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Need a simple adjustable device to lower signal voltage?

hevans1944

Hop - AC8NS
Jun 21, 2012
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@Alec_t: I bought an unheated Bosch O2 sensor years ago, thinking I could heat it to operating temperature with a Mapp gas blow-torch and learn a little more about how they work. Back in the day, my then employer, UDRI, was working on O2/CO2 sensors for a sponsored research project involving aircrew members. UDRI was purchasing very expensive sensors, which we technicians then instrumented and connected to an off-the-shelf airborne data acquisition system. IIRC, I never did fire up the Bosch sensor and run it through its paces, although I still have it out in my garage somewhere.

I am now using oxygen from an atmospheric oxygen concentrator, free courtesy of Medicare, because the ejection fraction of my failing heart is so low. Maybe now is the time to resurrect that O2 sensor and see how it works! Not too keen on mixing gasoline fumes with air (or oxygen) to put it through a workout however. I will let you know later if I decide to experiment and manage not to set the garage on fire or cause an explosion. Hmm. Maybe I could just mix some CO2 from dry ice to control the "richness" of the O2 sensor mixture.
 

supak111

★ƃuᴉɯǝɥɔs sʎɐʍlɐ★
Apr 29, 2012
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I'm not really sure if it must be a low impedance. I would have to do more testing, I suspect high impedance maybe ok for some vehicles and not other, low impedance would probably work on most cars/bikes
 

Cannonball

May 6, 2017
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Why not use a potentiometer? Top side to the signal source, bottom to ground, slider to adjust to the amount of signal you need.
 

supak111

★ƃuᴉɯǝɥɔs sʎɐʍlɐ★
Apr 29, 2012
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Why not use a potentiometer? Top side to the signal source, bottom to ground, slider to adjust to the amount of signal you need.

I can give a potentiometer a try. Was worried about burning out the oxygensensor and worse yet the engine computer. I'll put a 1k resistor inline with the ground just to be safe. And I also wonder what the voltage drop will be with say potentiometer set at 4k with the signal being at the 900mV and what the drop would be when the signal is 300mV. Wonder if its going to be same drop for the upper voltage and lower voltage.
 

supak111

★ƃuᴉɯǝɥɔs sʎɐʍlɐ★
Apr 29, 2012
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So basically what it comes down to is I need an analog to analog voltage stop down which has adjustable voltage step down, but from my limited knowledge everything now days is digital switching step up/down.
 

TCSC47

Mar 7, 2016
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A cautionary story. When I was training to be an electronic engineer way back in the late 60's, I came across the design rules for a small 12V to EHT inverter. I immediately adapted it to try and use it as an electronic ignition device for my car. I produced the 50KV needed for the spark plugs with no problems, and produced lovely UV emitting arcs across the spark plug gaps, on the bench. However, the old adage, "a little knowledge is a dangerous thing" was never more valid. What I had failed to appreciate was my lack of full awareness of how spark ignition is actually achieved and that the spark is generated when the point contacts open. I had assumed this happened when the points closed and that is what I designed my inverter to do! Thankfully I never got as far as trying to install it in my car, so I never found out what sort of damage that it would wreak.

I hope you see my point here. Stick to your own expertise and trust others who have spent a lot of time designing something to be manufactured in the millions to have got it right. If your oxygen sensor was designed to give a certain output, then that is the output that is correct.
 

Cannonball

May 6, 2017
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Your signal is analog and all you said you wanted to do was to reduce it. A pot will do the trick.
 

supak111

★ƃuᴉɯǝɥɔs sʎɐʍlɐ★
Apr 29, 2012
341
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A cautionary story. When I was training to be an electronic engineer way back in the late 60's, I came across the design rules for a small 12V to EHT inverter. I immediately adapted it to try and use it as an electronic ignition device for my car. I produced the 50KV needed for the spark plugs with no problems, and produced lovely UV emitting arcs across the spark plug gaps, on the bench. However, the old adage, "a little knowledge is a dangerous thing" was never more valid. What I had failed to appreciate was my lack of full awareness of how spark ignition is actually achieved and that the spark is generated when the point contacts open. I had assumed this happened when the points closed and that is what I designed my inverter to do! Thankfully I never got as far as trying to install it in my car, so I never found out what sort of damage that it would wreak.

I hope you see my point here. Stick to your own expertise and trust others who have spent a lot of time designing something to be manufactured in the millions to have got it right. If your oxygen sensor was designed to give a certain output, then that is the output that is correct.

Thanks for sharing you experience. Oxygen sensor is working as it should but I believe you are missing the point why I need it reduced. Me reducing the voltage the oxygen sensor produces will make the motorcycle fuel computer think its running lean (lack of fuel) and the engine computer will actually add more fuel to the engine which is safe for the engine.

95% of the time any performance modification you do to an engine, such as a simple high flow exhaust and a simple high flow air intake will cause the origin fuel map to be lean and lean on engines = more HP but also a BIG BOOOOM. Better to run rich and get less MPGS and less HP than a big BOOOOM. On the motorcycle I'm working on the engine computer is some what still dumb, closed and open loop are blurred, unlike on cars but we won't get into all that.

Your signal is analog and all you said you wanted to do was to reduce it. A pot will do the trick.

Will definitely try a simple potentiometer, will any pot do or does the watt rating on it matter? Again signal here is under 1v probably 20ma max but I haven't tested the current yet to be 100% sure.

PS do I put the pot inline with the signal wire or do I tap into the signal wire and run the pot to a ground?
 

Cannonball

May 6, 2017
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Tap into the signal wire to ground through the pot. The pot needs to be high enough value that it doesn't load the signal source. Take the wire where you cut to install the pot and connect it to the slider. Test it to make sure that it wont disturb the sensors 1/2 watt will do for the size.
 

supak111

★ƃuᴉɯǝɥɔs sʎɐʍlɐ★
Apr 29, 2012
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Hey everyone thanks for all the help. So I'm been messing around with this project and I wasn't just wondering if there is any way to accomplish this 0-300ma drop with a PWM?

I was thinking about using an Arduinos pwm to control. Though it would be cool to be able to program it at different rpms

Would
 
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