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Looking for some design help (automotive)...

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Toolmaster

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Hi all! Thanks in advance if you're able to help me here...

It's been 20+ years since I've toyed around with circuits, and I'll admit I forgot most of what I used to know.

My application is as follows:

I have a gauge in my car, that reads pressure (turbocharged car application). I'd like to drive that gauge with a different sender. Stock form, the sender drives the gauge from 0v to 5v, on a scale of 0psi to 28ish psi (14.7psi is atmospheric pressure - or at least thereabouts) , and the signal is linear. I'd like to replace the sender with a different one, which will also provide 0v-5v output, but on a different scale.

To clarify - right now, when my car is boosting to 1 bar (14.7psi), I get 2.5v out of the existing sender. IF I place the new sender in there, I'll get a smaller voltage, because the new sender has a larger range of values. Figure the new sender will have a range of 0-44 psi, so if I do the math, I expect to see about 1.666v. I want to be able to basically change the scale of the output so that the output of 1.666v from the new sender will actually send 2.5v to the gauge. Basically, it's a calibration circuit, and the new sender is also linear.

Ideally, I'd like to have a good way of selecting my range of voltages for the new sender, so I can use almost any sender I can find. Also, I'd love to be able to dial in the new sender and gauge, so that i can set the gauge to read any desired boost pressure. Like if I wanted the marking of 1 bar on the gauge to be atmospheric pressure, adjust a pot thusly, or if I wanted the 1 bar on the gauge to be 1 bar of boost, adjust accordingly.

So the circuit I'm looking for will read the input voltage, convert it to a different voltage, which could be higher or lower, (in a linear fasion) and then output that to my gauge. The circuit shouldn't send more than 5v to the gauge, ever.

Hoping someone can give me a hand... If this isn't the right place for this post - sorry...

Thanks!

Jay
 

Willbe

New Member
I'd like to drive that gauge with a different sender.
the sender drives the gauge from 0v to 5v
the signal is linear.
which will also provide 0v-5v output, but on a different scale.

I get 2.5v out of the existing sender.
I expect to see about 1.666v.
I want to be able to basically change the scale of the output so that the output of 1.666v from the new sender will actually send 2.5v to the gauge.
So you need a gain of 2.5/1.7 = 1.47.

I'd like to have a good way of selecting my range of voltages for the new sender, so I can use almost any sender I can find.
The gain must be variable over some range.

which could be higher or lower
So an attenuator and then a variable gain, over some range.

send more than 5v to the gauge, ever.
A Zener equivalent somewhere in the circuit that clamps the output.
You'll also need a rugged meter movement, maybe with heavy damping.

What are specs for the candidate sending units and your indicating meter?
 

Toolmaster

New Member
Thanks!

The sensor I'm going to use will have an output of 0-5v, no matter which one I decide to use... So that's a constant.

The gauge I'm not totally sure about, other than how it's driven through the stock computer, which is though a series of small resistors.

Does that help any? Thanks for the reply!
 

Willbe

New Member
The sensor I'm going to use will have an output of 0-5v, no matter which one I decide to use... So that's a constant.

The gauge I'm not totally sure about, other than how it's driven through the stock computer, which is though a series of small resistors.

Does that help any? Thanks for the reply!
So the sensor is not two-terminal resistive but three terminal with a voltage output.
How much current can it source, or how low a resistive load does the manu. recommend it be driving?
If it outputs enough power we may only need a variable attenuator to drive the meter.
 
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