Air/Fuel Ratio guage Circuit - Electronic Circuits Projects Diagrams Free

Gotrek · 5th December 2003, 01:39 PM

As the subject says I'm looking into building a circuit to display the air fuel ratio of a car, I was thinking of using 10-20 LEDs to indicate from lean to rich using various colored LED's. I found various plans online that use the LM3914 driver. I was wondering if anyone had any experience building this type of circuit (which in essence is just a voltmeter really) it will read voltage from the O2 sensor.

I was wondering if there was a way to only have on LED light up at a time instead of having them light up progressively. I'm not sure how to do this all the plans I've found light them all up as the voltage goes up.

fat-tony · 5th December 2003, 02:31 PM

I've got answers

First thing I'd like to point out is that you're probably looking for the LM3914, not the 9314...

http://www.national.com/ds/LM/LM3914.pdf

But the second answer is better. If you check out page 7 of that, they describe how to put it into bar or dot mode, including a mode using dot display with over 20 LEDs.

All of these are set using pin 9 (the "mode" pin). For normal dot, you just leave the "mode" pin open. For normal bargraph, you short the "mode" pin directly to pin 3 (V+). The huge graph is more complex, and you can read all about it if you want.

Gotrek · 5th December 2003, 02:33 PM

You're correct about the chip I edited my other post thanks, and Thanks for the document thats exactly what I want

eemage21 · 6th December 2003, 02:24 AM

I put a gauge pcb together for a friend. You will achieve the best results using curved segmented LEDs.

Gotrek · 8th December 2003, 11:52 AM

Yes that probably what we were going to do, possibly also using a larger LED to indicate Stoich, lean, and rich

Gotrek · 9th December 2003, 11:51 AM

I found a simple diagram I'm going to follow But since I'm not an electronics guru could someone tell me what kind of part T1 and T2 represent? They are valued at 5k ohm but are they resistors? Thermistors? I don't know anyone have a clue? (I'm sure you all do)

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fat-tony · 9th December 2003, 03:22 PM

I'd suspect that T1 and T2 are just variable resistors. They set up the biasing for your reference voltage.

Gotrek · 9th December 2003, 03:27 PM

After looking up pictures of varible resisotrs I believe you are correct, thanks a bunch.

Like the silver boxes and the thing with the yellow screw type thing on tope right? Not the circled objects (nice tech talk ehh?)

Gotrek · 9th December 2003, 04:05 PM

I'm on Digikey ordering the stuff, can someon tell me What power dissipation value I want?

I need top adjusting, 5k ohm variable resistors but I'm not sure what wattage rating I need

Roff · 9th December 2003, 08:49 PM

That circuit will only monitor voltages of 1.25v or less. If you were to use that circuit as drawn, you should connect a 620 ohm resistor in series with T2, which is the LED brightness control. This will limit LED current to about 20ma each, which still may be too much current for the LM3914 if all LEDs are on and your LED supply voltage is more than about 8 or 9 volts.

What is the range of the voltage you are wanting to monitor? What is your supply voltage? How much current do you want to run through each LED? Answer these questions and we (I) can draw a complete schematic for you. I know that you said you wanted dot mode as opposed to bar mode. This will save power.

Gotrek · 10th December 2003, 11:43 AM

I hope this helps

Basicly measuring from 0 ro 1 volt, input is 12volts

I plan on not connecting Pin 9 so only one LED should light at once

I stole the picture/circuit from http://www.ffp-motorsport.com/tuning/o2meter.php

Eclipsed · 10th December 2003, 12:25 PM

Just so you know, that pic isn't even close to being correct.Outside of stoich there is no way of reading actual(or even ballpark) A/F from a normal oxygen sensor.They are effected too heavily from exhaust temperature.Over time they can help you get a "feel" of how your engine is operating, but don't think they are even close to correct A/F.I've seen more than one engine damaged from people thinking o2 voltage is some indication of A/F.

Gotrek · 10th December 2003, 12:32 PM

Ahh ok, the A, B, C on the graph represent the different curves based on different temperatures for the Lamda sensor, I guess that explains it

Gotrek · 7th January 2004, 04:25 PM

Sorry to bump up this old post but in the picture of T1 and T2 what are the pin assignements? I'm not sure how to wire it up.

njcfm · 8th January 2004, 08:37 PM

a a/f gauge off of a stock 02 sensor is pretty much worthless..

it won't really give you any USEFUL information other than the 02 sensor is actually working.

