Narrow band O2 LED meter

[sypher]

Ok for anyone who’d rather make than buy a narrow band LED mixture display.

List of parts

(1x) LM3914N and I C socket 18 DIP
(2 x my choice) 4K7 cerment pot’
(1x) 16v 10uF electrolytic cap’
(10x) LEDs standard 5mm 5v
PCB, whether it’s fabricated from a copper coated board or wired on perf’ board.
and finally a project box.

Now that you’ve got the parts required you need to put it all together, the layout for this device can be found at http://www.national.com/pf/LM/LM3914.html National Semiconductor page.

NOTE; I have used two 4k7 pot’ instead of that stated on the tech’ sheet so I can adjust the brightness of the LEDs and the illumination of a certain LED at a specified signal input voltage,, eg; 1st LED on @ 100mV, 2nd LED on @ 200mV etc etc, but obviously this is your choice.

Now for the cheap way to adjust you meter before installing it into the car, rather than buying a desktop adjustable voltage source, you buy a 1.5V battery eg; AA, and two pot’s, quite large as you are going to be soldering wires to them and need to be adjusted easily.


The signal / adjustment voltage is on the line between the two pot(s), adjust as required to give your desired voltage. .please remember you will need to have your PCB powered at this point and a digital volt meter DMM. I used two AA battery cells to give me 3V and I connected the NEGATIVES of the two separate voltage sources together.

I also prefer to have wired in bar mode not dot mode as I like this display better, you get the LED which is corresponds to the current signal voltage and all previous where as on dot mode you only get one LED at a time...To achieve bar mode connect pin 9 to +V supply, to achieve dot mode leave O/C.. Once you have built and set up your device you now have three wires to install, 12v, 0v (gnd) and O2 signal which I believe is pin 19 of the ecu multi plug.

All parts can be cheaply bought from Maplin Electronics, although I haven’t got one fitted to my car as it has no engine. I can assure you that this works as I have used it for diagnosis of O2 probes (as it’s WAY quicker than a DMM display) and WOT lean condition that ended up being fuel starvation.

DISCLAIMER; I have given this information in good faith and tried to be as accurate as possible, any modifications to your cars electrical system is at your own risk that includes personal injury and property damage. It is your responsibility to check ALL aspects of project before attempting this. Feel free to post mod’s / revisions as needed.

Stu.

 

[AJ4]

How did you wire it up for FSD, + volts or 0 volts ?

Reason I'm asking, I fixed an autometer one a while back that uses the LM3914, but it seemed to work in reverse, ie, 0volts was FSD ( rich ) and 1V was nothing ( lean ).

Must be the way they had the input setup, using the lambda sensor as a current source instead of a voltage source... Not sure which way is better or what difference it makes though.

On another note, there are a couple of simple mods you can do to improve the display, like wiring it into your dashlights so the LED's go to half brightness when you turn your lights on ( stops getting blinded by the feckin thing at night ) and setting 'alarm' mode that triggers on a particular LED to either flash the whole display or flash another big red light somewhere

Also worth checking out exactly what Lambda sensor you have if you want the thing to even be remotely accurate - I have a 1V max sensor, some people have 1.2V, I 've even heard of 1.5V.... :shock: Obviously which sensor you have makes a big difference to what you read.

 

[sypher]

yeah, i read somewhere that people have different O2 signal voltages so i guess it'll have to be upto them to measure the signal themself as i can't find any data as to what the "odd" nissan O2 signal is at stoichiometric!! on the 0.9v rich probe the signal is 450mV. and to the best of my knoledge all narrow band uses voltage signal, wideband is current sensing, and any ecu parramaters i've seen for O2 is V.

setting 'alarm' mode that triggers on a particular LED to either flash the whole display or flash another big red light somewhere

please understand the following is just my opinion, "I" wouldn't want the display flashing or illuminating a seperate light source as when you take into consideration the way the engine is run ( 0.9V for eg; ) car idling or mot spec' RPM with no load gives fluctuation of above=450mV=below=450mV=above etc etc when engine in medium to high load 900mV and when you lift off the throttle and engine is in over run, the injectors aren't working so you get 0mV so as you can appreceate thes condition O2 signals happen in every driving cycle providing engine warm.

I have thought about using an 87a style relay to switch the supply to the LEDs to reduce current to them initially before IC control using the side light illumination to control coil, also i am next going to be using clear look LEDs as i think they look alot better than the coloured ones.

Stu.