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calibration of a lm3914

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woogoo

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hi guys,

I just made a variable Air/fuel ratio gauge from a lm3914 (0.58v to 0.94v)
and i want to do a calibration

I want to know how you can built a variable 0 to 1 volts power supply I search over internet and I saw people using the lm317 but all power supply shematic I saw are 1.5v and up... if its posible to draw me a shematic in discrete, i dont want to buy a ic if its posible.

Thanks
 
Use a regulated supply and put together a voltage divider to get the lower voltage. Keep in mind that the circuit you power might draw suffiicient current to introduce some error so best to actually measure the voltage once the circuit is connected. Bear in mind that this will work for low current application only.
 
thank I feel a bit stupid ! i did some search for voltage divider and I buit a circuit from a regulator and and a potentiometer 10k and i get into the range

but while i was testing my Air/fuel ratio display I saw a little trouble when im in the bar mode the light is clear to red they light and close , but when i go to DOT Mode , if the dot is at half display bar the led in middle are bright but the half part of the bottom still glowing a little, that make the reading hard.

And when i am in bar mode at .50v then i switch to dot mode the voltage go up to .54v ... the range is not the same from dot to bar mode is that normal???

here a shema of what i did for the lm3914 display:
**broken link removed**

I made a power supply from a 7806 with a potentiometer with some capacitor too.
Both are connected to a transfo 9v 210mA and I connect my lm3914 pin 5 to the center pot leg

any idea for my little trouble there
Thanks
 
Your circuit lights too many LEDs because it is too simple and doesn't filter the normal voltage fluctuations of the O2 sensor.
Here is a project that has a filter plus lots of other improvements. You don't need the quad opamp and quad comparator if you don't want the other improvements, a filter can be made with a 100k resistor in series from the O2 sensor to pin 5 of the LM3914, then a 1uF capacitor to ground at pin 5.
**broken link removed**
 

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thank for the hint about o2 fluctuation but the circuit is not on the car right now. I use a variable supply with not much fluctuation , Im trying to do the calibration for 1 led a .58 v and last at .94 but i dont know why the closer i get is .54 to .68 you guys see any bad value in variable resistor? or maybe they not at the right place?..

My trouble is not the sensitive the led in BAR mode go up each 40 or 50mv
the light just keep lite glowing pass that voltage in dot mode and the volts reading on my multimeter change and get .05v up when i switch...

and I have like 14" of wire between the led and the lmcircuit is that maybe too much ? a 10 uf capacator at the V+ of the led maybe do nothing in my case?

Im testing the circuit and maybe will add 2 more 3814 later for a 30 led display of .5 to 1 v later
I cant buy a wide band o2 for now and I need something to see with the best precision where is the reading.. we have a racing car running with stand alone ecu and we require a good reading for tune the ecu corectly.


Thank for your input!
 
You can't tune using a standard 4 wire sensor. Don't even try. It's not meant for anything but stoich switching and you'll likely just damage the car if you use it as any sort of reference.

Most dyno facilities have wideband rentals. UEGO sensors/controller are so cheap now. (well, relatively)
 
I agree with you, I will have to push my pilot to buy a wideband I saw some KIT with the controller and thing like that but can i get only the sensor Bosch LSU 4.2 sensor at 75$ and do a circuit for read it like on the 1volt one?? wide band its 5volts so lm3914 can work there too nah? if you really need a controller anyone have an idea how to DIY one?

I can go for a wide band at 75$ but not a full kit at 399$ US! I know some shop with a Wideband but they tune on the Public road ... we have a heavy modified cars we cant take the risk and dyno time can be costly .
 
You can get the sensor, and I have seen some LSU4 schematics, but it's not simple or easy. UEGO sensors require quite a bit of active control to work properly. They are not plug and play like a narrowband sensor. For a race car that your tuning on the edge I would never make my own. Buy a properly calibrated LSU4 controller and sensor. Some people I talk to won't even trust regular branded UEGO controllers, but I think that's going a little overboard.

If you want a DIY kit, you can go here:
https://wbo2.com/

Still, with an expensive racecar I would try to get something with a little more backing. My cars are all pretty darn cheap, and I have an older L1H1 UEGO.
 
s*** I cannot built this kind of system to control the wide band , I guess i will have to buy a complete system .. Do you know any good for price system avaible in canada.. (damm custom taxe when you order from the us)
 
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