It will just show like .147 for an AFR of 14.7, like mine shows 147.  I had to change mine because I couldn't figure out how to get it to show decimals.

So has anybody got a guess about what I used as a enclosure?

[Andy Dorsett]

What is wrong with this?

http://www.diyautotune.com/catalog/analog-wideband-gauge-display-p-57.html?osCsid=0ef85b869ff2d9503f2d05a5db2780b6

[gobtool]

I didn't know that product was available.  It should work fine give a real good idea of what the air/fuel ratio is.  I would still prefer to have an actual readout of the number, but that gauge is about 1/3 the price of the XD-1 made by Innovate.

[mystang]

yeah gbtool i was looking at the lc-1 and you can just turn the other output to read the wideband (7.35-22.39)  which gives a range of 15.04 now if you set the voltage to .735 for 7.35 and 2.239 for 22.39 then it gives you a range of 1.504 so it will read the same just the decimal point will be off.  Now here is the question do resistor drop voltage or current, because pretty much the only thing that you would be doing is making a volt meter, so would i just need to have the voltage regulator for the back light and a power ground and signal straight from the lc-1 without all of the resistors?

[gobtool]

Resistors limit current, but there should be a voltage drop across the resistor.  My meter doesn't have a back light, so the 5V was to light up the actual numbers.  The one on the link I posted had seperate inputs for the display itself and the backlight, I guesss so if you didn't want to use the backlight.  You should be able to just hook the LC-1 straight up to the display.  The display I used only needed one ground.  I'm sure it would be best to ground the display at the same point you grounded the LC-1.

[Turbo383TA]

Hey Gobtool check out www.allelectronics.com they have some killer deals. I dable in electronics, and get most of my stuff through them.

[Daddy]

Cool thanks for finding this.  I've been looking for a DIY digital A/F guage for a long time cause it really is just a voltage meter.  The one hurdle that I couldn't figure out was how to multiply the output voltage from the wideband by 10 so it could easily be read into a standard 2 1/16 voltage display for a car.  I know a transformer would do it, but I haven't looked into too many and I don't know if I could get one that's small enough for cheap enough.

I'll have to read that page some more later, I gotta get back to work now.

[Andy Dorsett]

Cool thanks for finding this.  I've been looking for a DIY digital A/F guage for a long time cause it really is just a voltage meter.  The one hurdle that I couldn't figure out was how to multiply the output voltage from the wideband by 10 so it could easily be read into a standard 2 1/16 voltage display for a car.  I know a transformer would do it, but I haven't looked into too many and I don't know if I could get one that's small enough for cheap enough.

I'll have to read that page some more later, I gotta get back to work now.

A transformer will only step up or down an ac voltage.  Stepping up a dc voltage takes an active electronic device like an op amp.  Also a cheap gauge will simply have a movement in it that requires a good bit of current.

[gobtool]

Thanks for the link Turbo383TA.  They've got a lot of stuff on there.  Too bad all the displays that I saw were like for 16 characters or 2x20 or something, and not any with like just 3 big numbers.

+1 on the having to have AC for a transformer.  I wish I knew what made my gauge multiply the voltage like it does.  But I would be just as happy with it showing .147 instead of 147. 

I really think that Mystang has the right idea in thinking that we can just hook the output straight up to the display.  Then all you really need is the display and a little voltage regulator.

[gobtool]

I bid on a lot of 2 displays on Ebay that are real similar to the one I'm using.  There made by the same company, Analogic.  The main reason I bid on them was to get an owners manual.  The thing looks like it's about 3/4 of an inch thick.  The displays are designed for a 0-10V input, with an output (on the display) of 0-1000.  I shrunk down the link so it would fit better.

http://cgi.ebay.com/ANALOGIC-MEASUROMETER-II-DIGITAL-MONITORS_W0QQitemZ120080769682QQihZ002QQcategoryZ58278QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

[Daddy]

A transformer will only step up or down an ac voltage.  Stepping up a dc voltage takes an active electronic device like an op amp.  Also a cheap gauge will simply have a movement in it that requires a good bit of current.

Aaaaaaahh, thanks for clarifying that.

<------------mechanical guy that now feels like an idiot

[mystang]

yeah i will have to do a little research to see what all of the connections on the back of the display do  hey gobtool or someone could you tell me what you think by looking on that link that you originally found do all of the connections that go to the bottom of the "divider circuit" do all of those go to ground?  but run through a 100k resistor?

[mystang]

update on a/f meter me and gbtool put our heads together well i asked the question he did the calculations, and we think we have found out a way to setup the display and "manipulate" the 02 input signal so that it will read 14.6 instead of .146 or 1.46 etc.  and it will read correctly for the rest of the range.  so i am going to order the same display in the original link and enclosure, but i am going to use a little different resistor setup and wiring on the back of the display.  Gbtool found the manual for the display and after looking at it we found out how to change the "scale" so that the decimal place is in the correct position.  so hopefully next week i will have a working prototype that all of us turbomustangers can make a digital a/f display that will work with our lc-1(well atleast the ones that are not permanetly attached to the jackstands) 

[Turbo383TA]

I used to use one of these on my buick. Very cool. Maybee you could incorporate some of the functions in your design.
http://www.fullthrottlespeed.com/items~CartId~%7BE48FD47A-2B02-4D77-B2B7-CD5711AC32DFEVEREST%7D~Cc~SCAN~iTpStatus~0~Tp~~Bc~.htm

[mystang]

I used to use one of these on my buick. Very cool. Maybee you could incorporate some of the functions in your design.
http://www.fullthrottlespeed.com/items~CartId~%7BE48FD47A-2B02-4D77-B2B7-CD5711AC32DFEVEREST%7D~Cc~SCAN~iTpStatus~0~Tp~~Bc~.htm

Well incorporating a scan tool may be a little/a shit load above my level considering i was having trouble figuring out resistors to use(ha ha)  I am just trying to make a cheap reliable and accurate readout for my lc-1 so that i can see what is going on without having to have my laptop in my passenger side seat all the time.  For me this is more of a idea so i can see what is going on even though i tune with my laptop this will just give me that warm fuzzy fealing inside.  Kind of like after you set your boost you shouldnt have to woy about is so why do you have a boost gauge?  Same idea here i just want to make sure everything is going right cause as we know it only takes one of the many sensors going bad to mess everything up and when we are running turbos on computers that were not  ment for it or engines i would like to know as much info as i can.  I am also thinkiing of incorporating a seperate voltage regulato so the led wont light up unless i have my drving lights on so i will have to have two voltage regulators, and hook it up to my driving lights via relay or something so the back light dosent come on unless the headlights are on, but will have to see.

[gobtool]

I used to use one of these on my buick. Very cool. Maybee you could incorporate some of the functions in your design.
http://www.fullthrottlespeed.com/items~CartId~%7BE48FD47A-2B02-4D77-B2B7-CD5711AC32DFEVEREST%7D~Cc~SCAN~iTpStatus~0~Tp~~Bc~.htm

Well the link isn't working for me, but I can probably tell enought by the picture.  I'm with Mystang in thinking that a scan tool is a little over my head as well.

As for the idea of running two regulators, that's about the easiest way I can think of doing it.  I assume the display has an LED backlight, so it will use basically no electricity and pretty much never wear out.  I would probably try it first with the backlight on all the time and see how it does.  You could always put a switch on it, but then you would have to flip it when you turned your lights on.