Extra credit (for electrically inclined)

[Dave]

Looking to get some extra credit in class. Our instructor gave us a challenge question for some extra points tomorrow. The question is: In an A/F gauge... If a Zirconia oxygen sensor produces a voltage that ranges from .1 to .9 V, when sent through 9 Zener diodes, all graduating from a point of inverse range of .1 to .9 volts it will bias each diode once the PVI is reached. Now of course that works, but why will this not work in an A/F gauge?

My only guess is that if wired in parallel it will bias each diode which then will bias their own individual LED, but if ran in parallel it will bias all 9 if the O2 sensor is sending out .9 volts. So you would essentially need 9 seperate outputs from the O2 to light each LED individually. The intention is to light only one LED, not all 9.

I guess that could be the only problem, but how would I fix that? Is the only real answer 9 outputs. Is that even practical?

[Clay]

hmmmm sounds like you have more work to do if you want to get that extra credit! ;)

[karlak]

series parallel ckt pops in my head....... will have to do some ciphering tonight
not..... not...... double not...... me and Jethro

[lametec]

Does an O2 sensor combined with Zener diodes really work? If would think the O2 sensor would be incapable of producing enough current for the Zener to break down.. And where do you find Zeners with a break down voltage of 0.1 to 0.9 volts?

Even if the O2 sensor supplied enough current to drive the zeners, you'd still need drivers for the LEDs.

[Mopar_Nutz]

Cheater. no fair asking for answers! :p

[looneytuner]

Looking to get some extra credit in class. Our instructor gave us a challenge question for some extra points tomorrow. The question is: In an A/F gauge... If a Zirconia oxygen sensor produces a voltage that ranges from .1 to .9 V, when sent through 9 Zener diodes, all graduating from a point of inverse range of .1 to .9 volts it will bias each diode once the PVI is reached. Now of course that works, but why will this not work in an A/F gauge?

My only guess is that if wired in parallel it will bias each diode which then will bias their own individual LED, but if ran in parallel it will bias all 9 if the O2 sensor is sending out .9 volts. So you would essentially need 9 seperate outputs from the O2 to light each LED individually. The intention is to light only one LED, not all 9.

I guess that could be the only problem, but how would I fix that? Is the only real answer 9 outputs. Is that even practical?

HUH????????

[Dave]

HUH????????

You seem confused. :p

Basically my instructor said an O2 sensor, being a battery in itself, will produce enough voltage to bias a Zener diode. We're looking at doing this in an A/F gauge. Bias the zener, then bias a LED. Basically we have 9 Zener's to bias, and 9 LEDs to bias. 18 total diodes. Yes, if you get a diode with a PIV low enough, it will bias.

Why will this not work in an A/F gauge and how do I fix it? I've came to the conclusion that the difference in potential between each series of diodes will turn off the previously lit diode once the present diode is biased.

Bam! Nevermind, thanks though guys.

[BadAssPerformance]

Now a better question...

Why in the hell would you wire any diodes to the O2!?

[GLHNSLHT2]

but how would I fix that?
The only fix is to throw the O2 and a/f gauge in the garbage and install a Wideband setup :dancingbana:

[Frank]

You are talking about a resistor/diode ladder... your 9 LEDs tell you your A/F....

[Dusty_Duster]

Looking to get some extra credit in class. Our instructor gave us a challenge question for some extra points tomorrow. The question is: In an A/F gauge... If a Zirconia oxygen sensor produces a voltage that ranges from .1 to .9 V, when sent through 9 Zener diodes, all graduating from a point of inverse range of .1 to .9 volts it will bias each diode once the PVI is reached. Now of course that works, but why will this not work in an A/F gauge?

My only guess is that if wired in parallel it will bias each diode which then will bias their own individual LED, but if ran in parallel it will bias all 9 if the O2 sensor is sending out .9 volts. So you would essentially need 9 seperate outputs from the O2 to light each LED individually. The intention is to light only one LED, not all 9.

I guess that could be the only problem, but how would I fix that? Is the only real answer 9 outputs. Is that even practical?

I'm an electrical engineer, and I've got no clue what you're trying to do from reading your statement there. Got a diagram?

[Dave]

Well the actual answer was... the problem was that the O2 sensor does not produce enough voltage to bias a LED (1.5V-2.5V) and a zener diode. You need to amplify the voltage before the ladder. The way to do that is to install either, 1. a compound transistor, NPN to a PNP or 2. Build an amplifier: O2 to the base of a PNP transistor then the battery voltage is connected to the emitter, then the collector travels to the rest of the circuit. This will multiply the O2 sensor input by a given percentage.

My thoughts were correct as well. So I got partial credit. In order to turn one LED off when another comes on is to construct a logic gate. I did this last night before even learning about logic gates. This is a bit too complex to explain online, but I can draw a picture in paint if anyone is interested.

Does this make more sense?

[MiniMopar]

Yeah, I was gonna say.... Plus, I have never heard of a 0.1V zener. The lowest forward-bias I can think of is a Schottky diode...around 0.4-0.5V.

Nevermind that a single LM3419 to do everything is cheaper than all of those diodes and an amplifier.

[Dusty_Duster]

I was going to suggest amplifying the O2 sensor. This would do several things for you:
1. The O2 sensor, which cannot source much current, would be driving a high-impedance load.
2. You could amplify the voltage from 0-1V to 0-10V, giving you more of a dynamic range to use with the zeners.

At the output of the amp, you could wire into the zeners, and then wire the output of the zeners into a logic circuit.

Are you taking a technical electronics course, or are you majoring in electrical engineering?

[Dave]

I was going to suggest amplifying the O2 sensor. This would do several things for you:
1. The O2 sensor, which cannot source much current, would be driving a high-impedance load.
2. You could amplify the voltage from 0-1V to 0-10V, giving you more of a dynamic range to use with the zeners.

At the output of the amp, you could wire into the zeners, and then wire the output of the zeners into a logic circuit.

Are you taking a technical electronics course, or are you majoring in electrical engineering?

It's a class part of automotive technology. The longest class out of the entire course, actually. :) I've taken a strong attraction to electronics and I'm deciding if that's what I want to do now. Damn college!