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5th December 2003, 01:39 PM	(permalink)
Gotrek	Air/Fuel Ratio guage Circuit As the subject says I'm looking into building a circuit to display the air fuel ratio of a car, I was thinking of using 10-20 LEDs to indicate from lean to rich using various colored LED's. I found various plans online that use the LM3914 driver. I was wondering if anyone had any experience building this type of circuit (which in essence is just a voltmeter really) it will read voltage from the O2 sensor. I was wondering if there was a way to only have on LED light up at a time instead of having them light up progressively. I'm not sure how to do this all the plans I've found light them all up as the voltage goes up.

5th December 2003, 02:31 PM	(permalink)
fat-tony	I've got answers First thing I'd like to point out is that you're probably looking for the LM3914, not the 9314... http://www.national.com/ds/LM/LM3914.pdf But the second answer is better. If you check out page 7 of that, they describe how to put it into bar or dot mode, including a mode using dot display with over 20 LEDs. All of these are set using pin 9 (the "mode" pin). For normal dot, you just leave the "mode" pin open. For normal bargraph, you short the "mode" pin directly to pin 3 (V+). The huge graph is more complex, and you can read all about it if you want.

5th December 2003, 02:33 PM	(permalink)
Gotrek	You're correct about the chip I edited my other post thanks, and Thanks for the document thats exactly what I want

6th December 2003, 02:24 AM	(permalink)
eemage21	gauges I put a gauge pcb together for a friend. You will achieve the best results using curved segmented LEDs. __________________ \"There are only 10 types of people in the world: those who understand binary, and those who don\'t...\"

8th December 2003, 11:52 AM	(permalink)
Gotrek	Yes that probably what we were going to do, possibly also using a larger LED to indicate Stoich, lean, and rich

9th December 2003, 11:51 AM	(permalink)
Gotrek	I found a simple diagram I'm going to follow But since I'm not an electronics guru could someone tell me what kind of part T1 and T2 represent? They are valued at 5k ohm but are they resistors? Thermistors? I don't know anyone have a clue? (I'm sure you all do) [/img]

9th December 2003, 03:22 PM	(permalink)
fat-tony	I'd suspect that T1 and T2 are just variable resistors. They set up the biasing for your reference voltage.

9th December 2003, 03:27 PM	(permalink)
Gotrek	After looking up pictures of varible resisotrs I believe you are correct, thanks a bunch. Like the silver boxes and the thing with the yellow screw type thing on tope right? Not the circled objects (nice tech talk ehh?)

9th December 2003, 04:05 PM	(permalink)
Gotrek	I'm on Digikey ordering the stuff, can someon tell me What power dissipation value I want? I need top adjusting, 5k ohm variable resistors but I'm not sure what wattage rating I need

9th December 2003, 08:49 PM	(permalink)
Roff	That circuit will only monitor voltages of 1.25v or less. If you were to use that circuit as drawn, you should connect a 620 ohm resistor in series with T2, which is the LED brightness control. This will limit LED current to about 20ma each, which still may be too much current for the LM3914 if all LEDs are on and your LED supply voltage is more than about 8 or 9 volts. What is the range of the voltage you are wanting to monitor? What is your supply voltage? How much current do you want to run through each LED? Answer these questions and we (I) can draw a complete schematic for you. I know that you said you wanted dot mode as opposed to bar mode. This will save power.

10th December 2003, 12:25 PM	(permalink)
Eclipsed	Just so you know, that pic isn't even close to being correct.Outside of stoich there is no way of reading actual(or even ballpark) A/F from a normal oxygen sensor.They are effected too heavily from exhaust temperature.Over time they can help you get a "feel" of how your engine is operating, but don't think they are even close to correct A/F.I've seen more than one engine damaged from people thinking o2 voltage is some indication of A/F.

10th December 2003, 12:32 PM	(permalink)
Gotrek	Ahh ok, the A, B, C on the graph represent the different curves based on different temperatures for the Lamda sensor, I guess that explains it

7th January 2004, 04:25 PM	(permalink)
Gotrek	Sorry to bump up this old post but in the picture of T1 and T2 what are the pin assignements? I'm not sure how to wire it up.

8th January 2004, 08:37 PM	(permalink)
njcfm	a a/f gauge off of a stock 02 sensor is pretty much worthless.. it won't really give you any USEFUL information other than the 02 sensor is actually working.