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LM3915 as LED fuel gauge?

I want toadd a set of gauges to my fuel management system. It will require one for each tank and 3 standard gauges take up to much room and cost a bunch so I am going to DIY it. Follow me through on this:

The sender is a variable resistor with a range of 240 Ohms empty to 33 Ohms full. If I put a 240 ohm resistor in series with the sender, feed it 3.3V and measure the voltage across the 240 Ohm resistor I will get a voltage from 1.65V empty to 2.9V full. That is a range of 1.25V in a more or less logarithmic curve. If I feed this voltage to an LM3915 LED driver I can display the tank levels on a 10 segment LED array.

There is only one problem. How do I set the zero to 1.65V?

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at:  http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com
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Glenn Ashmore
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Thanks. That should work and not be effected by minor supply voltage variations.

-- Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at:

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Shameless Commercial Division:
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require

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an

Reply to
Glenn Ashmore

"Glenn Ashmore" schreef in bericht news:mO9Md.113838$Wo.54030@lakeread08...

Use an opamp to subtract the 1.65V. An old CA3140 will do.

VCC + | +-+-------+----------------+ | | | .-. .-. | ___1k | |33- | |10k +-----|___|-+ | |240 | | | | | '-' '-' | | | | | 1k ___ | |\| | | +-----|___|--+-|-\ | out | | | >------+---- +----------------------|+/ CA3140 | | |/| | | | .-. .-. | | |240 | |10k | | | | | | '-' '-' | | | | ++-------+----------------+ | === GND created by Andy´s ASCII-Circuit v1.24.140803 Beta

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If your environment is noisy you can reduce the 10k resistors and/or put an elco 1-10uF parallel to the lower 10k. You can make a zero adjust with a

100-220 Ohm trimpot between the two 10k resistors, its tab to the 1k input resistor of the opamp.

petrus bitbyter

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petrus bitbyter

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