Simple O2 meter with LM3915

[wuemura]

Hello, i really dont know what type of O2 sensor my car uses, i know that is 4 wire type, looks like a cigar and has a hole in the middle.
About printing, here is the tip, load the PDF in to Photoshop.

In resolution set to 600 pixel/inch, grayscale mode, 16bit and remove (uncheck) anti-aliased option.

Duplicate the layer, so it will became more dark, press CTRL+E to join this parts, press CTRL+A and CTRL+C, create a new layer for printing, press CTRL+N to create a new layer, select A4 paper type, resolution set to 600 pixel/inch, 16bit and transparent background and paste the design (CTRL+V).

Duplicate the layer if you want one or more bord designs in on sheet, print the design, Photoshop will complain about the size, just ignore.

You are done, the design will be printed at the correct size.

 

[audioguru2]

A 4-wire O2 sensor has 2 wires for its electric heater, so it warms up fast. If the heater burns out or becomes disconnected (by tinkering?) then the car's computer flags an error.

 

[wuemura]

A 4-wire O2 sensor has 2 wires for its electric heater, so it warms up fast. If the heater burns out or becomes disconnected (by tinkering?) then the car's computer flags an error.

Yes, and the engine will not start.

 

[audioguru2]

But the car's computer doesn't know the difference between a real heater in an O2 sensor or a resistor, does it?

 

[wuemura]

But the car's computer doesn't know the difference between a real heater in an O2 sensor or a resistor, does it?

Don't know, in my car (Fiat Siena) it doesn't start the engine if i disconnect the O2 connector.

 

[gearhead98]

if you are using the sensor that is already on the car it will most likely be a narrow band sensor.  They are accurate enough for the car's computer but not that accurate.  A better option would be a wideband sensor.  These sensors can read a bigger range of air/fuel ratios.  Your car should still start if the O2 sensor's heater wires are messed up as the sensor will heat up with the car exhaust.

No the car's computer does not know the difference between a real O2 or a resistor in most cases.  Some cars this does not apply to.

If you want a more accurate Air/Fuel readout you should go with a wideband O2.  These sensors have 5 wires most times.  I am currently trying to figure out how to make my own wideband O2 readout similar to what you did.  The only problem right now is cost.  The schematic i found uses a sensor that is about $200.  I have found units that you can buy that use a less expensive sensor but the unit retails for about $200.  So not much trade off.  I will try and post some schematic of the wideband O2 tonight.  If you want you can try and find them on the net.  search for DIY WBO2.  there will be a website WWW DIY-WB COM.  this is the site i got the schematic from, unfortunetly it is no longer up.  so you have to go to the internet archive page, www.archive.org and enter the website above and you can view the stuff on it.  THere is also an australian site that sells wideband o2 kits.  there website is wbo2.com.  They have some schematics on there, but i can't really understand them (too much of a newb right now)  maybe some of you guys can make sense of them and explain them to me.

I might have gotton to car technical if i did let me know i can explain further.  Hopefully with more time and help from everyone here, we can get a schematic for a wideband O2 that uses the less expensive sensor.

 

[thaivg]

Hi all,
May I use this circuit for Fuel indicator with LM3914? The resistance of rheostat on fuel tank as follows: 10 ohm when filled and 100 ohm when empty. Pls help me to design the input fo this circuit.
Thank you very much.

 

[audioguru2]

Hi all,
May I use this circuit for Fuel indicator with LM3914? The resistance of rheostat on fuel tank as follows: 10 ohm when filled and 100 ohm when empty. Pls help me to design the input fo this circuit.

Use a voltage regulator and add a fixed resistor to the rheostat so that the voltage to the input of the LM3914 changes as the rheostat resistance changes.

Do you know what is the maximum allowed voltage to the rheostat? You do not want it to make a spark that ignites the fuel.

 

[pegas77]

hello

is it possible to get the working final schematics?